Carabid (Coleoptera: Carabidae) biology within diverse agricultural systems of the Southern Great Plains is not well studied. This study was conducted to elucidate carabid dispersal powers, colonization rates, habitat utilization, natal origins, and the impact of tillage on carabid populations in diverse agroecosystems. The effects of tillage regimes and colonization rates from a semi-permanent habitat into an annual cropping system were investigated with standard pitfall trap sampling. Carabid dispersal powers, habitat utilization, natal origins, and diet switching were determined by stable carbon isotope data. For 2006, the average number of carabids per trap in no-till (NT) and conventional till (CT) was similar in Period 1. During Period 2, these averages decreased in no-till and increased in conventional tillage. The differences in the availability and distribution of resources and the density of ground cover in NT and CT impacted carabid foraging activity-density which altered the opportunities for carabids to be trapped. Data analysis for 2007 tillage impact is in process. Colonization data has provided fine scale resolution to beetle movement into the annual cropping system from the semi-permanent habitat. Stable carbon isotope data for 2006 and 2007 show that 631 carabids moved from alfalfa to sorghum and 61 moved from sorghum to alfalfa. This data revealed that there were a total of 305 carabids that did not move from alfalfa and 29 did not move from sorghum. Natal origins were determined for 505 carabids in 2006 and analysis continues for the rest of 2006 and 2007. Dieting switching was confirmed for a total 28 carabids based on stable carbon isotope ratios of the P and R tissue sub-samples from each beetle.
This study has provided information to producers regarding carabid colonization and dispersal abilities in diverse agroecosystems. Tillage and dispersal data demonstrates that alfalfa is utilized as a refuge habitat by carabids during catastrophic environmental disturbances. Isotope results from the selected P and R sub-sample tissues have shown a high degree of resolution for determining movement and diet switching for individual beetles. This data supports the need for diversifying agroecosystems to provide carabids with the various habitats necessary to complete all life stages. Carabid mobility and polyphagous feeding habits demonstrate the need to conserve these biological control agents within the agroecosystems of the Southern Great Plains.
In the Southern Great Plains, natural enemies have a regulating effect on pest populations in winter wheat, alfalfa, cotton, and sorghum (Kring et al. 1985; Rice and Wilde 1988; Giles et al. 2003). This natural regulating effect is an essential component of integrated pest management plans (IPM). Holland et al. (2005) considers carabids one of the most important ground-dwelling consumers of agricultural pests. Carabids are excellent organisms to study in agroecosystems because they react to environmental changes quickly and measurably (Thiele 1977; Fournier and Loreau 2000; Holland et al. 2005). This is due to their reproductive plasticity and flexible behavioral and environmental requirements (Thiele 1977; Holland 2002). These beetles are relatively easy to sample due to their foraging techniques and dispersal characterized by walking rather than flying (Thiele 1977; Fournier and Loreau 1999). Carabids are often abundant and persistent despite catastrophic disturbances in agroecosystems (Thiele 1977; Lövei and Sunderland 1996). Integrated pest management (IPM) practitioners readily recognize the polyphagous nature of carabids and the potential implications of this feeding activity on the consumption of pest species. However, carabid biology within diverse agricultural systems of the Southern Great Plains is not well studied.
Monoculture crops dominate farming practices in the prairies of North America and monocultures can lead to an increase in pest pressures (Elliott et al. 1998; Ahern and Brewer 2002; Brewer and Elliott 2004; Boyles et al. 2004; Men et al. 2004; Ribas et al. 2005). These homogeneous crops increase the isolation and fragmentation of suitable habitats for natural enemies. Predators are generally thought to be more vulnerable to fragmentation of habitat than prey species (Kruess and Tscharntke 1994; Abensperg-Traun and Smith 1999; Kruess and Tscharntke 2000). This vulnerability can be expressed as a breakdown in food chains and loss of trophic structure within ecosystems (Hunter 2002). Additionally, habitat degradation and limited resources within these monocultures can diminish the ability of natural enemies such as carabids to decrease pest populations leading to a loss of crop and forage yields (Lys 1994). For example, yield loss and insecticide costs from an outbreak of greenbug, (Schizaphis graminum) can range from $3.8 to $135 million in grain wheat grown in Oklahoma (Webster 1995). The greenbug can reproduce rapidly often without detection and reach economic injury levels quickly (Starks and Burton 1977). Alfalfa, grown for livestock forage, can produce gross incomes exceeding $100 million for Oklahoma producers and over 480,000 tons annually for Texas alfalfa producers. Alfalfa suffers reduced quality and yield losses from attacks by alfalfa weevils, spotted and blue alfalfa aphids, pea aphids, defoliating caterpillars, and army cutworms (Cooperative Extension Service 2008). Oklahoma and Texas producers plant over three million acres in sorghum annually with an estimated cash value over $315 million dollars, however; this amount exceeds $1 billion when used as livestock feed (NASS 2005). Sorghum producers are also plagued by insect pests, such as greenbugs, and weed encroachment.
