Comparative analysis of mosquito (Diptera: Culicidae: Aedes aegypti Liston) responses to the insecticide Temephos and plant derived essential oil derived from Piper betle L.

- Wild strains (WS) were compared with laboratory strains (LS) of Ae. aegypti for their resistance mechanisms.
- LS of Ae. aegypti were more susceptible against both the treatments of Pb-CVO and Temephos.
- WS of Ae. aegypti becomes resistant against Temephos but susceptible against Pb-CVO.
- Gut enzyme levels of LS and WS were altered significantly to both the treatments of Pb-CVO and Temephos.
- Photomicrography of gut regi.ons showed significant changes between the control and treated Ae. aegypti larvae of LS and WS.

Resistance to treatments with Temephos or plant derived oil, Pb-CVO, between a field collected Wild Strain (WS) and a susceptible Laboratory Strain (LS) of Ae. aegypti were measured. The Temephos (0.1 mg/L) showed the greatest percentage of mosquito mortality compared to Pb-CVO (1.5 mg/L) in LS Ae. aegypti. However, WS Ae. aegypti was not significantly affected by Temephos (0.1 mg/L) treatment compare to the Pb-CVO (1.5 mg/L). However, both strains (LS and WS) when treated with Pb-CVO (1.5 mg/L) displayed steady larval mortality rate across all instars. The LC50 of Temephos was 0.027 mg in LS, but increased in WS to 0.081 mg/L. The LC50 of Pb-CVO treatment was observed at concentrations of 0.72 and 0.64 mg/L for LS and WS strains respectively. The enzyme level of α- and β-carboxylesterase was reduced significantly in both mosquito strains treated with Pb-CVO. Whereas, there was a prominent deviation in the enzyme ratio observed between LS and WS treated with Temephos. The GST and CYP450 levels were upregulated in the LS, but decreased in WS, after treatment with Temephos. However, treatment with Pb-CVO caused both enzyme levels to increase significantly in both the strains. Visual observations of the midgut revealed cytotoxicity from sub-lethal concentrations of Temephos (0.04 mg/L) and Pb-CVO (1.0 mg/L) in both strains of Ae. aegypti compared to the control. The damage caused by Temephos was slightly less in WS compared to LS mosquito strains.

209