AbstractThe use of surfactants and their blends to improve the penetration of two insect growth regulators (IGRs; hydroprene and R-20458) into wheat kernels was investigated. It was found that formulation of IGRs with a surfactant, Tween-85 (polyoxyethylene trioleate), increased mortality and/or effectiveness of the IGRs. Formulation of hydroprene with a blend of Span-80 (sorbitan monooleate) with Tween-80 (polyoxyethylene monooleate) produced results comparable to those by hydroprene with Tween-85. However, formulations of IGRs with surfactants with high or low hydrophile-lipophile balance (HLB), failed to provide suitable control of the weevil, probably due to the type of emulsions formed. The same results were obtained with hydroprene formulations with blends of Spans and Tweens, even though their HLBs were close to that of Tween-85. Residual half-life for hydroprene was about three months; formulations with Tween-85 or a blend of Span-80 did not enhance the residual activity for hydroprene in wheat.
The effects of two insect growth regulators on the productivity of Rhyzopertha dominica, Sitophilus oryzae and S. granarius were studied by exposing insects to wheat treated with methoprene (isopropyl 11-methoxy-3,7,11-trimethyldodeca-2,4-dienoate) or hydroprene (ethyl 3,7,11-trimethyldodeca-2,4-dienoate) at concentrations of 1, 5, 10 and 20 ppm. Parental adult mortality was generally higher on wheat treated with methoprene than with hydroprene, and this effect was usually enhanced under unventilated conditions. The productivity of the three species was markedly reduced, in some instances suppressed, under unventilated conditions, whereas only R. dominica productivity was depressed under ventilated conditions. When progeny were produced, their productivity was, in general, lower than normal.
Effects of Five Insect Growth Regulators on Progeny Production, Productivity Index, Development, and Adult Emergence of the Rice Weevil, Sitophilus oryzae (L.) (Coleoptera : Curculionidae)