Final Report for SW09-062
This project demonstrated that regional farms harbor a diverse assemblage of ground beetles that vary in their habitat use, per capita feeding voracity and seasonal activity patterns. In aggregate, beetles increased the risk of predation faced by potential pests within crop fields. However, the risk faced by pests was reduced on farms that lacked perennial grass and other less disturbed habitats, particularly early in the season. Maintaining less disturbed areas on a farm, as well as augmenting habitat in the form of beetle banks, can ensure a diverse mix of ground beetles and a high level of pest suppression capacity.
The overarching goal of this project was to provide farmers with information that would help them better manage ground beetle assemblages on their farms and to maximize the biocontrol benefits they provide. Our specific research and outreach objectives were:
1. Develop a habitat-based model that predicts the occurrence of beetle species at the farm-scale in Pacific Northwest agricultural landscapes.
2. Determine how the farm-scale arrangement of habitat types influences beetle activity patterns within fields.
3. Determine how beetle activity within fields influences prey consumption.
4. Provide specific recommendations based on farmer-generated research questions.
5. Facilitate regional cooperation among farmers and researchers developing conservation biological control.
This project provided guidelines for implementing generalist predator habitat (beetle banks) on farms in the Pacific Northwest. Improving habitat for generalist predators, such as ground beetles, is a promising biological control strategy that offers an alternative to pesticide use. In a previous Western SARE-funded project (FW06-324), we introduced the concept of beetle banking to regional farmers, and several of them installed some of the first beetle banks in the region. These farmers identified a number of significant knowledge gaps that, in their view, hindered the more widespread implementation of beetle banks in the region. Farmers wanted criteria for assessing the beetle habitat status of their farms, better guidance on the optimal construction of banks, and evidence that banks actually improve pest suppression. This project was designed to provide some answers to these questions.
Historically, the practice of manipulating and managing natural enemies for the biological control of pests has focused on the planned introduction of specialist predators and parasitoids (Greathead 1985). However, a growing body of evidence has documented the biological control value of existing assemblages of generalist natural enemies (Symondson et al. 2002, Stiling and Cornelissen 2005). Conservation biological control attempts to maintain and enhance these assemblages within agricultural landscapes (Landis et al. 2000). Assemblages of generalist natural enemies have a number of potential advantages over specialists, including the potential for positive interactions among natural enemy species and the potential for enhanced suppression of pest outbreaks through mechanisms such as density dependent prey switching (Riechert 1992, Losey and Denno 1998, Cardinale et al. 2003, Snyder et al. 2006). However, natural enemies can also potentially negatively interact with each other through mechanisms such as intraguild predation, and other life history characteristics can limit the ability of generalists to suppress pest outbreaks (Rosenheim et al. 1995, Snyder and Ives 2001, Koss and Snyder 2004). These complications can make it difficult to predict the actual biocontrol efficacy of generalist assemblages (Symondson et al. 2002, Snyder and Ives 2003).
Ground beetle assemblages illustrate this complexity. Ground beetles are generalist predators that feed on invertebrates and plant seeds. A number of studies have demonstrated that both individual ground beetle species and species assemblages contribute to lower pest abundance in agricultural systems (Brewer and Elliot 2003, Edwards et al. 1979, Kromp 1999, Sunderland and Vickerman 1980). Ground beetles can play an important role in limiting pest outbreaks on farms by concentrating their feeding activity in areas of high pest abundance (Winder et al. 2005, Bell et al. 2010). Ground beetles can also synergistically interact with other natural enemy guilds to reduce pest populations (Losey and Denno 1998, Snyder and Ives 2003).
However, a number of factors complicate our ability to predict the extent to which ground beetles limit pest numbers in actual farm landscapes. First, species differ widely in their specific feeding habits, and it may be only a few species that are responsible for the biological control of specific pests (Sunderland and Vickerman 1980, Prasad and Snyder 2004). Second, ground beetle feeding behavior can be affected by factors other than prey abundance, such as relative hunger, size, breeding status and seasonal preferences (Wallin et al.2004, Lovei and Sunderland 1996, Honek et al. 2006). Third, ground beetle species differ in their overall habitat preferences, and habitat use can vary considerably over the course of a season (Holland et al. 2005, Holland et al. 2009). Because of these factors, it is likely that ground beetle activity patterns, as well as the biocontrol potential associated with that activity, is strongly influenced by the specific life history traits of the species composing local beetle assemblages. Although the literature on ground beetles is large and diverse, pertinent life history information for many species is still scarce. In addition, there are few studies that comprehensively document how the dynamics of whole beetle assemblages influences pest suppression potential within farm landscapes. This lack of information makes it difficult to assess how regional and local variation in the composition of beetle assemblages influences the nature of the biological control they provide.
In the U.S. Pacific Northwest, ground beetles are known to play a potential role in pest suppression, but we lack a full understanding of how variation in life history and habitat use characteristics among individual species contributes to overall pest suppression potential on farms. Several ground beetle species in the northwest are known to include pest invertebrates and weed seeds in their diet based on laboratory feeding trials and gut analyses of field caught specimens (Prasad and Snyder 2004, Moulton 2011). Several species are also known to forage widely within agricultural fields during the summer but depend on less disturbed grassy areas during the winter (Prasad and Snyder 2006). Pesticide use and tillage practices can affect ground beetle abundance, but the specific effects vary considerably among species (Green 2011, McGrath 2000).
Unfortunately, we currently do not have information on the long-term habitat use dynamics of ground beetle assemblages in the region. In addition, there are many other species that are common in Pacific Northwest agricultural areas for which little is known about basic life history characteristics and habitat affinities.
Prasad and Snyder (2006) demonstrated that interactions between specific life history characteristics in the form of intraguild predation and the preference for alternative prey can indeed influence the level of biological control provided by ground beetles in the Pacific Northwest. It is likely that other life history traits, as well as the spatial and temporal patterns of habitat use by individual species, influence the overall biocontrol provided by beetles in specific landscapes. The risk that a pest is eaten by a ground beetle is a function of both the likelihood that a pest and a beetle encounter each other and the likelihood that the beetle includes the pest in its diet. Estimating the comprehensive risks that pests face from rich ground beetle assemblages requires developing a fuller understanding of how beetle species differ in their habitat use relative to crop fields and pest phenology (encounter risk) and how beetles differ in their life history traits relative to pest feeding behavior (consumption risk).
