Final Report for GNC07-086
We compared blueberry fields with native perennial flower plantings on their perimeters to fields without flower perimeters in order to determine the impact of this conservation strategy on beneficial insects in crop fields. We found significantly more pollinators and natural enemies of crop pests in the fields adjacent to wildflower plantings. Natural enemies (mostly parasitoid wasps) were especially impacted by the presence of flowers, and were found in greater abundance in fields with flower plantings even 40 meters inside fields. Also, a late-season recovery of natural enemies following pre-harvest insecticide applications was seen only in fields adjacent to wildflower plantings.
Stands of flowering plants can provide many resources for beneficial insects, including nectar, pollen, alternate prey, and a complex architecture that provides shelter from the elements. However, many agricultural landscapes in the North Central Region lack the flowers that would have historically provided these resources, and this has compromised the ability of farmers to rely on natural enemies for pest control or on native pollinators for crop pollination. In this two-year project we tested the hypothesis that supplemental native flower strips sown in the border of blueberry fields would provide a benefit to growers by increasing local populations of beneficial insects.
There has been a growing interest in recent years about the economic and ecological benefits of re-incorporating natural habitats into agricultural systems (Bianchi et al. 2006, Kleijn and Sutherland 2003, Landis et al. 2000), in part because of the documented declines in populations of beneficial insects (e.g. Biesmeijer et al. 2006). The suspected reasons for these declines include pesticide use, loss of habitat, and a paucity of flowering plants within agricultural landscapes (Carvell et al. 2006, Landis et al. 2000).
Natural habitat outside the cropped area has consistently been shown to support beneficial insects (Bianchi et al. 2006, Kremen et al. 2002, Kremen et al. 2004, Steffan-Dewenter 2003), but this is something that most growers cannot manipulate easily. Lands adjacent to fields are often not owned by the grower, may be managed for wood production rather than to support natural enemies, and may be urbanized. Also, farms are increasingly situated adjacent to human development, and setting aside land for supporting beneficial insects is not always economically feasible. For these farms, providing resources directly into the field border is more likely to be adopted as a strategy to create habitat for beneficial insects.
Crop fields in the North Central Region used for fruit and vegetable production have strips of land around them that are typically mown. These headlands are potential areas for integration of flowering plants once the benefit of these practices is demonstrated to growers.
Manipulation of the environment around cropped areas by establishing flowering plants can increase natural enemy populations (Long et al. 1998, Rebek et al. 2005) and provide forage for wild bees that can increase their abundance (Buchi 2002, Kells et al. 2001). Provision of nectar and pollen by these plants can lead to greater parasitoid survival and fecundity (Jervis et al. 1993, Wackers 2004). This approach has also been demonstrated to reduce pest populations in Brassica (White et al. 1995) and cereal fields (Hickman and Wratten 1996), although adjacent flowering plants had no consistent effect in broccoli (Zhao et al. 1992).
Cover crops can be a useful tactic to support natural enemies in crop fields (Nicholls et al. 2000, Kinkorová and Kocourek 2000, Bugg and Waddington 1994). Unfortunately placement of the resource plants inside conventional crop fields inevitably creates potential for disturbance or death of beneficial insects when the crop is cultivated or treated with insecticide(Lee et al. 2001). Placement of these resources outside the crop area provides a more benign environment for beneficial insects where they can feed on nectar and pollen, utilize alternate hosts, and find refuge in an area not impacted by harmful disturbances (Sotherton 1984, Thomas et al. 1991).
This project is of particular relevance to specialty crop farmers that are under pressure to reduce pesticide inputs while also producing the highest quality food. These crops are becoming more important in our region as commercial farms diversify, small farms are established to supply fresh food to local markets, and the public increasingly values fresh produce grown near to the point of sale. We tested whether sown native flower strips can support beneficial insects and thereby provide greater pest control and pollination in specialty crop landscapes, with the aim of building a foundation for more effective conservation of natural enemies and pollinators in the region.
- 1. Determine the impact of a flowering perennial strip on the abundance of natural enemies and pests in the adjacent blueberry field.
