Susceptibility of immature stages of a biocontrol agent, Cheilomenes sexmaculata, to imidacloprid and pyriproxyfen

Abstract

Chemical control is one of the important strategies in agricultural pest management because of easy operation, availability and fast control of pests. On the other hand, the environment has been exposed to various types of pesticides and pollutants which are growing daily. The persistent effects of residual pesticides commonly used cause numerous problems for non-target organisms especially parasitoids and predators. In this research, the effects of pyriproxyfen and imidacloprid on Cheilomenes sexmaculata (F.) (Coleoptera: Coccinellidae) were studied. The eggs of the ladybird beetle were treated with each pesticide in three concentrations by dipping method. Maximum field recommended concentration (MFRC=50 mg/L), 2/1 MFRC (to simulate multiple treatments) and 1/2 MFRC (to test the sublethal effects) were used for pyriproxyfen and 1/1 MFRC (140 mg/L), 1/2 MFRC (70 mg/L) and 1/4 MFRC (35 mg/L) were used for imidacloprid. The highest mortality of the first instar larvae was observed in imidacloprid at MFRC and pyriproxyfen at 2/1 MFRC. Also, maximum influence on fertility was observed at 2/1 MFRC of pyriproxyfen and MFRC of imidacloprid with 55% and 44% reduction compared to the control, respectively. Moreover, pyriproxyfen caused significant retardation on larval development at concentrations higher than 1/2 MFRC. Both insecticides initiated a significant effects on adult eclosion compared to the control and the greatest influence was observed by imidacloprid at 1/1 MFRC with 89% reduction in adult eclosion. Although results revealed that imidacloprid has higher acute toxicity to C. sexmaculata, further results obtained from the analysis of on the life cycle parameters of C. sexmaculata also indicated that pyriproxyfen also had toxic effects on this predator.