Influence of midgut bacteria on toxicity of Bacillus thuringiensis to pink bollworm, Pectinophora gossypiella (Lepidoptera: Gelechiidae)

Gut bacteria play pivotal role in many aspects of insects’ growth and development. They are generally beneficial but, can turn out to be harmful under certain conditions. Synergism/potentiation of Bacillus thuringiensis (Bt) efficacy in many insect species is one such instance, where it is harmful to insect but is of immense value for their management using Bt toxins directly or indirectly. In the present study, commercial formulation of Bt (DiPel®) and Cry1Ac and Cry2Ab toxins were evaluated using five concentrations against five-day old larvae of Pectinophora gossypiella with and without antibiotics (which removed the gut bacteria) by diet incorporation method. Lowest median lethal concentration (LC50) was recorded in Cry2Ab (1.49 µg/gm of diet) followed by Cry1Ac (2.54 µg/gm of diet) and DiPel® (3.63 µg/gm of diet) without the antibiotics (AB). Whereas, highest LC50 (9.38 µg/gm of diet) was recorded with DiPel® + AB (chloramphenicol and tetracycline at 50 µg/gm of diet each) followed by Cry1Ac + AB (4.73 µg/gm of diet) and Cry2Ab + AB (3.66 µg/gm of diet). These results showed that DiPel® as well as both the Cry toxins along with antibiotics were less toxic to larvae of P. gossypiella thus indicates that gut bacteria potentially affect the susceptibility to Bacillus thuringiensis.