Research materials and methods
This project was conducted on five Pacific Northwest vegetable farms; four in the Willamette Valley of Oregon and one in the Columbia Palateu of eastern WA. The Willamette valley farms were located within a relatively diverse landscape, consisting of other cultivated crops like fruit, berries and seed production; urbanized areas; and more natural vegetation such as riparian corridors. The WA farm was located within a less diverse agricultural landscape, consisting of large center pivot irrigated fields. All the farms grew a wide variety of vegetable crops; the WA farm also grew some cereal grains. All farms had intentionally created grassy habitat to provide shelter for over-wintering ground beetles (beetle banks) in some of their fields. One of the Willamette Valley farms was not USDA certified for organic production but practiced cultivation guidelines that were largely consistent with organic guidelines, with the exception of the occasional use of herbicides. The other four farms were certified organic.
On-farm habitat description
We produced detailed GIS based vegetation maps for each of our cooperator farms using high resolution aerial photographs and ground sampling. The aerial photographs consisted of 0.5m orthoquads encompassing a 1.5 km radius circular area centered on each farm. We then hand-digitized habitat patches visible on the orthoquads and assigned the patches to specific habitat categories using ground surveys of each site. We classified vegetation into broad vegetation types commonly found in PNW agricultural landscapes (riparian forest, coniferous forest, mixed deciduous forest, perennial grassland, annual cropland, herbaceous field margins, conservation habitat such as beetle banks, hedgerows, insectary plantings).
Characterization of beetle activity and habitat use
We sampled beetle activity relative to the major habitat patches on each farm using pitfall traps during the active spring and summer seasons and soil cores during the winter. Pitfall sampling occurred monthly during two growing seasons (2010-2011) and soil core sampling occurred monthly for three growing season (2009-2011). At each farm pairs of traps were arrayed along transects extending across fields and stratified by the major habitat types on each farm.
Non-lethal pitfall traps were used to minimize the effects of repeated sampling on the farms and to provide live beetles for laboratory trials. Pitfall traps consisted of a plastic pint (473 ml) cups with a 100 mm diameter at the top. A funnel was fitted in the rim of the main cup to prevent insects from escaping by climbing back up the side of the cup. A smaller cup in the bottom of the main cup had a hole in it to allow the smaller species to escape to an area within the trap that is safe from predation by any of the larger species. The rim of the main cup was buried flush with the soil surface and an aluminum lid was placed over the set up to keep out rain and irrigation water.
Pitfall traps were set out as close to the same location each month as possible. The habitat type, dominant plant functional group and recent management activities were assessed at each trap location during each sampling event. Traps were opened for two nights before they were checked and the occupants identified and tallied. Most of the collections were released immediately, but some beetles were collected for lab experiments (see below), and vouchers were collected for each ground beetle species identified. The occurrence of teneral beetles (beetles that have recently emerged from their pupae ) was noted on the sampling days that they were caught. The ground beetles were identified to species based on Lindroth (1969).
Occasionally, field cultivation or flooding would prevent the opening of a trap, or would destroy it, making data collection impossible. Therefore during some of the months not all of the trap sites were sampled. These missing data represented only 5.1% of total trap sampling records.
During the winter, beetles were sampled using soil cores in each of the major habitat types on the farm. Plots were randomly located in representative patches in each of the main habitat types on the farm. Paired cores were taken at each plot to make a better estimate of the invertebrate community. The habitat type and the dominant plant species and growth form were recorded at each sample location. Soil cores were taken with a 15 by 20 cm steel frame that was pounded 15 cm into the ground. Each pair of soil cores was transported to a lab where the cores were broken up by hand while being placed as pairs into Berlese funnels. An incandescent light was used to dry the soil and drive the inhabitants out of the cores and into collecting jars filled with ethanol. The soil was checked for dryness frequently, and it generally took between two to four weeks for the soil to become completely dry. When the soil was dry, the invertebrates, soil and other debris that had fallen in the sampling jar were strained from the alcohol. The invertebrates were sorted from the other material and tallied. This study focuses on the ground beetles, which were identified to species based on Lindroth (1969).
Assessment of predation risk for pests
The risk of predation faced by potential prey items on each of the study fields was assessed using sentinel prey cards placed adjacent to each pitfall trap. Drosophila melonagaster pupae were chosen as the sentinel prey item because of their availability and reports that they are an acceptable food choice for a variety of carabids (Carcamo and Spence 1994). Twenty freeze-killed pupae were attached to cards with a flour and water paste. The cards were suspended slightly off the ground by a hat pin. A cylinder of 1 cm wire mesh created the walls of an exclosure with a small plastic food tub creating a roof to shed rain and irrigation water. The exclosures allowed entry of ground beetles and smaller organisms but prevented small mammals from accessing the sentinel prey cards. The number of pupae eaten was tallied after the two sample nights.
Slugs were attracted to the flour paste and could damage the cards. We noted whenever prey cards were clearly destroyed by slugs and those samples were excluded from analysis. Excluding these prey damaged cards reduced to total number of usable prey card assays by 44%. For analysis we pooled the monthly prey card assays into three four-month seasons per year. There were 1,748 potential seasonally pooled estimates for each site during each four month interval over the two years of the study.
Assessment of seasonal variation in per capita feeding rate and prey preferences
We used microcosm feeding trials of field caught beetles to assess how per capita feeding and prey preferences varied seasonally and across beetle species. During each sampling period on the Willamette Valley farms, we collected 15 individuals of each of the common large and midsized species for use in microcosm feeding trials conducted at Oregon State University. Beetles were placed in feeding arenas created by filling large plastic tubs (approximately 50 by 35 cm by 25 cm deep) with about 2 cm of moistened sand. The tubs were covered with a lid and placed on the ground in a shady area. Five individuals of a single species were placed in each tub along with five sentinel prey cards (100 fly pupae total). After two days, the number of pupae eaten from each card was counted. The sum of the pupae eaten from all five cards was divided by the five beetles in the box to calculate a mean per capita number of pupae eaten over the two days in the arena.
After the first feeding trial, the beetles were removed from the arenas and brought inside the lab for a feeding choice trial. These trials were conducted in a smaller (15 cm by 30 cm base) box with only a moist paper towel for bedding so it would be possible to distinguish true seed predation from caching behavior that ground beetles sometimes exhibit (Manley 1971, Hartke, et al. 1998). Three beetles of one species were placed in each box. One sentinel prey card with 20 fly pupae on it and a moistened piece of filter paper with 20 imbibed Amaranthus retroflexus (pigweed) seeds were placed in the box with the beetles. Amaranthus seeds are known to be readily consumed by ground beetles in other studies (Lund and Turpin 1977). The boxes were left in the lab overnight, and the numbers of items eaten were checked after 24 hours.
Assessment of beetle reproductive condition
At the end of the feeding trials beetles were freeze-killed and stored frozen. Frozen beetles were dissected to determine their fertility state. Male ground beetles of many species can be identified by the presence of special pads on the protarsi, while females lack the pads. Up to five females of each species from each sample period were dissected. Each dissected beetle was measured in millimeters, it was checked for the presence of developed flight wings, and then it was dissected to check for the presence of eggs. The eggs, which are clearly visible as they accumulate in female oviducts, were tallied to document beetle fertility state (Luff 1973).
