Incorporation of lyophilized leaves and pods into artificial diet to assess antibiosis component of resistance to pod borer in pigeonpea

Helicoverpa armigera, is the most damaging insect pest of grain legumes including pigeonpea in the semi-arid tropics, and host plant resistance is an important component for the management of this pest. Because of the variation in insect density over space and time, it is difficult to assess the contribution of different components of resistance to this insect under field conditions. Therefore, we standardized a bioassay involving incorporation of lyophilized leaves or pods into the artificial diet to assess antibiosis component of resistance to H. armigera. Antibiosis was assessed in terms of larval mortality, larval and pupal weights, adult emergence, and duration of development on fresh leaves, flowers and pods, and through incorporation of lyophilized leaves and pods of different pigeonpea genotypes into the artificial diet. Incorporation of 10 g of lyophilized leaf or pod powder into the artificial diet (300 ml) of diet resulted in maximum differences in survival and development of H. armigera larvae on the resistant (ICPL 332) and susceptible (ICPL 87) genotypes. Reduced larval and pupal weights, and prolongation of larval and pupal development periods were observed in insects reared on intact leaves or pods of ICPL 332, ICPL 84060, ICP 7035, ICPL 88039 and T 21. Similar effects were also observed in larvae reared on artificial diet impregnated with lyophilized leaves or pods of ICPL 332, ICPL 84060, ICP 7035, ICPL 187-1, ICPL 88039, and ICP 7203-1. Larval and pupal periods, pupal weight, and pupation and adult emergence were positively correlated between the insects reared on fresh leaves or pods, and on artificial diets impregnated with lyophilized leaves or pods. However, there was no correspondence in terms of larval weight and mortality between the fresh plant parts and diet impregnation assay. Incorporation of lyophilized leaves or pods of pigeonpea into artificial diet for assessing the antibiosis component of resistance to H. armigera has been discussed