Increased food utilization indices and decreased proteolytic activity in Helicoverpa armigera larvae fed sublethal Bacillus thuringiensis‐treated diet

Abstract

The cotton bollworm Helicoverpa armigera is one of the most devastating insect pests. A set of protease enzymes allows this species to feed on different host plant species. Control measures in agriculture often involve the application of the pathogenic bacterium Bacillus thuringiensis subsp. kurstaki (Btk). In the present study, the effects of sublethal Btk doses are evaluated with respect to the food utilization indices and proteolytic activities of Helicoverpa armigera. Accordingly, the H. armigera larvae are fed with artificial diet containing sublethal Btk doses (LC 5 , LC 10 , LC 15 , LC 20 and LC 25 ) and a Btk-free diet as control. All but one of the food utilization indices we measured is observed to increase significantly with increasing Btk doses. By contrast, the specific activity of total protease, chymotrypsin and elastase enzymes decrease significantly with an increasing Btk concentration. We conclude that Btk was not toxic to H. armigera larvae and any damage that it causes can be compensated for by H. armigera larvae via various mechanisms. In conclusion, increased nutritional indices in the larvae fed with Btk diet represent an important issue that needs to be considered to avoid the pest establishing Bt resistant populations. Meanwhile, the lack of effect of Btk sublethal concentrations on trypsin enzyme specific activity can bolster this challenge.

The effect of sublethal doses of Bacillus thuringiensis Berliner on Tuta absoluta (Meyrick) on resistant and susceptible tomato cultivars

“…Some studies have been conducted on the sublethal effects of Bt on various pests (Ghassemi-Kahrizeh, Aramideh, 2015;Fathipour et al, 2019;Fernandes et al, 2021;Poulin et al, 2022), Several studies have also been conducted on the effects of Bt on T. absoluta (Nozad-Bonab et al, 2017;Jamshidnia et al, 2018;Jalapathi et al, 2020). To our knowledge, there is not much information on the sublethal effects of Bt on T. absoluta, therefore, this study may provide more information on this issue.…”

Role of Microbial Biopesticides as an Alternative to Insecticides in Integrated Pest Management of Cotton Pests

“…Biopesticides are cheaper, take less time to develop [15], and are naturally less toxic to humans and the environment [16] compared with synthetic pesticides. They are mainly categorized into biochemical, plant, and microbial pesticides [17][18][19]. Biochemical pesticides include plant extracts, pheromones, plant and insect growth regulators that control pests by non-hazardous mechanisms [20].…”