2. Determine the effect of a perennial strip on abundance and diversity of native bees in the adjacent blueberry field.
3. Determine the effect of native bees on blueberry pollination.
4. Determine effect of the flower strips on the nesting activity of native cavity-nesting bees.
Nine species of native flowering perennials that rated highly for attraction of beneficial arthropods and bloom at different times of the season (Fiedler and Landis 2007b, Fiedler and Landis 2007a, Tuell et al. 2008), plus one native grass control were planted as plugs (one-year-old plants) in spring 2006. Each plot was planted with 20 plants of each species, supplied by WildType nurseries (Mason, Michigan). Each species was replicated three times within each strip in 2 x 2 m plots, in a randomized complete block design, to create a 60 x 2 m strip of flowering plants. At each of four commercial blueberry farms in Michigan’s Van Buren (2 farms) and Ottawa (2 farms) counties, two fields were selected, so that at each farm one field was adjacent to a flower strip (flower) and one was adjacent to a typical mown field border (control). The flower strips were separated from the crop by a narrow drive lane.
At all fields (n=8), unbaited yellow sticky traps (Great Lakes IPM, Vestaburg, MI) were placed along three transects into the field in four positions: field perimeter (flower strip or mown), first blueberry bush (0m), and 20m and 40m into the field. Yellow sticky traps were deployed for one week intervals from late June to mid-August in 2007. Sample dates in 2008 were selected to match the growing degree day accumulations (6 °C base) for the first 2007 sample to minimize annual variations in insect abundance due to climatic variation between years.
Natural enemies trapped on yellow sticky cards were counted in the laboratory using a magnifier lamp and/or dissecting scope as needed. Primary texts used for identification were (Borror et al. 1992, Flint and Dreistadt 1998, Marshall 2006). Identification was done to the level necessary for determination of whether a particular specimen was a natural enemy (i.e. predator or parasitoid) or a potential pest (i.e. herbivore).
Bees were counted during the two weeks of peak blueberry bloom (May 14-28, 2007, and May 16-June 4, 2008). Counts were taken on days when the temperature was over 12°C and it was not raining. The average temperature (±SE) during bee counts was 24 °C (±0.20) in 2007 and 17 °C (±0.15) in 2008. Bees were counted while standing between rows along three transects extending from the field edge to 40 meters into the field. All bees making legitimate visits to blueberry flowers were counted and identified to family or genus on the wing when possible. A legitimate visit was defined as a visit in which the bee’s head or thorax made contact with the stigma of the blueberry flower. Bees were counted for five minute intervals at each sampling position. In both years, 4 counts were taken on different days at each sampling position to give a total of 36 samples per field at a total of 8 fields. During each count the ambient temperature was recorded using a portable weather meter placed in the shade at a height of 0.5m.
The contribution of bees to blueberry yield was assessed using mesh bags to selectively exclude pollinators in flower and control fields. Bags were constructed from nylon mesh (hole size <1mm) held on to the bush with wire twist ties. Bushes used for pollinator exclusion treatments were haphazardly selected from those at each sampling position (0, 20, and 40m) along each transect so that 9 bushes per field were sampled. On each selected bush one cluster received a mesh bag and one cluster was left open to pollinators. Only clusters with no open flowers were selected, and at the time of bagging all unopened flowers were counted. At the end of the bloom period, (i.e. when all flowers had shed their corollas), all clusters were bagged and the number of immature berries in each cluster was counted to determine percent fruit set. Clusters were harvested when approximately half of the berries in the cluster had ripened. At the time of harvest, each cluster was placed in a plastic bag and transported to the laboratory for measurement of yield parameters. The total weight of all the berries and the weight of the heaviest berry in each cluster were measured on a digital balance. The number of berries in each cluster was counted and the heaviest berry was squashed to allow the number of seeds to be counted.
In an attempt to exclude commercial honeybees and measure pollination by native bees exclusively, pollination on blueberry bushes was measured at the flower and control fields in each site before the growers placed commercial honey bee hives in their fields. This was accomplished by placing 2-year-old potted ‘Bluecrop’ bushes in the greenhouse in early spring to induce premature bloom. These plants were then placed in and removed from the fields before the growers brought in commercial beehives. Potted bushes were placed in the fields along the same transects and at the same positions described above for field bushes in 2007 to provide 3 bushes per field at each of the 3 sampling distances. In 2008, pots were only placed at the 0m and 40m positions, but another transect was added, to provide 4 bushes per field at each of the 2 sampling distances. Yield parameters were measured on potted bushes using the same procedures described above for field bushes.
