Abstract

It has been argued that resistant cultivars may enhance the susceptibility of insect pests to insecticides, and thus can reduce crop production costs by lowering the rate of insecticide application. Here we studied the susceptibility of the cowpea seed beetle, Callosobruchus maculatus (Coleoptera: Chrysomelidae), reared on either a susceptible or resistant cultivar of the mung bean (Vigna radiate), to a herbal extract taken from the prickly parsnip, Echinophora platyloba (Umbelliferae). After selection of a susceptible (Parto) and a resistant (Sahar) cultivar, the median lethal concentration (LC50) of the herbal extract was determined as 24.41 and 20.28L/250mL air against beetles reared on susceptible and resistant cultivars, respectively. Rearing on resistant cultivar had a significant effect on biological parameters of C.maculatus regardless of insecticide application. However, herbal extract showed a significant interaction with host resistance in terms of oviposition rate and pre-adult development time. These results provide evidence that the resistant cultivar increases the susceptibility of C.maculatus to herbal extract. The use of plant resistance in combination with narrow-spectrum insecticides seems to be of both economic and environmental importance, as it can reduce the costs of crop production and lower the doses of insecticides required for satisfactory pest control.