Studies on ecological impact of four IGR insecticides in adults of Hyposoter didymator (Hym., Ichneumonidae): pharmacokinetics approach

Adults of the parasitoid Hyposoter didymator were topically treated with four insect growth regulator (IGR) insecticides at different doses, including their respective maximum field recommended concentrations (MFRCs) [registered in Spain or recommended by manufacturers]. Methoxyfenozide and tebufenozide (100, 500 and 1,000 mg/l) did not affect any life parameter or the first parasitoid's offspring. In contrast, diflubenzuron (100, 500 and 1,000 mg/l) and pyriproxyfen (75, 500 and 1,000 mg/l) caused sublethal effects, decreasing the offspring emergence as a result of the parasitoid mortality during its immature stages inside the host and the life span of female offspring. In a second part, pharmacokinetic studies using a C-14 isotope of each IGR showed similar patterns of penetration through the cuticle, but different absorption and distribution rates inside the insect body. Cuticular penetration of pyriproxyfen reached about 99% in 3 days and those of diflubenzuron, methoxyfenozide and tebufenozide ranged from 82% to 86%. All insecticides were recovered from the reproductive system of insects and eggs. For pyriproxyfen and diflubenzuron absorption in the adult body tissues reach >65%, whereas this was only 40% for tebufenozide and methoxyfenozide. No statistical differences were found between sexes. The current data reflect that several mechanisms are likely to be involved in the selectivity of these products towards this parasitoid.