The drilled plank nest traps consisted of six 1 x 4 inch boards of untreated pine placed in a white box constructed of pine boards painted on the outside with white exterior latex paint. Each board had four holes drilled into it either 0.25 inch (large) or 0.18 inch (small) diameter. The holes were drilled at the surface of the wood with the tunnel exposed so that it was possible to view the nest that the insect was building in the tunnel. The tunnel was covered with a thin sheet of nitrile plastic and a piece of felt. Three boards each of the same hole size (large or small) were stacked on top of one another all held together with duct tape in a box measuring 6.5 x 4 x 6.5 inch. The large and small hole groups were randomly assigned a top or a bottom position in each nest trap.
These nest traps were placed in the fields in early May of each year and removed in late August for three consecutive years (2006 – 2008). All nest traps were located in a row parallel to the flowering plant strips, on steel fence posts, at a height of 1m, facing the adjacent blueberry field. Nesting activity was evaluated weekly by counting the number and type of finished nests visible from the front of each box. At the end of each season the contents of the nest boxes were removed and samples of developing insects were reared for identification. No nest boxes were placed in the control fields.
In 2008, to evaluate the effectiveness of the drilled plank nest traps we added an additional nest trap type. The cardboard/sumac traps were contained in a large box constructed from untreated pine boards painted with green exterior latex paint. The nest trap was designed to give four combinations of hole size and material: sumac branches with a hole diameter of 0.25 inch or 0.18 inches and hollow cardboard tubes with diameter of 0.25 inch or 0.18 inches. Cardboard tubes were interspersed among undrilled sumac branches so that hole spacing would not be confounded with substrate. Each drilled sumac branch or cardboard tube represented 1 potential nesting space. In order to create the holes in the sumac, a drill bit was used to drill one hole 6 inches into each 6.5 inch long sumac branches. The diameter of the sumac branches ranged from 0.25 inch to 1.5 inch. Most sumac used was fresh cut and alive at the time of harvest. The large and small cardboard tubes were bought from Jonesville Paper Tube Corporation (Jonesville, MI).
One cardboard/sumac nest trap was placed at each farm, in the same location as the drilled plank nest traps. Each cardboard/sumac trap contained 48 nesting sites for each hole size and material to give 192 total nesting spaces for this trap type. Nesting activity in these traps was evaluated weekly by counting the number and type of finished nests visible from the front of each box (2008 only). In July and August 2008 all nesting materials were removed from these traps and replaced with new, empty tubes and drilled branches. The collected nests were then opened and developing larvae were placed in gelatin capsules for storage, so that they could be identified and/or released in the same fields the following year.
In two years of sampling a total of 20,961 natural enemies (i.e. beneficial insects not including bees) were collected on sticky traps. Of these, the majority were parasitoid wasps (91% and 93% in 2007 and 2008, respectively). Other important groups included Orius spp. (3% of the sample in 2007 and 1% in 2008) and Syrphid flies (1% in 2007 and 2% in 2008).
Major pests of Blueberry were captured in very low numbers in all fields in both years. Japanese beetle (Coleoptera: Scarabaeidae: Popillia japonica Newman) composed less than 0.01% of the samples in both years. Cranberry fruitworm (Lepidoptera: Pyralidae: Acrobasis vaccinii Riley), was not identified to species on sticky cards, but all Lepidoptera as group made up less than 1% of the samples in both years. Blueberry maggot (Diptera: Tephritidae: Rhagoletis mendax Curran) was found in less than 0.05% of samples in both years.
The most abundant general pest groups were aphids (Hemiptera: Aphididae) and thrips (Thysanoptera: Thripidae). Thrips represented 56% (161,669 individuals) of the pest group in 2007 and 45% (31,208 individuals) in 2008, but this is likely an overestimate because no distinction was made between predatory thrips and herbivorous thrips. The aphids as a group represented 38% (108,617 individuals) of the pests sampled in 2007 and 40% (27,798 individuals) of the pests in 2008. The only other potentially pestiferous group that composed greater than 1% of the samples in either year was the leafhoppers (Hemiptera: Cicadoidea), which made up 4% and 7% of the pests in 2007 and 2008, respectively.
