Effects of the Insect Growth Regulators Methoxyfenozide and Pyriproxyfen on Adult Diapause in Sunn Pest Eurygaster integriceps (Hemiptera: Scutelleridae)

Sunn pest is a serious pest of cereals causing severe damage to the crop especially wheat. Its life cycle is comprised of two different phases, one is the growth and development phase and the other is diapause phase which takes place at the adult stage. In this study the effects of juvenile hormone analogue Pyriproxyfen, ecdysone analogue methoxyfenozide and a mixture of Pyriproxyfen plus methoxyfenozide on diapause termination of < 24-h-old-, 45day old- , and 90 day old adult Sunn pests were examined using topical application. Pyriproxyfen and a mixture of Pyriproxyfen plus methoxyfenozide induced the growth of the female reproductive organ whilst methoxyfenozide had no effect on adult diapause termination. Also, Pyriproxyfen failed to induce egg deposition in sexually immature adults of Sunn pest. Pyriproxyfen, methoxyfenozide and a combination of the two exerted no effect on the termination of diapause in < 24-h-old treated adult Sunn pests. However, Pyriproxyfen alone and a mixture of Pyriproxyfen plus methoxyfenozide successfully terminated reproductive diapause of 45, and 90 day old adult Sunn pests. Treatment of female only with Pyriproxyfen (10,000 ppm) induced termination of diapause and made egg-laying activity appear. However, egg number and percent of hatchability (27.6±7.5 and 9.77±4.89% respectively) were significantly lower than the treatment of both males as well as females with Pyriproxyfen (53.5±4.8 and 33.18±2.7% respectively) (P< 0.01). Treatment of the insect with these Insect Growth Regulators (IGRs) i.e. Pyriproxyfen and a combination of Pyriproxyfen plus methoxyfenozide produced significant differences in the egg and haemolymph protein concentrations, too. Thus, it is shown that these treatments affect vitellogenesis in Sunn pest.