Wash resistance and efficacy of three long-lasting insecticidal nets assessed from bioassays on Anopheles culicifacies and Anopheles stephensi

To test the wash resistance and efficacy of long-lasting insecticidal nets (LLINs), namely Olyset((R)) Net and PermaNet((R)) 2.0; and a long-lasting treatment kit, K-O Tab((R))1-2-3, on Anopheles culicifacies and An. stephensi, major malaria vectors in India, by bioassays. Conventionally treated deltamethrin net (CTDN with K-O Tab) was used for comparison. Mortality and median time for knockdown (MTKD) of mosquitoes were determined using contact bioassays and ball frame bioassays respectively. Hand washing and machine washing were used. LLINs showed good bio-efficacy against An. culicifacies and An. stephensi. The mortality of mosquitoes remained > 80% after up to 20 hand washes and up to 15 machine washes on all LLINs tested. No significant differences were observed in mortalities between the An. culicifacies and An. stephensi in cone bioassays (P > 0.05). MTKD increased progressively with successive washes and there was a significant difference in median time for knockdown of test mosquitoes and between hand-washed and machine-washed nets (P < 0.05). LLINs are more efficacious and last longer when washed by hand than by machine.