Analysis of insect counts was performed by repeated measures ANOVA (PROC MIXED, SAS Institute, 2001). The full model included farm as a random variable, and treatment (flower vs. control), distance, week and all possible interactions as fixed effects. Week was specified as the repeated measure effect with the transect by distance interaction as the subject (nested within farm by treatment by distance), using a compound symmetry covariance structure.
In both years, natural enemy abundance was significantly affected by week (P<0.0001), distance from the field perimeter (P<0.0001), and the week by treatment interaction (2007: P=0.0001, 2008: P=0.046). A significant treatment by distance by week interaction was detected in 2007 (P=0.037), but not in 2008 (P=0.9987). Examination of the strength of this interaction at different distances and weeks revealed significantly fewer natural enemies in the flower strips compared to control perimeters in the first two weeks of 2007 (June 15th, field perimeter: P=0.026; June 24th, field perimeter: P=0.037), but significantly more natural enemies at different distances into the fields adjacent to the flower strips during the first week and last two weeks of that year (June 15th, 40m: P=0.008 ; Aug. 10th, 20m: P= 0.009; Aug. 17th, 40m: P=0.01). The significant treatment by week interaction indicates that natural enemy abundance varied with the time of year (week) and whether or not a flowering plant strip was adjacent to a field. For example, in the early half of the season, we caught more natural enemies near flower strips on the first sample of 2008 only (July 2nd, P=0.0019). In the later samples during both seasons, we caught significantly more natural enemies in the fields adjacent to flowering plant strips (2007: Aug. 10th, P=0.02; Aug. 17th, P=0.006; 2008: Aug. 13th, P=0.039; Aug. 20th, P=0.002; Aug. 27th, P=0.001). This late-season surge in natural enemy abundance near wildflower strips suggests that the flowering strips may be acting as a source for beneficial insects following pre-harvest insecticide applications made in late July. The main effect of flower strip treatment was not significant for natural enemy abundance in either year (2007: P=0.32; 2008: P=0.13), and neither was the treatment by distance interaction. However, at all sampling distances during both years, we caught more natural enemies on traps near flower strips (2007: Flower (mean±SE) = 4.7±0.18; Control = 3.8±0.18), and this difference was greater in 2008 (2008: Flower= 4.0±0.18; Control = 2.8±0.11).Thus, there was a consistent trend towards increasing natural enemy abundance in fields adjacent to flowering plant strips. Flowering plant strips also had a significant effect on pest abundances. Pest data were analyzed using the same statistical model as natural enemies. When all pest groups were included together, there was a significant effect of week (2007: P<0.0001; 2008: P<0.0001), distance (2007: P=0.01; 2008: P<0.0001), and the week by treatment interaction (2007: P=0.006; 2008: P=<0.0001), in both years. This indicated that there were more pests later in the year and pests were more abundant closer to the field perimeters at all times of year. Closer examination of the week by treatment interaction revealed that pests were more abundant in fields adjacent to flower strips in the first three weeks of 2007 (June 16th, June 24th, July 5th, P<0.05). In 2008, there were significantly more pests in fields adjacent to flower strips in 4 out of 6 samples (July 2nd, July 9th, July 16th, Aug. 13th, P<0.05), and the remaining two samples had marginally significant differences (Aug. 20th, P=0.051, Aug. 27th, P=0.067). The main effect of treatment was only significant for pest abundance in 2008 (2007: P=0.078; 2008: P=0.041) meaning that there were significantly more pests in fields near flower borders in that year. Analysis of the abundance patterns of each pest group individually could only be performed on the most abundant groups, i.e. aphids and thrips, because data from other groups did not meet the normality assumptions of the model. This analysis revealed that the pattern in overall pest abundance described above was primarily driven by thrips abundance. Thrips were significantly more abundant later in the season (week effect P<0.0001), especially in fields adjacent to the flower strips (week by treatment interaction (2007: P=0.03, 2008: P<0.0001). Thrips were more abundant in fields adjacent to flower strips compared to controls in 5 of 6 samples in 2007 (P<0.05) and all 6 samples in 2008 (P<0.05). However, the distance by treatment effect was not significant for thrips abundance in either year (2007: P=0.67, 2008: P=0.23), nor was the main effect of distance significant (P>0.05), which means that thrips abundance was evenly distributed across all distances within fields in both years.