We developed statistical models that related the occurrence and activity of the beetle species we encountered during sampling to the abundance and arrangement of habitat types on each farm (Objectives 1-2). The overall mean activity density was calculated for each species at each pitfall trap site for each sample period. These means were used to estimate the beetle presence within different habitat types during the activity season of the beetle. Analysis of variance and Tukey’s Honestly Significant Difference multiple comparison tests were used to test for differences in the number of beetles from each species that were trapped within different habitat types.
The winter soil cores provided an estimate of actual overwintering density within each habitat type. We used analysis of variance and Tukey’s Honestly Significant Difference multiple comparison tests test for differences in the density of overwintering ground beetles in each habitat type.
We used linear regression to test the hypothesis that risk of predation was related to the activity density of each beetle group during each season (Objective 3). For the voracity feeding trials, analysis of variance and Tukey’s Honestly Significant Difference multiple comparison tests were used to test for differences between the mean number of pupae eaten by each species. In the prey choice feeding trial, the response variable was the ratio of the number of seeds consumed to the total number of items consumed including both seeds and the fly pupae. This is a preference measurement with values falling closer to zero representing a preference for insect prey, and values close to one representing a preference for seeds. Analysis of variance and Tukey’s Honestly Significant Difference multiple comparison tests were used to test for differences between the species in the mean seed to total consumption ratio.
The core components of our outreach program were grower-researcher meetings, on-farm demonstrations of research activities and field classes. We also disseminated information through Oregon State University Extension Publications and websites that summarized best practices for assessing and improving predacious ground beetle habitat on farms in the PNW.
Activity patterns and habitat use on farms
Each beetle species had its own pattern of activity and habitat use over the course of the year. The greatest mean monthly activity density for a single species was more than five beetles per trap during the August peak in activity of Pterostichus melanarius. None of the other species had a monthly mean activity density of more than one beetle per trap. Among the large species, only Omus audounii was active in the spring and early summer. The other large species were active later in the year, with P. melanarius and Harpalus pensylvanicus most active in the late summer and Pterostichus algidus and Scaphinotus marginatus in the fall (Figure 1). All the midsized beetles were active in the spring and early summer. The Amara and Agonum species had peak activity earlier in the season than Harpalus affinis and the Anisodactylus species. Nebria brevicaulis had both the earliest activity of any midsized beetles and a second activity season in the fall (Figure 1).
The most abundant small species, Trechus obtusus, was active in the fall. Small species also had maximum activity during the spring and summer. The Bradycellus species had peak activity in August, while Microlestes linearis and the Bembidion and Stenolophus species had peak activity in July (Figure 1). Acupalpus meridianus, with peak activity in June, and Clivina fossor, with peak activity in May, were the most common small species, with spring to early summer activity seasons. Loricera foveata is the only species that was very active during the winter, with a peak activity in February.
Overall, the beetle community was numerically dominated by the large species P. melanarius. In the spring and early summer, P. melanarius is not active in large numbers, so the midsized beetles as a group had the highest activity density (Figure 2). A variety of small beetles were active over the growing season but in relatively lower activity densities than the larger species. Only in January and February, when L. foveata was the only active specie, were there more small beetles than other species in the traps.
Beetle habitat use on the landscape varied over the seasons. During the growing season the highest activity density was in annual fields, while over the winter the largest populations of beetles were found in perennial margins (Figure 3).
For all of the common beetle species, there were significant differences in the pitfall trap catch of beetles in habitats dominated by different plant functional groups (Table 1). For most species, the greatest activity was seen in recently tilled crop fields dominated by annual plants, or with no established vegetation. Habitats dominated by perennial herbaceous plants had sharply lower activity, while numbers caught were lower still in habitats dominated by woody perennials (Figure 4). A few large species, including Pterostichus algidus, Omus audouini and Scaphinotus marginatus, had maximum activity in habitats dominated by perennial vegetation and only limited activity within crop fields (Figure 5).
Not all of the species collected in the summer were present as adults in the winter soil cores. For the species that were present, the majority were collected from areas dominated by dense perennial grasses and forbs. The number of over wintering adult carabids collected from cores was significantly (F2/167 = 3.9, P = 0.02) higher in areas dominated by perennial herbaceous vegetation and very low in annually tilled fields or areas dominated by woody vegetation (Figure 6). This is a striking difference from the summer distribution where these species were primarily active in the annual crop fields.
The habitat use patterns of the beetles on the farms in this project correspond with the results from a common garden experiment that tested how structural components of vegetation influence beetle activity and abundance. This common garden study was done in support of the main objectives of this project. A detailed description of the results from that study are supplied in (Appendix I)
Influence of beetle activity patterns on prey consumption risk
The per capita voracity of each beetle species, measured as the mean number of fly pupae eaten over each two day trial by the five beetles in the box, differed significantly between species (F16/356 = 31, P < 10-15). There was a general trend for larger species to eat more than smaller species, with the largest species eating nearly all (20 per beetle) of the pupae, and smaller beetles eating fewer than 10 pupae per beetle (Figure 7). Scaphinotus marginatus and O. audouini are two large beetles that ate very few pupae, suggesting that the items presented were not an acceptable food for those species.
The trend for larger beetles to eat more fly pupae is best seen in the midsized beetles. The large beetles often ate all of the available fly pupae so the results from the trial are likely to be underestimates of prey consumption capacity. Looking at the midsized species in isolation, there is a relationship between beetle length and the number of pupae they ate. If mean values are calculated for each midsized species during each sampling week, there are 52 discrete sampling events among the eight species. There is a significant effect of beetle length on the number of pupae eaten when the weekly mean values for each species are compared (F1/51 = 6.6, P = 0.01, R2 = 0.12). The fact that N. brevicaulis tends to be longer than the other beetles that ate the same number of sentinel prey suggests fly pupae may not be a favored food item for this species as well (Figure 5). When N. brevicaulis is removed from the data set there are 46 sample events and the effect of length on voracity increases (F1/45 = 12.6, P = 0.0001, R2 = 0.22).
The number of fly pupae a species would eat was not constant over the season for many species and tended to be high during periods when their activity was greatest and low when their activity was reduced (Table 2). Amara littoralis, Harpalus affinis and the spring season of N. brevicaulis are examples of where both voracity and activity density increases in the early part of the activity season and decline during the end of the activity season (Figure 8). During the fall activity season the voracity of N. brevicaulis is consistent between each month. Harpalus affinis continued to have relatively high voracity levels later in the season even after their peak activity density (Figure 8). Pterostichus melanarius is a large species which ate all of the pupae offered, so it is impossible to determine if it would have eaten more during the months with greatest activity on the landscape. There were differences in the specific pattern among other species as well, but the tendency for voracity and activity to rise or fall in tandem was observed in several species (Appendix II).
