Enhancing efficacy of Bacillus thuringiensis kurstaki against larvae of cowpea pod worm, Etiella zinckenella Treitschka (Lep., Pyralidae) utilizing a feeding stimulant

Abstract

The commercial microbial preparation Dipel 2X (Bacillus thuringiensis kurstaki) was tested against newly hatching larvae of the cowpea pod worm, Etiella zinckenella in 4 concentrations (1, 0.5, 0.25 and 0.125%) once alone and by adding sugar as feeding stimulant in two concentrations (0.25 and 0.125%). The larvae were reared on a modified semi-artificial diet based on cowpea seeds with other ingredients. Young green cowpea pods were sprayed with tested treatments and received eggs of the pest just prior to hatching. The newly hatching larvae showed an interesting behavior on the pods treated with Bt and sugar through lapping the sweet sprayed material on the pods for a period much longer than on pods treated with Bt alone prior to penetration by feeding with the chowing mouth parts. Thus, ingesting higher doses of the Bt spores and crystals leading to death of the larvae in high rates (98.3, 90, 86.6 and 71.6%) in case of adding 0.125& sugar. Meanwhile, these rates recorded 100% for the Bt concentrations of 1 and 0.5% mixed with 0.25% sugar on the fourth day post treatment.