Aphid abundance was significantly affected by time of year (week effect, 2007: <0.0001, 2008: P<0.0001) and distance (2007: P<0.0001, 2008: P=0.0002), but not by the distance by treatment interaction (P>0.05) or the week by treatment interaction (P>0.05). Thus, aphids were more abundant in the field perimeters compared to sampling distances inside the fields (P<0.05) in both years, but not more abundant in fields adjacent to flower strips compared to controls in either year (treatment effect, 2007: P=0.27, 2008: P=0.22). To summarize these results: the pattern in overall pest abundance described above was driven by contrasting responses of the two most abundant pest groups (thrips and aphids). Thrips were generally more abundant in the fields adjacent to flowering plant strips, but evenly distributed with respect to distance. In contrast, aphids were not more abundant in fields adjacent to flowering plant strips, but had a higher abundance in the field perimeters of both treatment types. Natural enemies, composed primarily of parasitoid wasps, were consistently more abundant in fields with flowering plant strips compared to controls, especially later in the season.
We counted native bees pollinating blueberry flowers during peak bloom in 2007 and 2008. Native bees observed pollinating blueberry flowers were primarily soil-nesting bees (Andrenidae, Halictidae), although bumble bees (Bombus spp.) and cavity-nesting bees (Megachilidae) were also observed. Unfortunately, diversity analysis could not be performed because of the extreme rarity of native bees in our samples (0.26 native bees (+/- 0.02) per 5 min. sample in 576 samples). In 2007, there were an average (+/- Standard Error) of 0.39 (+/- 0.06) and 0.22 (+/- 0.04) native bees per 5 min. sample in flower and control fields, respectively. In 2008, there were an average (+/- SE) of 0.26 (+/- 0.05) and 0.15(+/- 0.04) native bees per 5 min. sample in flower and control fields, respectively. Native bee abundance was too low for traditional analysis of variance (ANOVA), but a non-parametric analysis (Wilcoxon Rank-Sum, PROC NPAR1WAY, SAS v.9.1) revealed that the higher native bee abundance in fields with flowering plant strips during both years was statistically significant (P<0.05).
Average berry weight from the potted blueberry plants was statistically indistinguishable between the flower and control fields in both years. In 2007, average berry weight was 0.65 g (+/- 0.08) in fields with flower strips and 0.65 g (+/- 0.07) in control fields. In 2008, average berry weight was 0.49 g (+/- 0.05) in fields with flower strips and 0.48 g (+/- 0.06) in control fields. Proportion fruit set was also essentially the same between the two types of fields in both years. In 2007, average proportion fruit set was 0.29 (+/- 0.05) in fields with flower strips and 0.34 (+/- 0.08) in control fields. In 2008, average proportion fruit set was 0.41 (+/- 0.04) in fields with flower strips and 0.40 (+/- 0.05) in control fields.
In order to measure the contribution of wild bees to blueberry yield we placed mesh bags over flower clusters on these potted plants and compared the average berry weight on bagged clusters to clusters that had been left open to pollinators. In 2007, the average difference in berry weight between bagged and open clusters was 0.26 g (+/- 0.08), and in 2008 the average difference was 0.11 g (+/- 0.05). In other words, between 40% and 22% of the weight of the average berry in 2007 and 2008 can be attributed to the effect of wild pollinators in the absence of commercial honey bee hives.
In the first two years (2006-2007) only cavity nesting wasps (Eumenus spp. and Isodontia spp.) and one type of leaf cutter bee (Megachile sp.) were found nesting in the drilled plank nest traps. However, in 2008, for the first time, we found several individuals of Megachile pugnata Say nesting in the drilled plank nest traps. This suggests that native bee populations in 2008 were benefiting from the pollen resources provided by the flowering plant strips, which (planted in 2006) provided their first full season of bloom in 2007.