All of the ground beetle species were found to eat at least a few seeds, but there was significant variability among the species (F13/382 = 20, P < 10-15). A few species like Nebria brevicaulis and S. marginatus ate very few seeds and may have only tested the edibility of the ones that were eaten. Other species, including the two species of Harpalus and Anisodactylus binotatus, ate almost all of the seeds that were presented (Figure 7). However, even for the species that ate the highest number of seeds the proportion eaten was never much more that 0.5, indicating an equal preference for seeds and pupae. Within each beetle species the proportion of their diet that was seeds did not generally vary over the season (Table 2).
After excluding samples that were damaged by slugs, a regression identified significant effects of the abundance of certain beetle predator guilds on the number of pupae removed (Table 4). In the March through June activity period there were a large number of mid-sized beetles active in the landscape, and fewer large or small beetles compared to late summer. There were greater numbers of pupae eaten at trap sites as the number of mid-sized beetles caught in the pitfall trap increased (Figure 10). For small and large beetles there also was a significant association with the number of pupae eaten, but the number decreased with more beetles. During the July to October activity season the relationships were different. The large carabids, which were by far the most abundant group during the later season, were associated with an increase in the number of pupae eaten, but there was no relationship between the other beetle size classes and the number of sentinel prey eaten (Table 4, Figure 10). Even though the beetle species associated with the fly pupae consumption changed over the year, the seasonally pooled mean number of pupae eaten per card was relatively constant during both the spring to early summer (9.5 pupae removed) and the late summer to fall seasons (10.8 pupae removed). During the winter season when the activity of almost all of the beetle species was very low there were 2.8 pupae removed per card.
Life history timing
During the pitfall trapping there were two general peaks in ground beetle larvae activity. One peak was in the early summer and the other was in the winter (Figure 9). Ground beetle larvae were assigned to three morphological groups. The size based groups (small larvae and large larvae) included larvae of multiple ground beetle species, so there were activity peaks in both the winter and the summer. The third group was a distinctive morphospecies that was caught in large numbers within the annual crop fields throughout the winter (winter larvae).
The appearance of teneral beetles marks the emergence of adults from pupae at the end of pupation. Teneral beetles were observed in nine species, but only at one time of year for each species (Table 3). Recently emerged teneral beetles were observed in three of the large species and in each case it was early in the activity season of the species. Among many of the midsized beetle species, recently emerged adults join the rest of the population near the end of the activity season. N. brevicaulis is the exception among the midsized beetles because teneral beetles were observed during the initial activity period during the spring and not during the fall activity season (Figure 8).
The number of eggs in the females of each species varied over the season, with many species having a distinct period of egg production followed by a period of decline in the egg load. The peak in egg load coincided with the peak in activity for some species, but for others it was earlier or later in the season (Table 3).
The eggs begin the development process that continues as the larvae hatch and grow through larval and pupal stages until emergence as teneral beetles. The season of larval development can be deduced based on the peak in egg load marking the larval hatch and the observation of teneral beetles marking the end of the immature stages (Figure 8). The large beetles lay their eggs during their late summer and fall activity seasons and the larvae develop over the winter before finishing pupation at the beginning of the next activity season. Based on the abundance and timing of the “winter larvae” group, it is likely that they are larvae of large species, P. melanarius (Figure 9). Over-wintering larvae of other large beetles could be represented among the large larvae or may be small larvae if they were in an early instar.
For most of the midsize beetle species, the highest egg loads were observed early in the activity season. The observation of tenerals later in the activity season suggests that larval development of these species occurs in the summer (Figure 8). The collections of small and large larvae from the pitfall traps during the summer likely include these species (Figure 9). The midsized beetle with two activity seasons, N. brevicaulis, was only found with eggs during its fall activity season. The larvae must develop over the winter in this species before the emergence of adults during the spring activity season (Table 3).
The three native beetles most closely associated with perennial habitat types, O. audouini, S. marginatus and P. algidus, did not have fully developed wings, while the other species did (Table 3). Only around one third of the dissected Pterostichus melanarius individuals had full wings. There was a single female of each species of Anisodactylus without full wings, while the rest of the winged species had full wings in all individuals (Table 3).
Characterization of the beetle assemblages on farms in the Pacific Northwest
The seasonal phenology and habitat use of some of the species encountered on Oregon farms in this study have been documented from other regions, additionally there are congeners of species studied in other regions. (Lys and Nentwig, 1992, Niemel; et al. 1993, and Sunderland 1996, Carmona and Landis 1999, Larsen, et al. 2003). While the activity and habitat patterns of ground beetle species are influenced by relatively fixed life history characteristics, there are also behavioral responses that potentially respond to differences in climate and ecological conditions present in particular regions.
Carabid life histories are distinguished by three main traits: the time necessary for development from egg to breeding adults, the time of year when adults are active or inactive, and the maximum lifespan of a typical beetle (Matalin 2007). There are many permutations possible in these characteristics, but most species fall into one of a few main groups. With the seasonal activity information and the timing of developmental transitions as determined by the egg load and teneral beetle data, I was able to assign the common beetle species of Willamette valley farm landscapes to general life history groups. Overall, the general life history groups observed in Oregon broadly correspond with those that have been observed in other regions; however, there are some notable specific differences.
Spring active beetles
Harpalus affinis and the species of Anisodactylus, Agonum and Amara identified on Willamette valley farms are midsized beetles that have a maximum activity and egg laying season in the spring and early summer. In spring-active beetles the egg develops through larval and pupal stages over the growing season (Matalin 2007, Saska and Honek 2008). Adults emerge near the end of summer and have a diapause or similar inactive stage before the activity and breeding season the following spring. Many individuals can live for more than one breeding season as well (Kirk 1977). This means over-winter mortality of adults can have a drastic effect on population fitness and points to the importance of suitable over winter habitat for these species.
Late summer active beetles
Pterostichus melanarius is the most abundant species in Willamette valley farm fields in the late summer. It is a large European species that has become established in much of the United States and Canada. In Europe, the species has been observed to have two different life histories, with some beetles having a peak of activity in early summer and others having a peak in late summer (Matalin 2007). In the Willamette valley, the maximum activity is during August and September and peak egg load is during September. It appears that the larvae over-winter and grow the following spring and summer, and the new adults emerge again near the end of summer. Harpalus pensylvanicus is widespread north American late summer-active beetle that in some systems exhibits a peak in activity earlier in the year when over-wintered adults emerge and another peak when the over-wintered larvae finish pupation and emerge (Barney and Pass 1986). Other large beetles, including the pacific Northwest natives P. algidus and S. marginatus, have eggs in the late summer and fall and larval development over the winter and spring. These species breed soon after emerging from pupae, but they can live a multiple years so a number of adults of these species are likely to need over-wintering habitat.
