Sublethal effects of Bacillus thuringiensis biopesticides and insecticides combinations on Chrysodeixis includens larvae: insights on pest management

Abstract Ecofriendly Bt biopesticides can be used in combinations with insecticides to optimize agricultural operations and increase the host spectrum. However, this procedure can reduce the efficacy of the product and affect the biology of survival larvae. We evaluated the sublethal effects (survival, larval stage duration, weight and pupae formation) of two Bt biopesticides and eight insecticides on Chrysodeixis includens , using combinations of one Bt biopesticide with one or two insecticides, comprising 72 treatments. After the in vitro combinations assays, every susceptibility treatment consisted of 100-second instar C. includens larvae, distributed into 20 repetitions. No survival was recorded in 31 treatments, and those survival larvae from 41 treatments (1,805) were weighed every two days, from nine to 31 days after treatment (DAT). The larvae pupated (687, 38%) in only 26 treatments, and six treatments provided larval survival rates greater than 80% with Thuricide WP ® , Larvin WG 800 ® , and Premio SC ® . The weight of the surviving larvae varied both up and down in some treatments compared to the control in the first evaluation. Furthermore, most heavier larvae were pupated before the control, but the heaviest ones, most of them with longer larval stage, died before pupating. Indeed, we reinforce the importance of sublethal effects in the conception of C. includens susceptibility and interactions with ecosystems services.