Counts of the numbers of nests built in the drilled plank traps over three years, showed a consistent positive trend in the nesting activity of cavity-nesting insects from 2006 to 2008. At the end of the 2006 season a total of 75 nests had been built in traps at all four farms. At the end of the 2007 season a total of 128 nests had been built, and by the end of the season in 2008, a total of 214 nests had been built at all four farms. In 2006, The majority of these nests were built by mason wasps (Eumenus spp.) and grass-carrying wasps (Isodontia spp.) (N. Walton, personal observation). In 2007, 3 nest types were identified: mud (Eumenus spp.), grass (Isodontia spp.) and leaf (Megachile spp.). As a percentage of all nests built during that year, 92% (mean±SE total nests averaged across samples = 94.2 ± 4.1), were built by wasps and 8% were built by bees (8.7±1.2). In 2008, 5 nest types were identified: mud (Eumenus spp.), grass (Isodontia spp.), leaf (Megachile spp.), masticated leaf (Megachile pugnata Say), and resin (Crabronid wasps). Of these, 93.4% (145.4±18.5) were built by wasps and 6.6% (10.3±1.4) were built by bees. This translates into a 54.4% increase in wasp nests and an 18.8% increase in bee nests from 2007 to 2008.
Clearly these insects benefited from the floral resources and nesting habitat that were provided for them in our study fields. Grass-carrying wasps (Isodontia spp.) provision their nests with tree crickets (Orthoptera: Gryllidae), which are not likely to be serious pests in blueberry. Mason wasps (Eumenus spp.) on the other hand provision their nests with larval Lepidoptera, so they may have potential for management as a biocontrol agent. Leafcutter bees (Megachile spp.) are important pollinators of alfalfa (Delaplane and Mayer 2000), and other crops (Tepedino and Frohlich 1982), but are not present early in the season when blueberry is in bloom.
A comparison of the two different nest trap types in 2008, showed that bees were more likely to nest in the cardboard/sumac nest trap, than the drilled plank traps (P<0.0001). Within the cardboard/sumac traps bees showed no preference for sumac branches over cardboard tubes (P=0.938). Growers interested in encouraging bees on their farms should consider using cardboard tubes or a similar nesting material (e.g. hollow reeds), as it is less labor-intensive than drilled sumac or wooden planks.
Bianchi, F. J. J. A., C. J. H. Booij, and T. Tscharntke. 2006. Sustainable pest regulation in agricultural landscapes: a review on landscape composition, biodiversity and natural pest control. Proceedings of the Royal Society B-Biological Sciences 273:1715-1727.
Biesmeijer, J. C., S. P. M. Roberts, M. Reemer, R. Ohlemüller, M. Edwards, T. Peeters, A. P. Schaffers, S. G. Potts, R. Kleukers, C. D. Thomas, J. Settele, and W. E. Kunin. 2006. Parallel declines in pollinators and insect-pollinated plants in Britain and the Netherlands. Science 313:351-354.
Borror, D. J., C. A. Triplehorn, and N. F. Johnson. 1992. An introduction to the study of insects, 6 ed. Harcourt Brace, New York.
Buchi, R. 2002. Mortality of pollen beetle (Meligethes spp.) larvae due to predators and parasitoids in rape fields and the effect of conservation strips. Agriculture Ecosystems & Environment 90:255-263.
Bugg, R. L. and C. Waddington. 1994. Using cover crops to manage arthropod pests of orchards: A review. Agriculture, Ecosystems & Environment 50:11-28.
Carvell, C., W. R. Meek, R. F. Pywell, D. Goulson, and M. Nowakowski. 2006. Comparing the efficacy of agri-environment schemes to enhance bumble bee abundance and diversity on arable field margins. Journal of Applied Ecology.
Delaplane, K. S. and D. F. Mayer. 2000. Crop pollination by bees. CABI Publishing, New York.
Fiedler, A. K. and D. A. Landis. 2007a. Attractiveness of Michigan native plants to arthropod natural enemies and herbivores. Environmental Entomology 36:751-765.
Fiedler, A. K. and D. A. Landis. 2007b. Plant characteristics associated with natural enemy abundance at Michigan native plants. Environmental Entomology 36:878-886.
Flint, M. L. and S. H. Dreistadt. 1998. Natural enemies handbook: The illustrated guide to biological pest control. University of California Press, Berkeley.