Producers have used insecticides to address some pest problems; however, use of these products can cause a breakdown in the life cycle of natural enemies. This breakdown can lead to pest resurgence episodes that require additional insecticide applications, which increases input costs and can cause a greater risk of insecticide resistance in pests. In an effort to reduce the negative effects associated with monocultures and increase net profits, some producers are diversifying their agricultural systems (Brewer and Elliott 2004; Keenan et al. 2005). The concept that diversification of agroecosystems increases and maintains natural enemy assemblages, which in turn increases the efficiency of these biological control agents, is supported by growing data (Parajulee and Slosser 1999; Guerena and Sullivan 2003; Brewer and Elliott 2004). Carabids constitute a major part of the fauna and are an important part of the natural enemy assemblages in agroecosystems (Fox and MacLellan 1956; Rivard 1964, 1965, 1966; Whitcomb and Bell 1964; Frank 1971; Kirk 1971; Esau and Peters 1975). Carabid richness has been positively correlated to small-scale landscape heterogeneity (Weibull et al. 2003). More complex habitats supply carabids with the necessary resources to maintain higher populations allowing colonization of crops before pest species reach economic damage levels (Hunter 2002). Diversity provides increased habitat richness, which increases the abundance and persistence of predators of agricultural pests and consumers of weed seeds. Carabids consume insect pests and weed seeds; however, carabids need a variety of habitats to complete their life cycles, including feeding grounds, breeding habitats, and over wintering refuge. Because carabids react to environmental changes quickly and measurably they may also be useful as bio-indicators as well as biological control agents (Thiele 1977; Norris and Kogan 2000; Fournier and Loreau 2002; Holland et al. 2005).
With the prevalence of monocultures, producers also combat the issue of increased weed production and ultimately weed seed production (Keenan et al. 2005). Carabids are an important consumer of weed seeds due to their polyphagous nature (Lund and Turpin 1977; Thiele 1977). Genera like Amara and Harpalus have species that selectively consume weed seeds once they fall from the parent plant to the ground. This consumption of seeds can have a major influence on seed survival and therefore on plant community composition (Tooley and Brust 2002). In agroecosystems, carabids and rodents are considered the two major weed seed predators (Brust and House 1988; Marino et al. 1997; Westerman et al. 2003). In the Central Great Plains, weeds such as volunteer rye, downy brome, and jointed goatgrass, negatively impact profitable winter wheat production (Lyon and Baltensperger 1995).
Producers need more information regarding carabid feeding behavior and its impact on pest populations in diverse systems. Additionally, producers need a better understanding of carabid dispersal and colonization abilities so that they can integrate carabids into IPM plans and habitat management decisions. Carabids have long been identified as biological control agents in scientific literature; however, recognition of carabid beetles as an important component of natural enemy assemblages is lacking among producers. As producers move toward no-till diverse agricultural systems in an effort to reduce input costs and increase net profits, it is essential that they understand the impacts of these changes on pests and natural enemies. Coupled with this diversification, a reduction of pesticide use within these systems will decrease environmental contamination and protect natural enemies, like carabids, from unnecessary mortality. A reduction in disturbance regimes such as conventional tillage will decrease carabid mortality and increase their effectiveness as biological control agents. By changing farming practices, reducing the use of broad-spectrum pesticides, and diversifying agroecosystems the economic and ecological sustainability of farms in the Southern Great Plains will be improved.
Carabid distribution is affected by abiotic factors such as soil pH, soil type, and soil moisture (Baker and Dunning 1975; Hengeveld 1979; Gruttke and Weigmann 1990; Holland et al. 2007). Evidence suggests soil moisture has the greatest influence on carabid distribution (Holopainen et al. 1995; Sanderson et al. 1995; Luff 1996). Soil composition may influence microhabitat selection for oviposition and larval burrowing (Holland and Luff 2000). Larvae have higher survival rates in moist soils and are sensitive to soil temperatures (Luff 1994; Holland 2002). Adult carabids of arable lands are susceptible to water loss and are dependent upon microhabitats for added protection from desiccation.