Other life history groups
Among the beetles encountered in this study the seasonal activity groups largely correspond with the size class groups, with mid-sized beetles active in the spring and large beetles active in the late summer and fall. However, a few of the beetle species had life history characteristics that differed from other species within their size group. N. brevicaulis is a midsized beetle that produces eggs in the fall, while Omus audouini is large beetle that is active in the spring.
Nebria brevicaulis has an activity season in the spring, slightly earlier than the other midsized species, when adults emerge from pupae. During the activity season in the fall females produce eggs. Their life history is similar to spring active beetles in that there is a period of aestivation between when adults emerge from pupae and when the breeding season begins, except for N. brevicaulis the inactive period is in the summer while in the other midsized beetles it is in the winter. The inactive beetles have been shown to congregate in hedgerows during the summer aestivation, similar to how the spring-active beetles shelter in grassy habitats for the winter (Fernandez-Garcia 2000). The bi-modal activity season has been observed in N. brevicaulis populations in its native range (Penney 1969). Lab experiments have identified the seasonal changes in photoperiod as being a driver of sexual maturation in N. brevicaulis and another species of Nebria (Penney 1969, Telfer and Butterfield 2004). Photoperiod may influence the maturation of the spring breeding beetles too, but it could also be signaled by cold winter temperatures, or higher temperatures may simply allow development to proceed (Theile 1977).
Omus audouini is a large, Northwest native species which is active from April to July. This is much earlier that the other large beetles in this study. Although it is included as a ground beetle here, it is not taxonomically in the ground beetle family (Carabidae), but rather in the closely related tiger beetle family (Cicindellidae). Teneral individuals were not observed so the larval development season cannot be fully delimited. The taxonomic differences between tiger beetles and carabids mean this species may belong to its own life history group. The fact that it did not eat many fly pupae suggest that it may not have the same effect on risk to a potential prey items as the other large beetles in the predator guild.
Habitat use on farms
Beetle activity was highest within the crop fields for most of the species described here. This result is similar to results from other regions for P. melanarius, which has been shown to have reduced activity in habitats dominated with perennial grass and near field edges (Carcamo and Spence 1994, Tuovinen, et al. 2006, Hajek, et al. 2007). An. sanctaecrucis also has been associated with tilled crop fields in other studies as have both Ag. muelleri, and other species of Agonum from other regions (Esau and Peters 1975, Hatten, et al. 2007, Anjum-Zubair, et al. 2010). H. pensylvanicus was collected in higher numbers in mowed than un-mowed sites, suggesting that the attraction to more disturbed sites may be associated with the amount of vegetative cover (Crist and Ahern 1999).
Other studies have shown different results, with some of these species being less abundant in crop fields than other habitats. In a comparison of trap catches of seven species of Anisodactylus in a Iowa cornfields, fencerows and prairie, around 80 percent were caught in the fence row, while the prairie had around 15 percent and the corn had only a few collections (Esau and Peters 1975). An. californicus from Idaho was caught in no till fields but not in conventionally tilled fields, although there were few collections overall (Hatten, et al. 2007). Several species of Amara from Iowa were most abundant in the fence row, while one species was most abundant in the corn and another species was most abundant in the prairie (Esau and Peters 1975). Am. californica from Idaho showed no differences in activity between tilled and un-tilled dry land grains, although there were few collections overall (Hatten, et al. 2007). In Oklahoma, H. pensylvanicus was most abundant in the riparian areas adjacent to wheat fields and least abundant within the wheat fields (French and Elliott 1999). In other studies, P. melanarius was found to not be associated with tilled agricultural fields (Clark, et al. 1997, Hatten, et al. 2007).
Ground beetle activity may be driven by many factors. The discrepancies between studies may be influenced by the difference in moisture levels within fields and in field margin habitats depending on the local rainfall pattern and irrigation regime. Midwestern farms receive a significant amount of rain over the growing season that is distributed to all the habitats on the farm. On farms in the Northwest, the soil moisture levels get very low during the late summer, except in crop fields where supplemental irrigation keeps the soil moist throughout the season. If beetle activity patterns are limited by soil moisture levels, beetles would be more likely to be found in field margins of farms in areas with summer rain than in areas dependent on irrigation. Pesticides can be another factor if their application drives beetles out of their preferred habitat in tilled fields to refuges like fence rows.
Beetles with inactive periods such as winter hibernation or summer aestivation will move between the crop fields and other habitats that provide better shelter. This is clearly shown in the greater number of soil core collections from perennial than annual vegetation patches. Extensive trapping regimes can also document populations as they move into and out of their aestivation sites (Fernandez-Garcia 2000). The soil core samples contained primarily immature beetles belonging to the spring activity group that emerge from pupae at the end of summer. There were also mature adults that were experiencing an additional winter.
There were three common species which were primarily associated with perennial habitats during their activity seasons: P. algidus, S. marginatus and O. audouini. A study of different habitats on a tree farm in southwest Washington found similar results (Johnson, et al. 1966). In that study, P. algidus and a different species of Omus (O. dejeani) were caught in higher numbers in an open forest of Douglas fir and perennial grass than in a recently clear cut site with bare soil and pioneer vegetation (Johnson, et al. 1966). This differed from a species of Scaphinotus (S. angusticollis Fisch.), which had high numbers in the young forest and the recent clear cut, and low numbers in the grassy open forest (Johnson, et al. 1966). This suggests that the S. angusticollis is not simply responding to the forest cover, but perhaps the woody debris that remains after the harvest.
Three additional large beetle species were only rarely caught, and when they were caught they were in the same or adjacent traps each time. Metrius contractus Esch. was caught in the same forested area where S. marginatus was caught. Blethesia multipunctata Fisch. was only caught on the margin of seasonal pond with shrubs and emergent aquatic plants. A single collection of O. dejeani was made from a wide grassy road between the field and a mature forest. These species also are likely to be associated with particular habitats on the landscape but were too rare to draw any strong conclusions.
Feeding characteristics and impact on risk of predation of potential pests
Most of the beetle species observed in this study readily ate the freeze killed fly pupae and the A. retroflexus seeds, but a few species did not. These species likely have prey preferences that were not well represented by the fly pupae or seeds used in the study. Scaphinotus marginatus has a unique head morphology that suggests it is a specialist on snails and mollusks. In one instance an individual of the tiger beetle, O. audouini, was presented with a leafroller (Lepidoptera: Tortricidae) caterpillar which was live and moving around. The beetle immediately attacked and began consuming the caterpillar, suggesting it may prefer active or larger prey to the freeze killed fly pupae used as sentinel prey in this study. The putative diet of N. brevicaulis is Collembolans and other small arthropods, and that may explain why individuals ate fewer pupae than other midsized beetles (Penney 1969, Warner, et al. 2008).
