2nd Place: Pesticide-induced reduction of natural enemies leads to outbreak of soybean looper, Chrysodeixis includens (Walker), in Louisiana soybean, Glycine max (L.)

Soybean looper, Chrysodeixis includens (Walker), is the most abundantly collected lepidopteran defoliator in Louisiana soybean, Glycine max (L.).  Populations of C. includens frequently occur alongside other arthropod pests, like stink bugs (Family: Pentatomidae), and concurrently the insecticides used for stink bug control. Increased insecticide tolerance in certain stink bugs species has led to more frequent applications and, in turn, increased documented cases of C. includens outbreak. A reduction in natural enemies is thought to be the mechanism behind this population increase, but has yet to be delineated. To assess the cause of C. includens outbreak, a two year study (2018-2019) was conducted to monitor the effects of stink bug-related controls on C. includens and the residing natural enemy community in Louisiana soybean.  Commonly applied stink bug insecticides (acephate, bifenthrin, and clothianidin) were evaluated alongside an untreated check. Foliar-residing arthropods were monitored at 2-, 7-, 14-, and 21-days after insecticide application. Additionally, collected predators were categorized into feeding guilds (e.g. piercing-sucking, chewing, etc.). Populations of C. includens in soybean were found to be higher than the untreated check when treated with clothianidin and bifenthrin at 14- and 21-days after treatment, respectively. Also, a reduction in the predator complex, specifically the piercing-sucking feeding guild, was observed at 2-, 7-days for acephate and bifenthrin treatments, and 14-days for all evaluated insecticides. The information provided about the usage of stink bug-related insecticides and their non-target effects will allow for the development of more sustainable practices for C. includens management in Louisiana soybean agroecosystems.