Carabids frequently show aggregation patterns of high and low densities based on vegetation canopy, structure, and density (Speight and Lawton 1976; Hengeveld 1979; Cárcamo and Spence 1994; Holopainen 1995; Thomas et al. 1998; Holland et al. 1999). Carabids have been found in higher numbers in weedy crops. For example, no-till fields encourage weeds thereby increasing organic material on the soil surface altering microclimates (Speight and Lawton 1976; Purvis and Curry 1984; Powell et al. 1985; Kromp 1989; Pavuk et al. 1997). The amount of crop canopy present over time may influence changes in carabid assemblages by retaining more moisture as the canopy closes. All of these environmental factors alter resource and habitat availability to all carabid life stages and ultimately leads to discrete distributional patterns within and among fields (Holland and Luff 2000; Thomas et al. 2002).
Soil cultivation is another factor that can kill or disturb carabids at all life stages. However, which life stage is most at risk remains unclear. Several reviews on farming practices have described a reduction in abundance and diversity of carabid assemblages due to deep tillage (Thiele 1977; House and All 1981; Luff 1987; Stinner and House 1990; Kromp 1999; Holland and Luff 2000). It has been reported that deep soil cultivation with a moldboard plough had a negative effect on carabid abundance compared to shallow cultivation (Dubrovskaya 1970). This finding was supported by Stassart and Grégoire-Wibo’s (1983) analysis of pitfall data over several years in Belgium where they determined the depth of tillage was a major factor affecting field carabid fauna.
It has been noted that carabids are an important component of natural enemy assemblages consuming agricultural pests. Through the use of stable carbon isotopes the relationship of carabid dispersal and dietary intake over time can be better understood (Teeri and Schoeller 1979; Boutton et al. 1983; Peterson and Fry 1987; Wada et al. 1987; Harrigan et al. 1989; Ostrom and Fry 1993). By determining the differences in isotope ratios between predators, prey, and host plants within agroecosystems the dispersal of carabids can be traced among habitats (Ostrom et al. 1997; Hobson et al. 1999). This dispersal information demonstrates seasonal habitat utilization by carabids as larvae and adults (Ostrom et al. 1997; Hobson et al. 1999). Ratio data can clarify which habitat type, feeding grounds, breeding habitats, over-wintering refuge, and non-cultivated refuge, larvae and adult carabids utilize. The use of stable carbon isotope ratios (SCIR) reflects dietary information over time determining carabid prey selection and dispersal power (Peterson and Fry 1987; Hobson and Clark 1992). By understanding the environmental requirements of carabids, their presence in diversified agricultural habitats can be enhanced.
Isotope Definition and Measurements:
Elements exist in nature as one or more isotopes. Isotopes are defined as atoms of the same element which have the same number of protons and electrons but different numbers of neutrons. These isotopes will have the same charge but different masses. It is this difference in mass that can be exploited for scientific study and since their discovery in the 1920’s, ecological and biological studies have been using isotopic compositions at an increasing rate.
Fractionation is the term applied to isotopic variance and defined as the enrichment or depletion of a heavy isotope relative to a light (low mass) isotope (Broecker and Oversley 1976; Tieszen and Boutton 1989). Fractionation is the proportional difference between the isotopes’ masses. These proportional differences represent very small changes in the physical and chemical properties of each isotope within tissues (Park and Epstein 1960; Broecker and Oversley 1976; Ehleringer and Rundel 1989). Enzymatic discrimination within tissues is the utilization of one isotope and not the other or the use of one isotope before another isotope (Ehleringer and Rundel 1989). Isotopic composition absolute values can be measured accurately within a sample over the short-term; however, reliability over the long term is questionable (Hayes 1983). To provide high accuracy and repeatability over time, differences between a standard and sample must be measured (McKinney et al. 1950; Ehleringer and Rundel 1989). Differential analysis has been a standard procedure in isotope compositions since its introduction (McKinney et al. 1950). The reference material for carbon was the carbon found in the PeeDee limestone (belemnite, PDB); however, this material is now depleted. The current standard for carbon is the equivalent Vienna PeeDee Belemnite (VPDB) standard (Clark and Fritz 1997; Kendall and Caldwell 1998). Use of VPDB indicates the standard has been calibrated to 0‰ according to the International Atomic Energy Agency (IAEA) guidelines (Coplen 1996). Expression of isotopic composition uses differential notation, in other words, terms of ? values (parts per thousand differences from a standard):
?Xstd = [(Rsample/Rstandard) –1] x 1000,
where X is 13C, the isotope ratio reported in delta units relative to a standard; Rsample/Rstandard is the absolute isotope ratios of the sample and standard, 13C/12C (Peterson and Fry 1987; Ehleringer and Rundel 1989; Hobson et al 1994). Multiplying by 1000 (‰) expresses values as “parts per thousand” or “per mil” allowing very small differences between samples to be examined more clearly (Peterson and Fry 1987; Ehleringer and Rundel 1989).