The per capita pupae consumption rate was correlated with the mean length of females of the beetle species. Smaller species, like beetles in the Amara genus, tended to eat fewer pupae than the larger species. The largest species tended to eat all of the prey items presented, making it likely that their calculated mean per capita pupae consumption rate is an underestimate. Per capita pupae consumption rate tended to rise and fall along with the seasonal activity patterns of the beetles. The activity density estimate provided by pitfall trapping is insufficient by itself to estimate population density (Topping and Sunderland 1992, Lang 2000, Thomas, et al. 2006). If greater activity is associated with increased food consumption, it supports the notion that the pitfall traps can be a good measure of the amount of foraging that beetles are doing in the field.
Species of Harpalus and Anisodactylus from the Willamette valley consumed a high number of seeds in this study. Species from other regions have been shown to consume seeds as well (Johnson and Cameron 1969, Lund and Turpin 1977, Honek, et al. 2006, White, et al 2007, Sasakawa 2009, Sasakawa 2010). In this study the two species of Amara consumed seeds. Species of Amara from other regions have varied in the types and amounts of seeds eaten (Klimes and Saska 2010, Saska 2005, White, et al 2007, Sasakawa, et al. 2010). Pterostichus melanarius and three species of Agonum from New York State were observed feeding on seeds in the lab (Johnson and Cameron 1969). Pterostichus melanarius from the Willamette valley ate a large number of seeds, while the species of Agonum were found to eat some seeds, but relatively fewer than other tested species. Although most species did eat seeds, no species ate many more seeds than pupae. This suggests that these species may be foraging on both weed seeds and insect pests when they are active in the agricultural fields. Any estimate of the effect of ground beetles on a single pest species would undervalue their importance, as these generalist predators may play a role in mortality for multiple agricultural weeds and pests.
Ground beetles were assigned to three predator guilds based on body size (small, midsized, and large beetles). Beetles can easily be grouped into a size class just by observation in the field so all of the species encountered could be classified. Among the species collected here, size is also an effective stand-in for a number of other beetle characteristics that influence their predation activity. Larger beetles tend to eat more sentinel prey items than the medium sized beetles, and small beetles are likely to eat even less. If the sentinel prey is widely acceptable among other ground beetle species, size class should be a good way to classify species based on how much prey they consume. Size can also group the species encountered in this study based on when they are likely to be actively searching for prey in the field. Large beetle populations were dominated by species that were active in the late summer or fall and had larvae that developed over the winter. Mid-sized beetles were dominated by species that were active in the spring and early summer and had larvae that developed over the summer (Table3). This means that for the species in this study, grouping by size class identifies guilds of generalist predators that have a similar response to the environment and a similar effect on prey communities. Species within each guild act together to increase the overall predation risk that a potential prey item faces in the field.
The field pest predation risk as measured by the sentinel prey was related to the activity of the common beetles in this study. The two strongest correlations between sentinel prey consumption and beetle activity density were with medium-sized beetles in the spring and large beetles in the summer. These are the periods that these groups are most active in the field and when they will eat the most food in the lab. There is no direct evidence that the reduction in sentinel prey was caused by the beetles that were sampled with the pitfall traps. The slug damage points to a number of possible fates for the sentinel prey items. This is reflected in the relatively low correlation coefficients of the regression models (adjusted r2 = 0.01 for both equations). Despite the low explanatory power, the fact that the significant positive relationships were identified between the most abundant carabid group of the season and sentinel prey removal rate suggests that these species are consuming a significant number of potential crop pests during the seasons that they are the most active. Also the data suggest that prey consumption is relatively equal throughout the season even though the beetle species doing the consumption change.
Implications for conservation biological control
The value of carabids in conservation biological control depends on the extent to which they increase the risk of predation for a pest organism. Both the phenology of when a potential pest is vulnerable to predation by carabids and the activity season of the carabid will determine if a species can play a role in controlling the pest (Warner, et al. 2008). In this study, the overall predation risk faced by potential prey items was maintained at a relatively constant level throughout the season by a diverse range of beetle species with distinct life histories. Seasonal activity cycles and habitat use are driven by the biology of each species. Knowledge of insect life histories makes it possible to identify the species present on a farm and make predictions about which carabid species may be important predators of specific pests. Information about habitat use may also make it possible to predict which species from the local pool may be rare or missing from a site and to evaluate the potential impact on biological control. Appropriate modifications can be made to the landscape or management practices to encourage population growth of the target species.
An example of this approach is illustrated by considering the potential for ground beetle assemblages to control the Cabbage looper (Trichoplusia ni). The Cabbage looper is a pest of cabbage and related crops. The larvae move between the vegetation and the soil at the base of the plant, where they are vulnerable to predation by carabids. In the Pacific Northwest there are two generations per year (Berry 1998). When mean daily temperatures for Corvallis, Oregon are used to calculate degree day accumulation, a phenology model for Cabbage looper predicts larvae will be present in June and August. The August caterpillars are at risk from the late summer active beetles group, particularly P. melanarius, the most abundant species on each farm (Figure 11). Pterostichus melanarius is adapted to the conditions of annual crop fields and is common even on heavily managed farms. The spring-active species vary in the relative activity density between farms. On farms with lower relative numbers of spring active beetles (farms P and K), the number of potential predators and the associated risk for predation on the June caterpillars is low relative to the number of predators in August (Figure 11). Enhancing the populations of the spring-active beetle species through conservation biological control is one potential pest management strategy.
There needs to be further research to identify the critical factors that drive the observed differences in populations, but an understanding of the life histories of these beetles points to some possible ways to encourage their populations. The spring-active species emerge at the end of summer and must find a place to hibernate for the winter. The beetles are primarily found hibernating in perennial grassy areas. If these types of hibernation sites are limiting populations, including more grassy areas in the landscape, it could result in larger beetle populations (Griffiths et al. 2008). Other factors such as the availability of weed seeds as a larval food supply or refuge from tillage or pesticides may also be important (Hartke, et al. 1998, Sasakawa 2009). When necessary resources are identified, simple methods for providing those resources can be devised and communicated to farm managers who wish to benefit from the services of these species.
