Banking on Beetles for Biological Pest Management in Western Oregon Michael Russell, Biodiversity Research Collective; Gwendolyn

Ellen, Integrated Plant Protection Center, Oregon State University;

John Lambrinos, Department of Horticulture, OSU Introduction

Predacious ground beetles are known to feed on crop pests and contribute to lower pest abundances (Kromp 1999, Sunderland 1999 and Symondson, et al. 2002). Field and gut studies have shown that predacious ground beetles readily prey upon many crop pests (Kromp 1999).They play an important role in limiting outbreaks by concentrating their feeding activities to areas of high pest abundance (Winder, et al. 2005, Bell, et al. 2010). The activity of predatory beetles and spiders within crop fields tends to be influenced by field margins and grassy borders (Thomas, et al. 1991, Thomas, et al. 2001, Holland, et al. 2005, Drapella, et al. 2011). This association can be explained by the requirement of shelter for over wintering arthropods in the life histories of the species. Agricultural production practices tend to diminish the availability of over wintering refuges for beetles, and consequently a num-ber of conservation biological control strategies focus on increasing the abundance and quality of over wintering habitat in agricultural landscapes (Landis et al. 2000). One of these strategies is the creation of grassy, 1 - 2 m wide “beetle banks” that run across annual crop fields. Research in the United Kingdom has demonstrated that ground beetles seek out and benefit from the microclimate afforded by grasses on the beetle banks (Dennis, et al. 1994, Thomas, et al. 1991, Collins, et al. 2003). There has been little work on the role beetle banks and ground beetles play in Pacific Northwest agroecosystems. This poster describes a number of studies designed to describe how conservation biological control strategies focused on ground beetles and similar beneficial preda-tors can influence pest management on farms in the Willamette valley of Western Oregon.

Study sites The commercial farm study sites included three organic and hand harvested commercial vegetable farms and one larger conventional farm that grew machine harvested sweet corn and green beans. The experimental beetle banks were on a research farm focused on grain breeding. Farm habitats include vegetable, fruit, and seed production fields separated by grass roads and surrounded by forests, meadows, and blackberry thickets in areas where site con-ditions have prevented cultivation.

Works Cited

Bell, J. R., R. A. King, D. A. Bohan, and W. O. Symondson 2010. Spatial cooccurrence networks predict the feeding histories of polyphagous arthropod predators at field scales. Ecography 33 (1) : 64 - 72.

Collins, K.L., N.D. Boatman, A. Wilcox, and J.M. Holland 2003. Effects of different grass treatments used to create overwintering habitat for predatory arthropods on arable farmland. Agriculture, Ecosys-

tems and Environment 96: 59-67.

Dennis, P., M. B. Thomas, and N. W. Sotherton 1994. Structural features of field boundaries which influence overwintering densities of beneficial arthropod predators. Journal of Applied Ecology 31 : 361 –

370.

Drapella, T., T. Frank, X. Heer, D. Moser, and J. G. Zaller 2011. Landscape structure affects activity density, body size and fecundity of Pardosa wolf spiders (Araneae: Lycosidae) in winter oilseed rape.

European Journal of Entomology 108 : 609 – 614.

Holland, J. M., C. F. G. Thomas, T. Birkett, S. Southway, and H. Oaten. 2005. Farm-scale spatiotemporal dynamics of predatory beetles in arable crops. Journal of Applied Ecology 42 : 1140 – 1152.

Kromp, B. 1999. Carabid beetles in sustainable agriculture: a review on pest control efficacy, cultivation impacts, and enhancements. Agriculture, Ecosystems, and Environment 74:187-228

Landis, D. A., S. D. Wratten, and G. M. Gurr 2000. Habitat management to conserve natural enemies of arthropod pests in agriculture. Annual Review of Entomology 45 (1) : 175 - 201.

Sunderland, K. (1999). Mechanisms underlying the effects of spiders on pest populations. Journal of Arachnology 27 (1): 308 – 316

Symondson, W. O. C., K. D. Sunderland, and M. H. Greenstone 2002. Can generalist predators be effective biological control agents? Annual Review of Entomology. 47:561-494

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. Journal of Applied

Ecology 28 (3) 906 – 917.

Image 1. A beetle bank on one of the or-ganic farms in this study. Notice the differ-ence in vegetation structure between the grassy beetle bank and the cultivated fields on either side.

Study 1 Question: Which habitats support the highest numbers of beneficial predators?

Methods: Soil cores were taken in representative patches of each of the major habitat types on the four commercial farms. Soil invertebrates were extracted from the soil cores with Berlese funnels and predatory arthro-pods were identified and tallied. ANOVA was used to test for differences in arthropod numbers between habitats.

Results: Beetle banks harbored higher numbers of over wintering ground beetles than any other habitat type (P(F)11/158 = 0.001). Habitats dominated by perennial herbaceous vegetation contained more ground beetles than

habitats dominated by annuals or woody plants (P(F)2/167 = 10 -5

).