Isotope Relationship between Host Plants, Aphids, and Carabids:
Plants convert sunlight, water, and carbon dioxide to organic materials thereby storing sunlight as usable energy within plant tissues. Plants use two distinct pathways to accomplish this energy conversion. One photosynthetic pathway used by plants (e.g. alfalfa) produces three-carbon molecules and is called the Calvin cycle (C3). Other plants (e.g. sorghum) use the alternative Hack-Slack pathway (C4) which produces four-carbon molecules. C3 and C4 plants have distinctly different carbon isotope ratios that provide a predictive relationship with ?13C values as 13C depletion continues (Bender 1968). In C3 plants, the accumulated levels of 12C are higher than 13C (–20 to –35‰) compared to atmospheric CO2 (ca. –7.7‰). C4 plants have measurably higher 13C levels (–9 to –14‰) compared to C3 plants. Alfalfa (C3) and sorghum (C4) have specific aphid species that only feed on these particular plants and should reflect the isotope ratios of their host plants.
Animal tissues that reflect a predictable carbon isotope enrichment or depletion rate when compared to dietary intake are used to reconstruct diet histories. Evidence of migration between isotopically discrete food webs can be retained in animal tissues for a period of time depending on elemental turnover rates. Stable isotopes are fractionated (enrichment or depletion) through the enzymatic transformation and assimilation of food within animal tissues. DeNiro and Epstein (1978) used mice to demonstrate that ?13C values were similar in whole-animal vs. bulk dietary intake. However, they found that ?13C values in tissues differed in a sequential pattern. Tieszen et al. (1983) verified these results using gerbils. Tieszen et al. (1983) demonstrated that by switching the diet from corn (C4) to wheat (C3) carbon replacement in gerbil tissues was dependent on tissue type (i.e. liver half-life = 6.4 days vs. muscle half-life = 27.6 days). These rates are dependent on fast or slow turnover of isotopic compositions. Carabid flight muscles and soft organs are metabolically active and can reflect recent dietary turnover of carbon isotopes in a short period of time. In contrast, carabid elytra, wings, and pronotal exoskeleton are basically metabolically inactive. Therefore, these tissues retain carbon isotope compositions from the beetles past dietary intake. These inactive components retain larval compositions indicating natal origins.
Examination of carabid movement or dispersal based on carbon isotope ratios can only be done within systems with distinct 13C sources (Prasifka and Heinz 2004). Aphids will exhibit isotopic signatures of the crop type (C3 or C4) they are consuming. Consequently, carabids will reflect the isotopic signatures of aphids preyed upon. Boutton et al (1983) demonstrated termite preferences for C3or C4 plants at two locations in the grasslands of East Africa. This work demonstrated that within colonies termites focused on one vegetation type while between locations the vegetation utilized varied. Using alfalfa (C3) and sorghum (C4) as isotopically discrete habitats, carabid dispersal patterns can be reconstructed.
1.Quantify carabid colonization of annual crops (sorghum/winter wheat) from a semi-permanent habitat (alfalfa) as it relates to disturbance (tillage);
2.Elucidate carabid dispersal powers through prey selection, diet changes within and among habitats, and larval habitat utilization;
3.Provide results of this research to producers and IPM professionals.
