Cytochrome P450 monooxygenases play a key role in pest resistance to insecticides by detoxification. Four new P450 genes, CYP6AS160, CYP6AS161, CYP4AB73 and CYP4G232 were identified from Solenopsis invicta. CYP6AS160 was highly expressed in the abdomen and its expression could be induced significantly with exposure to fipronil, whereas CYP4AB73 was not highly expressed in the abdomen and its expression could not be significantly induced following exposure to fipronil. Expression levels of CYP6AS160 and CYP4AB73 in workers were significantly higher than that in queens. RNA interference-mediated gene silencing by feeding on double-stranded RNA (dsRNA) found that the levels of this transcript decreased (by maximum to 64.6%) when they fed on CYP6AS160-specific dsRNA. Workers fed dsCYP6AS160 had significantly higher mortality after 24 h of exposure to fipronil compared to controls. Workers fed dsCYP6AS160 had reduced total P450 activity of microsomal preparations toward model substrates p-nitroanisole. However, the knockdown of a non-overexpressed P450 gene, CYP4AB73 did not lead to an increase of mortality or a decrease of total P450 activity. The knockdown effects of CYP6AS160 on worker susceptibility to fipronil, combined with our other findings, indicate that CYP6AS160 is responsible for detoxification of fipronil. Feeding insects dsRNA may be a general strategy to trigger RNA interference and may find applications in entomological research and in the control of insect pests in the field.

Spodoptera litura is a widespread polyphagous insect pest that can develop resistance and cross-resistance to insecticides, making it difficult to control. Insecticide exposure has previously been linked with induction of specific olfactory-related proteins, including some chemosensory proteins (CSPs) and odorant-binding proteins (OPBs), which may disrupt detection of environmental factors and reduce fitness. However, functional evidence supporting insecticide and OBPs/CSPs mediation remains unknown. Here we fed male S. litura moths with sucrose water containing one of three insecticides, chlorpyrifos, emamectin benzoate or fipronil, and used real-time quantitative polymerase chain reaction and RNAi to investigate OBPs and CSPs expression and their correlations with survival. Chlorpyrifos and emamectin benzoate increased expression of 78% of OBPs, plus 63 and 56% of CSP genes, respectively, indicating a major impact on these gene families. RNAi knockdown of SlituCSP18, followed by feeding with chlorpyrifos or fipronil, decreased survival rates of male moths significantly compared with controls. Survival rate also decreased significantly with the downregulation of SlituOBP9 followed by feeding with chlorpyrifos. Thus, although these three insecticides had different effects on OBP and CSP gene expression, we hypothesize that SlituOBPs and SlituCSPs might mediate their effects by increasing their expression levels to improve survival. Moreover, the differential response of S. litura male moths to the three insecticides indicated the potential specificity of chlorpyrifos affect SlituCSP18 and SlituOBP9 expression.

Hirstiella spp. are common ectoparasites of captive green iguanas (Iguana iguana). Suggested treatments are empirical and some of them are of low efficacy and potentially toxic. The objective of this open-label study was to investigate the short-term efficacy and safety of a single application of 0·25% fipronil solution for the treatment of hirstiellosis. The skin of 50 green iguanas was thoroughly examined with the aid of bright light and magnifying lenses. A total of 21 iguanas were found to be infested, harbouring 1–24 mites (median: 5). All 35 mites collected from 17 iguanas were identified as Hirstiella sp. Both infested and non-infested lizards, sharing the same enclosure, were carefully wiped with 0·25% fipronil solution. The safety and the efficacy of the treatment were evaluated after 2 days in 47/50 (94%) and 7 days in 29/50 (58%) iguanas. Compared with pre-treatment levels, the parasitic load did not changed significantly on the second day but was significantly lower on day 7 (P = 0·006). No adverse reactions were noticed. Based on these results a single whole-body application of 0·25% fipronil solution can be considered a safe and effective treatment for the reduction of parasitic burden in captive green iguanas infested by Hirstiella sp. mites.