Hickman, J. M. and S. D. Wratten. 1996. Use of Phacelia tanacetifolia strips to enhance biological control of aphids by hoverfly larvae in cereal fields. Journal of Economic Entomology 89:832-840.
Jervis, M. A., N. A. C. Kidd, M. G. Fitton, T. Huddleston, and A. Dawah. 1993. Flower-visiting by hymenopteran parasitoids. Journal of Natural History 27:67-105.
Kells, A. R., J. M. Holland, and D. Goulson. 2001. The value of uncropped field margins for foraging bumblebees. Journal of Insect Conservation 5:283-291.
Kinkorová, J. and F. Kocourek. 2000. The effect of integrated pest management practices in an apple orchard on Heteroptera community structure and population dynamics. Journal of Applied Entomology 124:381-385.
Kleijn, D. and W. J. Sutherland. 2003. How effective are European agri-environment schemes in conserving and promoting biodiversity? Journal of Applied Ecology 40:947-969.
Kremen, C., N. M. Williams, R. L. Bugg, J. P. Fay, and R. W. Thorp. 2004. The area requirements of an ecosystem service: crop pollination by native bee communities in California. Ecology Letters 7:1109-1119.
Kremen, C., N. M. Williams, and R. W. Thorp. 2002. Crop pollination from native bees at risk from agricultural intensification. Proceedings of the National Academy of Sciences of the United States of America 99:16812-16816.
Landis, D. A., S. D. Wratten, and G. M. Gurr. 2000. Habitat management to conserve natural enemies of arthropod pests in agriculture. Annu. Rev. Entomol. 45:175-201.
Lee, J. C., F. B. Menalled, and D. A. Landis. 2001. Refuge habitats modify impact of insecticide disturbance on carabid beetle communities. Journal of Applied Ecology 38:472-483.
Long, R. F., A. Corbett, C. Lamb, C. Reberg-Horton, J. Chandler, and M. Stimmann. 1998. Beneficial insects move from flowering plants to nearby crops. California Agriculture 52:23-26.
Marshall, S. A. 2006. Insects: Their natural history and diversity: with a photographic guide to insects of eastern North America. Firefly Books Inc., Buffalo.
Nicholls, C. I., M. P. Parrella, and M. A. Altieri. 2000. Reducing the abundance of leafhoppers and thrips in a northern California organic vineyard through maintenance of full season floral diversity with summer cover crops. Agricultural & Forest Entomology 2:107-113.
Rebek, E. J., C. S. Sadof, and L. M. Hanks. 2005. Manipulating the abundance of natural enemies in ornamental landscapes with floral resource plants. Biological Control 33:203-216.
Sotherton, N. W. 1984. The distribution and abundance of predatory arthropods overwintering in farmland. Annals of Applied Biology 105:423-429.
Steffan-Dewenter, I. 2003. Importance of habitat area and landscape context for species richness of bees and wasps in fragmented orchard meadows. Conservation Biology 17:1036-1044.
Tepedino, V. J. and D. R. Frohlich. 1982. Mortality Factors, Pollen Utilization, and Sex Ratio in Megachile pugnata Say (Hymenoptera: Megachilidae), a Candidate for Commercial Sunflower Pollination. Journal of the New York Entomological Society 90:269-274.
Thomas, M. B., S. D. Wratten, and N. W. Sotherton. 1991. Creation of 'Island' Habitats in Farmland to Manipulate Populations of Beneficial Arthropods: Predator Densities and Emigration. The Journal of Applied Ecology 28:906-917.
Tuell, J. K., A. K. Fiedler, D. Landis, and R. Isaacs. 2008. Visitation by wild and managed bees (Hymenoptera: Apoidea) to eastern U.S. native plants for use in conservation programs. Environmental Entomology 37:707-718.
Wackers, F. L. 2004. Assessing the suitability of flowering herbs as parasitoid food sources: flower attractiveness and nectar accessibility. Biological Control 29:307-314.
White, A. J., S. D. Wratten, N. A. Berry, and U. Weigmann. 1995. Habitat manipulation to enhance biological control of Brassica pests by hover flies (Diptera: Syrphidae). Journal of Economic Entomology 88:1171-1176.