This study was conducted at the South Central Research Station (SCRS) in Chickasha, Oklahoma. General landscape influences consist of riparian habitat of the Washita River and the urban area of Chickasha. There were three replications labeled Plot A, B, and C. Each plot consisted of one mature alfalfa field (600 x 550 feet) and five strips of sorghum (each 50 x 150 feet) (See Figure 1). Sorghum strips were surrounded by open tracks (25 feet on each side) on the east, west and south sides. Open tracks were maintained by periodic undercutting to a depth of approximately four inches. The north end of all sorghum strips (See Figure 1) interfaced with the alfalfa allowing carabid movement between crops. Silt fencing was installed in the open tracks at a distance of 25 feet from each sorghum strip to control migration between strips. Fencing was buried six inches underground and extended 18 inches above soil line. All plots were managed under normal farming practices for Oklahoma. Crop management excluded insecticides and pasturing. Seed variety remained consistent throughout replications: alfalfa OK49, winter wheat OK101 (50 x 75 feet winter treatment in strip 3 of each plot), and sorghum SG/Garrison 82.
During the two years of sampling, sorghum summer tillage treatments were as follows: Strip 1. No-till and remained no-till throughout the study; Strip 2. Received normal tillage throughout the study; Strip 3. Received normal tillage throughout the study; Strip 4. Normal tillage to the northern half throughout the study and after the first season sorghum harvest was completed the southern half (50 x 75 feet) remained fallow for the rest of the study; Strip 5. Received normal tillage the first year and no-till in second year. Winter treatments (from October to April) used after sorghum harvest were as follows: Strip 1. No tilling will take place and sorghum residue remained; Strip 2. Soil was prepared for spring planting by tilling and over-winter without further treatment; Strip 3. The soil was prepared for planting throughout the strip but only the southern half (50 x 75 feet) was planted in winter wheat and the northern half (50 x 75 feet) remained unplanted; Strip 4. The northern half was prepared for spring planting by tilling and then left to over-winter without further treatment and the southern half remained fallow; Strip 5. Strip remained untilled and sorghum residue remained. Summer treatment in alfalfa consisted of mowing, drying, and baling off alfalfa approximately every 28 days depending on field conditions and weather. October through April, alfalfa was not mowed and left to over-winter without further treatments.
Carabid Sampling Procedures:
Standard pitfall data provides activity-density rather than absolute density for carabids. Carabid populations were sampled by standard pitfall trapping methods (Luff 1996) for a two year period in 3-5 year old alfalfa fields, annually planted sorghum, and winter wheat. Each trap was constructed from a 32 ounce plastic cup buried in soil so that the lip was at ground level, a five ounce plastic cup containing one ounce of 50% low-toxic antifreeze and 50% water was placed inside the larger cup, a plastic funnel-shaped cup with the bottom removed was placed inside the rim of the largest cup over the killing fluid (See Figure 2). Each trapping unit consisted of a metal guide (6 x 48 inches) with a trap placed at both ends. Samples from each trap within a unit were pooled in a 50 ml polypropylene tube labeled with the date and unit number. A trap unit was placed in the sorghum at five and fifteen feet from the alfalfa/sorghum interface. Units were then placed every 30 feet for the entire length of the strip (See Figure 3). Trap units were placed in the alfalfa along the west and east outer boundary along with one unit approximately 120 feet from the crop interface along the northern boundary of the alfalfa (See Figure 4). Traps were opened immediately after the sorghum was planted. Samples were collected every 24 hours for the first 15 days, every 48 hours on days 16-30, and after 30 days traps were closed for 72 hours and then opened for 96 hours and sampled. This procedure of 72 hours closed and 96 hours open trapping continued each week until sorghum harvest. Following harvest, trapping took place in all strips from October through April using one 96 hour sampling period per month. During these months, sampling time was determined by the weather conditions. Data from the first 15 days will be analyzed for colonization rates.
Once the samples were back in the laboratory they were cleaned and placed in lysis buffer for long term storage. Carabids were identified to species and a voucher collection placed in the K. C. Emerson Entomology Museum at Oklahoma State University, Stillwater, Oklahoma.
Selected Species from Previous Sampling for Further Study
Calosoma affine, Cicindela punctulata, Cratacanthus dubius, Cyclotrachelus torvus, Pasimachus elongatus, Poecilus chalcites, Scarites subterraneus, and Tetracha virginica were collected during sampling and were used for isotope investigation. All eight of these species are predators in agroecosystems of the Southern Great Plains. These carabid species represent a sub-sample of the total number of beetles trapped in each year. This was necessary due to processing cost and the amount of time required dissecting each beetle. Carabid stable carbon isotope (SCI) compositions were determined and used to elucidate movement in and among crops used in this study.
