Immune response and susceptibility to Cotesia flavipes parasitizing Diatraea saccharalis larvae exposed to and surviving an LC25 dosage of Bacillus thuringiensis

Abstract

Biological control using entomopathogens and natural enemies is an ecofriendly method for pest management in agriculture. Biological control agents often can be simultaneously employed and compatibility between agents may improve pest suppression. We investigated the influence of the entomopathogen Bacillus thuringiensis (Bt) on the immune system of the sugarcane borer Diatraea saccharalis (Fabricius, 1794) (Lepidoptera: Crambidae) to determine if such changes impact parasitization by Cotesia flavipes Cameron, 1891 (Hymenoptera: Braconidae). The immune response of surviving D. saccharalis larvae fed with an LC25 dosage of a Bt-based biopesticide (Dipel®) was analyzed (total hemocyte count, hemocyte adhesion, and activities of phenoloxidase and lysozyme). Furthermore, the suitability of surviving Bt-fed larvae as hosts for C. flavipes was assessed by measuring parasitoid attributes such as number and size of teratocytes, weight of pupae, length of adult female tibia and number of emerged adults. Total hemocyte count, but not hemocyte adhesion, total protein content and phenoloxidase activity increased in the hemolymph of non-parasitized Bt-fed larvae (Bt-NP) compared to control larvae (NBt-NP). Lysozyme activity increased only after parasitization without Bt exposure (NBt-P). After parasitization, the immunological parameters activated in Bt-NP larvae decreased to levels at or below those observed in control larvae, showing that C. flavipes can regulate the activated immune response of Bt-fed larvae. The development of C. flavipes was not impaired in Bt-fed larval hosts (Bt-P); no changes were observed for teratocyte size, weight of pupal mass, length of hind tibia and number of adults emerged.