Educational & Outreach Activities
The information gathered during this multi-year study has been presented to growers in the North central region through a variety of outlets. Mr. Walton presented talks about farm management to enhance pollination at two workshops, one entitled, “IPM and Nutrient Management Planning: Addressing Farm Production and Resource Conservation”, and the other, "Increasing Your Yields by Managing Your pollination." Also, the results from objective 4 were presented in a poster display at the 2008 Great Lakes Fruit, Vegetable and Farm Market Expo in Grand Rapids, MI. A similar poster entitled, “Conservation strips of native perennials to enhance beneficial insect abundance in commercial blueberry fields,” was presented at the 2008 Entomological Society of America annual meeting in Reno, NV.
We then held a meeting at one of our field sites September of 2008, attended by about 20 growers, where growers were able to see a flower planting in bloom, and hear presentations by representatives of USDA-NRCS, the Xerces society, Dr. Isaacs, and Mr. Walton, covering topics such as native pollinator conservation and how growers can receive incentives from NRCS to plant wildlife habitat on their farms.
Manuscripts are being written for publication based on the results from Objectives 1 and 4. Elements of all 4 objectives will be a part of Mr. Walton’s Master’s thesis entitled: Habitat management using native plants to increase populations of beneficial arthropods in agricultural fields, which will be completed this Spring (2009).
Native perennial wildflower conservation plantings, such as those evaluated by this research, have tremendous potential for benefiting society, the environment, and agricultural sustainability. For the grower, they can reduce erosion, encourage beneficial insects, and improve the aesthetic value of their land. For the environment, they can reduce pesticide and nutrient runoff, provide wildlife refuge, and reduce the impact of pesticide drift. All of the above in turn benefit society by improving human welfare and ensuring a sustainable food supply. We expect that as more research and education is devoted to this and similar practices more farms will incorporate them into their management strategy.
Estimates based on current costs of native seed mixes range from $700 - $3000 per acre, depending on the species composition of the seed mix. The flowering plant strips evaluated in this study were approximately 1/33 of an acre and the impact was measured at the scale of a 1 acre field of blueberry. In other words to receive the a benefit equivalent to that documented by our research a grower would need to spend between 21 and 90 dollars per acre for seed. This does not include the cost of planting, herbicide, soil preparation, etc. However, this is a one time cost if perennials are used and can be expected to provide a benefit for several years at no additional cost.
In a survey of Michigan blueberry growers in March of 2009, 17% responded yes to the question, “Do you currently have a region of your farm dedicated to beneficial insect conservation?, ” 8% said that they were planning to do so, and 59% said no and that they had never considered doing so. In the same survey, 17% of the growers said that they were receiving funds from the Natural Resources Conservation Service (NRCS) or the Farm Services Agency (FSA), but in a follow-up question only 1 of those growers surveyed was receiving those funds specifically for beneficial insect conservation.
A new FSA program introduced in January of 2008 State Acres for Wildlife Enhancement (CRP-SAFE) provides cost-sharing, rental payments, and implementation incentives to landowners who undertake practices to restore habitats that benefit high priority species conservation. In Michigan, FSA has set a goal for SAFE of preserving 2,500 acres for pollinator conservation in 22 counties in the Western Lower Peninsula. This SARE funded research will help FSA meet this goal as more growers are made aware of the benefits of integrating flowering plants into their croplands.
Areas needing additional study
This research has shown a clear increase in the populations of beneficial insects in fields adjacent to flower plantings, however it does not quantify in specific terms the benefit that this will bring to farmers who implement such practices. Studies that measure this benefit in terms of pests controlled or increases in pounds produced would provide much needed data for farmers considering uptake of habitat conservation.
We identified at least four species of cavity-nesting insects of potential economic importance for agriculture in the Northcentral region. The cavity-nesting bees (Megachile spp.) have potential for management in a pollination program if more research is done to develop a rearing and management protocol. Also, the cavity-nesting Crabronid wasp found nesting in our traps, provisioned its nests with aphids, so has potential for a management program aimed at biocontrol of these pests pending further research. Similarly, another predatory wasp found in our traps that preys on small caterpillars (Eumenes spp.) could have potential as a biocontrol agent if its prey is determined to be agricultural pests.