This project has greatly improved our understanding of the ecological dynamics of ground beetle assemblages in the Pacific Northwest. In particular we have a clearer picture of how the activity of whole beetle assemblages combine to provide potential pest control services on farms. This information is being used by farmers to create and enhance conditions on their farms that will maximize the pest control services provided by ground beetles. We expect that the formal and participatory dissemination of the information that this project facilitated will increase the adoption of these practices on farms throughout the region. The project has had specific impacts in each of the core focus areas of the project:
1. The project developed the first comprehensive description of beetle assemblages on farms in the Pacific Northwest. Prior to this project much of the basic biology of beetles on farms in the region was either not known or had to be inferred from studies conducted on similar species in other regions. The information generated by this project is now an extremely valuable resource for future researchers
2. The project demonstrated the value of both planned and unplanned habitat in the form of perennial grass and less disturbed vegetation for maintaining beetle assemblages on farms. The work confirmed the efficacy and value of maintaining and enhancing these habitats on farms. While a handful of other studies conducted in the region have also demonstrated the potential value of these habitats for ground beetle populations, this project produced the first results for the region that documented these relationships at the scale of entire farm landscapes and over the course of several years. This has greatly improved our understanding of the spatial and temporal dynamics of ground beetle assemblages on farms in the region.
3. The project showed that the biocontrol potential of ground beetle assemblages on farms in the region is dependent on having a diverse range of beetles that include species groups that are active both early and late in the season. The project showed that one of the important consequences of reduced habitat quality on farms is a loss of the early season guild that leaves farms with reduced pest suppression capacity.
4. The research contributions described above were communicated to researchers at several national scientific meetings and are in the process of being submitted to several scientific journals.
Education and outreach
1. The project supported the education of one Ph.D. student and provided research experiences for two undergraduate students. We expect all three to make significant contributions to sustainable agriculture as their careers progress.
2. The project increased the knowledge and awareness of farmers in the region to the value of ground beetles and their habitat needs (see publications and outreach). Through the education and outreach products described below, we introduced farmers to the ecology, biology and potential ecological services that predacious ground beetles provide farms. We also familiarized farmers with the types of habitats that foster beetle activity, as well as the concept of creating habitat to promote predaceous ground beetles and other beneficial arthropods. The project events helped over 136 farmers and other participants evaluate their farms in terms of beetle habitat and plan strategies for enhancing this habitat on their own farms. The research results from our project improved our ability to make more specific recommendations about the types of habitat that will attract specific beetle species, as well as the potential impact this will have on pest suppression within production fields.
Educational & Outreach Activities
This project produced (and will produce) a number of publications, presentations and outreach events.
Russell, M., Lambrinos, J.G., Ellen, G. In preparation. Habitat types, plant species and vegetation characteristics associated with high densities of over wintering predatory beetles and spiders in western Oregon vegetable farm landscapes.
Russell, M., Lambrinos, J.G., Ellen, G. In preparation. Seasonal activity and feeding patterns of Ground beetles (Carabidae: Coleoptera) in a western Oregon agricultural landscape.
Ellen, G., Russell, M , Lambrinos, J.G. In review. Encouraging predacious ground beetles on Willamette Valley farms. Oregon State University Extension Service.
Russell, M. 2013. Habitat management for beneficial insects on Willamette Valley vegetable and berry farms. PhD. Dissertation. Oregon State University
Greco, A., Russell, M*., Green, J., Moulton, L., & Peachey, R. E. 2012. An introduction to ground beetles of the Willamette Valley. Oregon State University Extension Service. http://extension.oregonstate.edu/catalog/html/em/em9042/
*publication was produced in cooperation with another NIFA-funded project. M. Russell was funded under this Western SARE project and provided data produced under this project.
Ellen, G., M.C. Russell, J.G. Lambrinos. 2012. Building a regional network for linking science, policy, and practitioners to enhance biodiversity in agricultural ecosystems. Annual Meeting Ecological Society of America, Portland OR.
Russell, M., Lambrinos, J.G., Ellen, G. 2012 . Carabidae in conservation biological control: the distributions, activity patterns, and feeding habits of common western Oregon ground beetles, and their relation to pest predation risk across agricultural landscapes. Ecological Society of America Annual Meeting,8 August, 2012, Portland, Oregon
Russell, M. 2011. Seasonal Activities and Feeding of Ground Beetles in Western Oregon Agricultural Landscapes. Pacific branch of the Entomological Society of America Annual Meeting, 28 March, 2011, Waikoloa, Hawaii.
Russell, M. 2010. A functional approach to understanding species utility for conservation biological control : the relative value of six grass species for moderating soil surface temperatures and providing over wintering habitat for generalist predators. Ecological Society of America Annual Meeting, 4 August, 2010, Pittsburgh, Pennsylvania.
Integrating Beetle Habitat into Pacific Northwest Farming Systems
Banking on Beetles in Oregon
Education and Outreach programs
We collaborated with our participating farmers through several grower-researcher meetings, on-farm demonstrations of research activities and field classes. Agendas, handouts and printed presentations that were provided to participants at each event are provided as supplemental information.
1. A winter project meeting at farmer cooperator Brad Bailie’s Lenwood Farms in Connell, Washington on 12/8/09. We discussed his project goals and role, current farm habitat, plans for future habitat, 2010 project sampling for predacious ground beetles and a 2010 farm walk at his farm were discussed. We visited two already established beetle banks of rye and various non-native grasses and one new bank testing native Columbia basin grasses of sand dropseed, Idaho fescue, blue bunch grass and basin wild rye. Brad’s goals for this project are to learn more about what effects these insectary plantings are having on his farm in terms of crop pest management, and what new techniques can he employ to better manage the insectary plantings.
2. A winter project meeting with the four Oregon farmer participators in January 2010. We discussed and planned project goals, roles, current farm habitats, future habitat plans, 2010 project sampling schedules for predacious ground beetles and a 2010 farm walk. It was decided that the Oregon farm walk would be in July at Persephone Farm in Lebanon, OR. Persephone Farm is home to two beetle banks, one which is four years old, and two in field hedgerows. The Oregon farmers’ project goals are identical to Brad’s goals in Washington. With the exception of Peter Kenagy of Kenagy Family Farms, who already has extensive mature insectary and conservation plantings on his 360 acre vegetable farm, all have plans to create new insectary plantings in addition to their current on-farm habitat.
3. A farm walk and short course on Lenwood Farms in Connell, WA, June 23rd, 2010 (Fig. 12). This course was jointly sponsored by this project, Lenwood Farms and the Western Region Conservation Biological Control Work Group, farmer generated industry funds, and in-kind contributions from the USDA, NRCS, Plant Material’s Center of Corvallis, OR, the National Center for Alternative Technology (NCAT) California Office, the Integrated Plant Protection Center, OSU, the Pollinator Program for Xerces Society for Invertebrate Conservation, Portland METRO’s conservation program and WA’s Sound Horticulture. The walk, called the 2nd Annual Biodiversity Working for Farmers Tour/Short Course, was attended by over 120 area farmers, industry representatives, extension researchers, conservation agency personnel, one WA Senator and various city and county representatives.
