Seasonal Abundance of Ground Beetles in Highbush Blueberry (Vaccinium corymbosum) Fields and Response to a Reduced-Risk Insecticide Program

Abstract

Seasonal patterns of ground beetle activity were examined at six highbush blueberry (Vaccinium corymbosum L.) farms in southwestern Michigan. On each farm, pitfall traps were used to monitor ground beetle activity in two adjacent Þelds: one managed under a conventional insecticide program (grower standard) and the other with reduced-risk insecticides. Overall, more active in- gredient was applied in grower standard than reduced-risk Þelds, with the greatest amount used in June and July. During the 6-mo sampling period, we collected 11,322 ground beetles comprised of 34 species, with Harpalus pensylvanicus DeGeer representing 70.7% of the total beetles collected. The greatest amount of ground beetle activity occurred in August and September, mostly because of increased captures of the autumn breeding species H. pensylvanicus and H. erraticus Say. Only H. erraticus responded to the different insecticide programs, with eight-fold greater captures in reduced-risk compared with grower standard Þelds. Because H. erraticus are in the soil as larvae or pupae during June and July, we suggest that greater insecticide use in the grower standard Þelds resulted in increased mortality of immature H. erraticus. At one farm, where ground cover was absent between blueberry rows,H. erraticus activity did not respond to the difference in insecticide program. This suggests that enhancement of ground beetle activity may require suitable habitat in addition to a reduction in broad-spectrum insecticide use. HIGHBUSH BLUEBERRIES, Vaccinium corymbosum L., are the most signiÞcant small fruit crop grown in Michi- gan, producing32 million kilograms of fruit annually on 7,300 ha. Harvested fruit is primarily for the pro- cessing market, although 25% of the fruit is sold fresh. The key insect pests include cranberry fruit- worm (Acrobasis vaccinii Riley), blueberry maggot (Rhagoletismendax Curran), and Japanese beetle (Po- pillia japonica Newman). The zero tolerance for fruit contamination with insects forces many growers to make multiple foliar applications of organophosphate and carbamate insecticides before harvest. Because these pests spend part of their life overwintering on the soil surface (A. vaccinii) or in the soil (R. mendax and P. japonica), predation by ground beetles (Co- leoptera: Carabidae) may be an important source of biological control of these pests. Ground beetles are generalist arthropod predators that are natural enemies of several insect pests (Sunder- land 2002). Increasing ground beetle activity under blue- berry bushes has been shown to result in greater removal