In Oklahoma, four aphid species found only in alfalfa include the spotted alfalfa aphid (Therioaphis maculate), pea aphid (Acyrthosiphon pisum), blue aphid (Acyrthosiphon kondoi), and the cowpea aphid (Aphis craccivora). Aphid sampling in alfalfa during 2006 and 2007 found that blue and pea aphids were the most abundant. The corn leaf aphid (Rhopalosiphum maidis) is found on sorghum but not on alfalfa in Oklahoma. This aphid was the only species found and collected in sorghum during 2006 and 2007. Once the aphids were identified to species they were combined by species, location, and date to provide sufficient sample material for processing.
Stable Carbon Isotope Field Sampling:
Plant samples were taken from each strip of sorghum and each alfalfa field once in the spring and fall of 2006 and 2007. Each plant collected was cut three to four inches below the soil surface to insure that roots are included in the sample. Once the plant was cut it was placed inside a zip-lock bag and labeled for transport and storage in a freezer until they were processed. Along with the plant samples, aphids were collected from each sorghum strip and alfalfa field. These aphids were removed from the plants by sweep netting and a small brush. Once the aphids were removed they were placed in labeled zip-lock bags for transport back to the laboratory where they were frozen until preparation for SCI processing.
Sample Preparation for SCI Processing:
Collected plant materials were dried in a mechanical convection oven set at 65 to 70 ?C for a minimum of 48 hours. This dry material was ground by hand in preparation for the final grinding. Next, this roughly ground sample material plus a 6mm glass bead were placed in a 2.0ml Screw Cap Microtube (Quality Scientific Plastics) and ground for 180 seconds using a Mini-Beadbeater 3110BX resulting in a fine talcum powder (1.5mg total) suitable for SCI processing. Aphids were identified to species then placed in microcentrifuge tubes to be dried in the mechanical convection oven at 40 ?C for a minimum of one week. Carabid beetles were identified to species and then each beetle was dissected into two sub-samples (Past dietary intake and Recent dietary intake). Carabid elytra, wings, and pronotal exoskeleton are basically metabolically inactive. Therefore, these tissues retain carbon isotope compositions from the beetles’ past dietary intake and were used as the P sub-sample. In contrast, carabid flight muscles and soft organs are metabolically active and can reflect recent dietary turnover of carbon isotopes in a short period of time. These tissues were used in the R sub-sample. Each sub-sample was placed in a microcentrifuge tube and dried in a mechanical convection oven at 40 ?C for a minimum of one week. All 1.5mg samples remained in the labeled microcentrifuge tubes for shipping to the University of Arkansas Stable Isotope Facility, Fayetteville, Arkansas.
The final analysis for colonization and tillage impact on carabid adults is in process for 2006 and 2007. There were a total of 2,414 beetles trapped in 2006 and 2,652 in 2007 (See Graph 1).Colonization data was collected from the first day the pitfall traps were opened and continued for 15 days in sorghum. Carabids were collected every 24 hours for this time period. A total of 8 sampling dates were completed in 2006 and 10 in 2007. Data revealed that in 2006, five carabid genera, Anisodactylus, Clivina, Cratacanthus, Harpalus, and Scarites, were trapped at the greatest distance (150 feet) from the sorghum-alfalfa interface on Day 1. The genus, Chlaenius was trapped at five feet from the interface on Day 1, then at 30 feet on Day 2, and at 150 feet on Day 3. Carabids from the genus Cicindela were trapped at 120 feet from the interface on Day 1 and 2, by Day 3 this genus had been trapped at150 feet. On Day 1 the genus Cyclotrachelus was trapped at 120 feet and at 150 feet on Day 2. These data indicate that traps placed at these distances from the crop interface can provide resolution to detect small distances covered over time. Two new genera were trapped on Day 2, Apristus at 90 feet and Stenolophus at 60 feet. Analysis for other 2006 dates is continuing. In 2007, genera Calosoma, Cicindela, Cyclotrachelus, and Scarites were trapped at 150 feet on Day 1. Cratacanthus was trapped at 30 feet on the first day and then at 150 feet on the second day. On Day 4, Poecilus was trapped at five feet and Pasimachus was trapped at 90 feet. Both of these genera were trapped at 150 feet on Day 6.
