Sublethal effects of Beauveria bassiana sensu lato isolate NJBb2101 on biological fitness and insecticide sensitivity of parental and offspring generations of brown planthopper, Nilaparvata lugens

Abstract

Entomopathogenic fungi such as Beauveria bassiana sensu lato (s. l.) have been developed for biological control of sucking insect pests such as Nilaparvata lugens. However, the sublethal effects of B. bassiana s. l. on N. lugens remain unclear, and were investigated in the present study. N. lugens 3rd instar nymphs were inoculated with a sublethal concentration of B. bassiana s. l. isolate NJBb2101 conidia and then reared until they developed into adults. The resultant adults (parental generation) were paired to generate offspring. Life parameters in both the parental and the offspring generations were examined: nymph survival rate, emergence rate, nymph duration, sex ratio, copulation rate, fecundity, hatching rate and adult female longevity. Compared with the control, NJBb2101-treated N. lugens exhibited lower fitness indices such as low female ratio and fecundity, with the relative fitness of offspring being only 0.28. Both generations of NJBb2101-treated N. lugens were much more susceptible to three test insecticides with susceptibility increasing by 12.7–23.3-fold in parental females and 3.8–8.4-fold in the offspring (4th instar nymphs and females). The results suggest that sublethal effects of entomopathogenic fungi on N. lugens can reduce insect growth and development and increase insecticide susceptibility. The findings are of practical interest for pest insect management in terms of combining entomopathogenic fungi with chemical insecticides.