Effects of spirotetramat and chlorpyrifos on the functional response of Aenasius bambawalei Hayat

Phenacoccus solenopsis Tinsley is a polyphagous pest that has become a serious threat to agriculture in the tropical and subtropical regions of the world since the beginning of the twentieth century. Aenasius bambawalei Hayat is an endoparasitoid that parasitizes third instar nymphs of P. solenopsis. In this study, sublethal effects of spirotetramat and chlorpyrifos were investigated on the functional response of the parasitoid on the nymphs of P. solenopsis at 27± 1 ° C, 65± 5% RH, and a photoperiod of 14: 10 (L: D). The densities of 2, 4, 8, 16, 32, and 64 third instar nymphs of P. solenopsis were used in the experiments. The results of logistic regression showed type II functional response in all three treatments including control, spirotetramat, and chlorpyrifos. The search rate (a) of the wasp in control, spirotetramate, and chlorpyrifos treatments were calculated to be 0.2609, 0.1107, and 0.0556 h–1, respectively, which in spirotetramat, and chlorpyrifos were 57% and 78% less than control. Handling time (Th) in control, spirotetramat, and chlorpyrifos treatments were calculated to be 0.0187, 6.3352, and 9.3903 h, respectively. In spirotetramate and chlorpyrifos treatments, handling times were about 26% and 87% more than control. The handling rates of control, spirotetramate, and chlorpyrifos were 4.63, 3.28, and 2.55 host nymphs, respectively; which in spirotetramate and chlorpyrifos it was 31% and 45% less than in control. The results of this study showed that the insecticides of spirotetramate and chlorpyrifos had a negative effect on the functional response behavior of the parasitoid even at low doses and thus could disturb the biological control.