The impact of tillage was measured in two time periods during the sorghum growing season. Period 1 represents the time from planting through early crop development and initial environmental stabilization following disturbance regimes. Period 2 represents the time of crop maturation through harvest. Average number of carabids per trap in NT and CT were similar in Period 1 of trapping. During Period 2 averages for CT increased and decreased for NT (See Graph 2).
No-till habitats have a more stable initial environment, provide immediate resources, and prey despite planting activity. Over time this habitat continues to provide these conditions and resources allowing carabids to forage more efficiently thereby decreasing their activity-density. Since carabids are foraging less the likely-hood they will be trapped decreases, providing one explanation for the decrease in the average number of carabids per trap in NT over time in 2006. Additionally, NT habitats have more ground cover which is known to slow carabid foraging thereby decreasing the opportunities to be trapped. In contrast, CT environments experience catastrophic disturbance destabilizing the physical habitat and resources. These conditions take longer periods of time to recover and stabilize. Once stabilized, the resources available in CT are less numerous and highly dispersed; this increases the time carabids spend foraging. An increase in foraging activity increases the opportunities for carabids to be trapped which explains the rise in the average number of carabids per trap overtime in 2006. Another contrast to NT is the open ground between crop rows in CT which allows carabids to forage faster and farther within this habitat. ANOVA indicated no significant difference in trap catches between NT and CT in Period 1 (p = 0.053); however, there is a significant difference between NT and CT in Period 2 (p = 0.013). Analysis of 2007 tillage impact is in process.
For 2006, dispersal of 652 target carabids has been analyzed based on their stable carbon isotope ratios (SCIR, See Figure 1). Isotope data provided evidence that 394 carabids moved from alfalfa to sorghum and 57 moved from sorghum to alfalfa. This trend indicates that semi-permanent alfalfa was being used as a refuge during the early stages of soil preparation (tillage) and planting of sorghum. This SCIR data revealed that 141 carabids did not move from alfalfa and 24 carabids did not move from sorghum. These isotope results are supported by the trap data. For 57 carabids, either the P or R sample had an isotope ratio within the range of -18.50/00 to -20.5 0/00, and 12 carabids had both isotope ratios in the range of -18.50/00 to -20.5 0/00. Dispersal for these 69 carabids has not been determined.
For 2007, dispersal for 449 target carabids has been analyzed based on their SCIR at this point in time (See Figure 2, partial data set). Based on the isotope data, 237 carabids moved from alfalfa to sorghum and 4 moved from sorghum to alfalfa. This supports the 2006 trend indicating that the semi-permanent alfalfa was being used as a refuge during the early stages of soil preparation (tillage) and planting of sorghum. Early SCIR data has shown that 164 carabids stayed in alfalfa and 5 carabids stayed in sorghum. These isotope results are supported by the trap data. For 35 carabids, either the P or R sample had an isotope ratio within the range of -18.50/00 to -20.5 0/00, and four carabids had both isotope ratios in the range of -18.50/00 to -20.5 0/00. Dispersal for these 39 carabids has not been determined.
The adult carabid elytra, pronotal exoskeleton, and wings are metabolically inactive after the adult emerges from pupation. These tissues retain the carbon isotope compositions of the dietary intake during the larval stage. Preliminary analysis of the P sample SCIR data has determined 463 carabid adults had natal origins in alfalfa. There are 42 carabid adults with natal origins in sorghum. Analysis for 147 more 2006 carabids continues and 2007 carabid natal origin analysis is in process.
Diet Switching Data:
In 2006, SCIR data show diet switching in 16 beetles (See Table 1). There were more females (n = 10) that indicated switching than males (n = 6). The amount of change between the samples ranged from -3.21 to -9.170/00. This data includes four genera, Cratacanthus (n = 7), Pasimachus (n = 6), Tetracha (n = 2), and Calosoma (n = 1). Trap data indicates that seven of these carabids were trapped in alfalfa; however, only five of these seven had SCIR that showed diet switching from a sorghum habitat to alfalfa, the other two showed sorghum to mixed habitat. Though it is not possible at this time to determine how long these five beetles were in alfalfa before their “R” tissues assimilated the new isotope ratios it is clear that their change in habitat included a change in diet. Nine carabids were trapped in sorghum. Four of the nine beetles had SCIR showing sorghum to mixed habitat. The other five beetles had P samples indicating natal origins in sorghum and R samples showing they moved into alfalfa as adults.
