Modular habitat refugia enhance generalist predators and lower plant damage in soybeans

Promoting generalist predators in agriculture via habitat manipulation has gained much interest in biocontrol research. Straw shelters have been used by Chinese farmers for >2,000 yr to provide temporary spider refugia during cyclic farming disturbances. This method, however, has not been systematically investigated on larger scales in western-style agriculture. Our preliminary observations indicated a significant decrease in the abundance of spiders (76%) and their egg sacs (75%), after conventional tillage of soybeans [Glycine max (L.) Merr.]. We hypothesized that providing alternative habitats in tilled fields could conserve predatory assemblages following this major disturbance. We used modular habitat refugia constructed of chicken wire loosely filled with bedding straw to provide temporary habitats for epigeic predators in a soybean field. Refugia held 5-36 times the spider density compared with open field, and the production of spider egg sacs was enhanced 18-87 times. Almost 60% more spider species were found in refugia than in open field. Abundance of harvestmen, carabids, and staphylinid beetles also significantly increased in habitat refugia. Increased habitat cover and provision of alternative prey in habitat refugia may have caused this dramatic predator increase. Soybean seedlings grown within 1 m of habitat refugia suffered 33% less insect damage compared with giants at control locations. Decrease in seedling damage, however, did not significantly increase soybean seed production. Applications of discrete habitat refugia may provide an alternative to habitat manipulation techniques to conserve and augment arthropod predators in agroecosystems.