Study 2 Question: Which plant species support the highest number of beneficial predators on ex-perimental beetle banks?

Methods: A number of different native plant species were planted to sections of several beetle banks on the research farm. Arthropod sampling was the same as for Study 1 (Soil cores and Berlese extraction). Anova was used to test for differences in ar-thropod numbers between plant species and plant functional groups.

Results: Both Perennial grasses and perennial forbs harbored higher numbers of overwintering ground beetles than beetle bank sections dominated by annual forbs (P(F)2/103 = 0.05) Differences in beetle populations between plant species were not significant (P(F)13/92 = 0.07).

Study 3 What are the life histories of ground beetles that are common on western Oregon farms?

Methods: Pitfall traps were deployed across fields on the four commercial farms and after two nights the ground bee-tles in each trap were identified and tallied. Trap counts were averaged for each month over the four years of sampling to compare adult activity pat-terns. When recently emerged “teneral” beetles were observed, the timing was noted. Beetles from the feeding trial were dissected to determine breeding state.

Results: Separating ground beetles into size based groups also separates most species by their life history timing. For most mid-sized ground beetles, adults are active and breeding in the spring and early summer, larvae are active over the summer, and newly emerged adults hibernate in beetle banks over the winter. For most large ground beetles, adults are active in the late summer and early fall, larva are active over the winter and into the early summer.

Study 4 Question: How does the feeding activity of each beetle species change over their activity season? Methods: During each sampling month up to 15 individuals of each of the common ground beetle species were brought back to the lab for feeding trials. Beetles were placed in sets of five individuals into sand filled enclosures with 100 freeze killed fly pupae pasted to 5 cards. After 48 hours, the number of pupae remaining were tallied to calculate a per capita feeding rate. The number of pupae consumed per beetle in each month was compared to the monthly activity for each species. Linear regression was used to test for a correlation between relativized per capita consumption and relativ-ized activity density for all the beetles

Results: For most ground beetle species the per capita prey consumption rate rises and falls with their activity den-

sities in the field (P(F)1/67 = 0.0003)

Typical mid-sized beetles

Atypical mid-sized beetle Atypical large beetle

Typical large beetles

Study 5 Question: Is there a relationship between the activity of groups of beetles and relative risk to a potential prey item in the field?

Methods: 20 freeze filled fly pupae were pasted to cards and placed adjacent to each pitfall trap deployed on the four commercial farms. The number of fly pupae removed from each card was tallied. Results were not obtainable from a number of cards that were destroyed by slugs. Analysis was performed on seasonal means for each trap site to mitigate for the lost data. Multiple regression was used to test for a the effect of small, midsized and large ground beetle activity densities on the sentinel prey removal rate

Results: During the early and late seasons, there was a relationship between the sentinel prey removal rate and the activity density of the size-based ground beetle group that was in its main activity season, but not with the other size-based groups. During the early season (March – June) the sentinel prey removal rate was significantly higher at trap sites with more mid-sized beetles (P(F)1/431 = 0.002). During the late season (July – October) the sentinel prey removal rate was significantly higher at

trap sites with more large beetles (P(F)1/681 < 10-6

)

Implications for conservation biological control Beetle banks and other grassy perennial habitats provide important habitat for populations of over-wintering ground beetles. Over-wintering beetles are dominated by the mid-sized, early season bee-tles. One example of how this can influence pest management involves the Cabbage looper (Trichoplusia ni Hübner). Cabbage looper 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 with larvae present on the plants in June and August. The August cater-pillars are at risk from the large, late summer active beetles group, particularly P. melanarius, which is typically abundant on all farms. The June generation of looper larvae would be at risk from a di-verse group of mid-sized beetles, but those species are not always present in high numbers. On farms with lower relative numbers of spring active beetles (farm P), the associated risk for predation on the June caterpillar generation is low relative to farms with large numbers of spring active beetles (Farm H). Enhancing the populations of the spring active beetle species through conservation biolog-ical control practices like creating beetle banks is one strategy to increase the mortality of the June generation of cabbage loopers and decrease the potential for crop damage from the pest.

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Anisodactylus binotatus group Anisodactylus sanctaecrucisAgonum muelleri Agonum subserecium Amara littoralis Amara californica Harpalus affinis Harpalus pensylvanicus Metrius contractus Nebria brevicaulis Omus audouini Omus dejeaniiPterostichus algidus Pterostichus melanarius Scaphinotus marginatus BlethesiaSmall carabids Other medium sized carbidsOther large carabids Cabbage looper

Image 2. Sections of an experimental beetle bank showing areas dominated by grass and forb species.

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Anisodactylus binotatus group Anisodactylus sanctaecrucisAgonum muelleri Agonum subserecium Amara littoralis Amara californica Harpalus affinis Harpalus pensylvanicus Metrius contractus Nebria brevicaulis Omus audouini Omus dejeaniiPterostichus algidus Pterostichus melanarius Scaphinotus marginatus BlethesiaSmall carabids Other medium sized carbidsOther large carabids Cabbage looper