Preliminary analysis of 2007 data has a total of 12 carabids with SCIR indicating diet switching (See Table 2). There were more males (n = 8) than females (n = 5) showing switching. The amount of change between samples ranged from -3.55 to -13.400/00. Five genera were included in this data, Scarites (n = 5), Calosoma (n = 4), Cratacanthus, Cyclotrachelus, and Pasimachus all had one beetle each. During this season, three carabids were trapped in alfalfa and had P SCIR from a mixed habitat and R SCIR from alfalfa. The other nine carabids were all trapped in sorghum. Three of these beetles had SCIR that showed a mixed habitat to alfalfa movement. Another five had SCIR that indicate natal origins in sorghum and movement into alfalfa as adults. One carabid’s SCIR showed natal origins in alfalfa with movement to a mixed habitat prior to moving into sorghum. Further 2007 data is being analyzed and will be added to this data base.
Educational & Outreach Activities
Results from this study will be communicated to producers and IPM professionals through extension fact sheets and publication in a scientific journal (e.g. Journal of Economic Entomology, Journal of Ecological Entomology). Three manuscripts are in preparation reporting the results of this study. These manuscripts will be submitted to major peer reviewed journals for publication. It is anticipated that this research project will be available as a dissertation publication after May 2011. An oral presentation (Indianapolis, Indiana) and two posters have been presented at national (Reno, Nevada) and regional (Stillwater, Oklahoma) Entomological Society of America (ESA) meetings. A new poster is in preparation to be presented at the National ESA meeting in San Diego, December 2010.
Carabids constitute a major part of the fauna (n = 5,066) and an important part of the natural enemy assemblages in agroecosystems (Fox and MacLellan 1956; Rivard 1964, 1965, 1966; Whitcomb and Bell 1964; Frank 1971; Kirk 1971; Esau and Peters 1975). Carabid mobility increases their ability to colonize annual cropping systems and find prey within crops before they reach economic thresholds. This study provides information to producers regarding carabid colonization and dispersal abilities in diverse agroecosystems. Tillage and dispersal data demonstrates that alfalfa is utilized as a refuge habitat by carabids.
Isotope results from the selected P and R sub-sample tissues have shown a high degree of resolution for determining movement and diet switching for individual beetles. These results have provided evidence that determining the differences in isotope ratios between predators, prey, and host plants within isotopically discrete agroecosystems the dispersal of carabids can be traced among habitats (Ostrom et al. 1997; Hobson et al. 1999). The stable carbon isotope ratios have revealed dietary history over time which has been used to determine carabid dispersal and diet switching (Peterson and Fry 1987; Hobson and Clark 1992).
This data supports the need for diversifying agroecosystems to provide carabids with the various habitats necessary to complete all life stages. By including cultivated and non-cultivated areas within agroecosystems it is possible to reduce mortality to carabids during cropping system disturbance regimes. Coupled with this diversification, a reduction of pesticide use within these systems will decrease environmental contamination and conserve other natural enemies from unnecessary mortality.
By using less broad-spectrum pesticides, producers can reduce unnecessary mortality to natural enemies, thereby, benefiting from the biological control services provide by these predators. Pesticides are an important tool in an IPM program; however, unnecessary preventative applications or misuse can cause a breakdown in the life cycle of natural enemies, like carabids, leading to pest resurgence episodes that require additional insecticide applications, and can cause a greater risk of insecticide resistance in pests. Using habitat management and IPM programs that support and enhance natural enemy populations, like carabids, inputs costs can be lowered.
Based on the results from this study producers have important information on natural enemy conservation that will provide a basis for habitat management decisions. By manipulating cultural farming practices, reducing the use of broad-spectrum pesticides, and diversifying agroecosystems, the economic and ecological sustainability of farms in the Southern Great Plains will be improved.
Areas needing additional study
Carabids are important predators in agricultural systems; however, there are an abundance of additional predatory species that help to suppress insect pests in crops. It is important to include these additional species in future conservations studies, particularly in no-till cropping systems. Additionally, alfalfa and sorghum are important crops in the Southern Plains, but crops such as winter wheat, cotton, canola, soybeans, and corn are planted on millions of additional acres. Further study on the interactions among insect predators, alfalfa habitats and these additional crops is also needed for whole farm pest management planning.