Lenwood Farms is a 600 acre certified organic potato, pea, squash and grain farm in the Columbia Basin. Ten invited speakers and four FAB Work Group speakers, including members of this project, used the farm as a teaching laboratory. We presented information and early results from this project’s on-farm research, as well as other research being conducted on the farm examining the relationship between habitat diversity and ecosystem services. The short course program also included a discussion of issues and policies that hinder and support local conservation practices and organizations that aid in their implementation and adoption.
The 2010 Tour/Short Course at Lenwood Farms included a dynamic farmer panel with four local farmers (including Senator Mark Schoester who farms over 12,000 acres of dryland wheat), this project’s Gwendolyn Ellen, and the executive director of Organically Grown Company (OGC), which buys Lenwood Farms produce. The panel discussed the potential role that on-farm biodiversity enhancement and conservation practices could play in improving farm income and sustainability, as well as some of the constraints that may limit the potential for the full benefits of these practices to be realized. The panel specifically addressed ways to foster better cooperation and communication between regional farmers, researchers and government agencies.
We created a press release of the farm walk/course that resulted in extensive media coverage. Articles went out in many WA and other Pacific Northwest newspapers. An article about our program was even reported on an Asian agricultural blog. An article highlighting the conservation practices on Lenwood Farms was published in the October 2010 issue of the American Vegetable Association.
4. A combined winter project meeting and field class held 2/25/2011 in Corvallis, OR. This meeting included one additional farmer not directly collaborating on our project who was interested in hearing our results and getting recommendations for installing habitat. Similar to our previous project meetings, we shared with participating farmers the results of our field work, planned upcoming work and analyses, and planned the location and format of our summer field course.
5. A farm walk and short course held 9/1/2011 on Gathering Together Farm, Philomath OR (Figure 13). The course was titled Assessing Beneficial Insect Habitat on Your Farm: A Predacious Ground Beetle Example and attracted 15 participants that included farmers, farm personnel and government agency representatives. The course used our established model of active learning and collaborative participation described in the proposal and the previous annual report. Part of the course involved a habitat mapping exercise to train farmers in identifying existing beneficial predator habitat as well as gaps where improvements in habitat could be useful. During this exercise we trialed a draft habitat assessment worksheet (Appendix III); development of this worksheet was one of the outreach goals of our project. We also elicited feedback from participants on this worksheet, as well as on other ways conveying practical information to farmers. The habitat mapping process (and overall class) was informed by findings developed in the research component of our project.
6. All the participating farmers in our project led various tours and gave several presentations to a broad audience of farmers, students, agricultural professionals and consumers over the course of the project. Many of these presentations were not specifically related to implementing ground beetle habitat on farms, so we do not list them specifically as products of our project. However, at these events our participating farmers served as invaluable ambassadors for the project and served as peer educators for the important services that beneficial beetles can provide for farmers.
An economic analysis was not an objective of this project. However, in our previous Western SARE-funded project (FW06-324) we generated cost estimates for implementing beetle bank habitat. The four foot wide banks that were established in that study cost approximately 3-6 dollars/linear foot to install (including plant materials and labor). In addition, the most costly and labor intensive factor in establishing beetle banks in organic systems was weed management. In some cases, weed management in the first few years following installation could double the overall cost.
The results of this study suggest that many vegetable farmers in the region could maintain sizeable and diverse ground beetle assemblages on their farms simply by maintaining the existing habitat they already have on their farms. Existing habit in the form of grassy field margins, fallow grass fields and natural areas such as riparian zones provided significant habitat for the beetles on the farms we studied. Maintaining existing habitat for beetles could be a significantly cheaper alternative to installing new habitat in the form of beetle banks. In fact, changes to management practices that could enhance the value of these habitats for ground beetles, such as reduced mowing or herbicide use, could reduce overall direct management costs for farmers.
However, some anecdotal evidence suggests that our project spurred farmers in our region to include ground beetle habitat management as an explicit component of their farm management plans. We interacted with about 150 farmers at our outreach events. Several of these farmers indicated that they were going to change their management practices or install a beetle bank based on information they had learned at the event. In addition, just prior to the start of the project, we were aware of about 15 farmers who had installed specific beetle habitat on their farms. Over the course of this project, we heard of at least 30 more specific instances. In part, this undoubtedly simply reflects our increased encounters with interested farmers as a result of our outreach events. However, we suspect it also reflects a genuine growth in farmer adoption. The habitat we know about likely represents a small fraction of the actual habitat that has been implemented or that is actively being maintained.
A significant finding of this project is that many vegetable farms in the region already have potentially suitable habitat for ground beetles. Many farmers can markedly improve habitat conditions on their farm by making relatively simple adjustments to their management. These include reducing mowing frequency in perennial grass habitats and minimizing herbicide drift onto adjacent field margins. On farms where field size is large or perennial habitats are minimal, such as is the case for many center pivot-irrigated farms in eastern WA and OR, the creation of habitat in the form of beetle banks may be necessary to maintain beetle activity within fields.
Areas needing additional study
One important next step to integrating beetle habitat into Pacific Northwest farming systems would be to develop automated tools for assessing beneficial habitat on farms. The models and outreach tools we developed as part of this project still required detailed evaluations in the field. The farmers who participated in our outreach events received detailed and specific recommendations for maintaining and improving habitat on their farms. Our extension publications and website make some of this information available to a wider audience. However, the information delivered via these approaches is necessarily more generic and does not provide detailed farm and farmer specific recommendations.
One approach to providing detailed site specific recommendations to a larger number of regional farmers is to combine the habitat models we developed in this project with remotely sensed data using web based-tools. Vegetation models derived from LiDAR are at extremely high spatial resolution, potentially making it possible to use these data to develop detailed structural habitat maps of individual farms. As the spatial and temporal coverage of LiDAR and other pertinent datasets increase, it may be possible to develop near real time estimates of beneficial insect habitat across entire regions. Using these data to parameterize versions of the habitat models we developed could allow us to automatically and remotely produce detailed and accurate habitat quality assessments for any farm within a region. Integrating this system with a web-based user interface could deliver this information directly to farmers, empowering them to make individual decisions about their habitat management.
Another research area needing further study is the degree to which the predation provided by beetle assemblages actually regulates pest populations in the field. This is a difficult question to answer, and it is one that has lingered in the field of biological control since its inception. Our study demonstrated that the predation risk face by potential prey items was related to beetle activity on our study farms. This risk varies seasonally and with the specific species composition of beetles activity on any particular farm. However, we cannot say that this risk (or the variation in risk) causes changes in the actual abundance of pests. Demonstrating this relationship in actual field setting would require long-term field-scale experiments.