Impact of a Bifenthrin-Treated Lethal Ovitrap on Aedes aegypti Oviposition and Mortality in North Queensland, Australia

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Abstract
Lethal ovitraps (LOs) containing an insecticide-treated ovistrip are used as a lure-and-kill device for the container-breeding dengue vector, Aedes aegypti (L.). We aimed to affirm that the pyrethroid bifenthrin could be used effectively in LOs against Ae. aegypti in north Queensland, Australia, by quantifying oviposition in and mortality caused by LOs. Small cage experiments in which individual gravid Ae. aegypti were given a choice of LOs and untreated ovitraps revealed that although LOs were less acceptable for oviposition, they provided an average 64.6% adjusted mortality. Although 92% of mosquitoes ovipositing in LOs died, 61.8% of mosquitoes that visited but did not oviposit in an LO also died, demonstrating that lethal contact occurred without egg laying. The bifenthrin content of strips (approximately 0.1 mg/cm2; 7 mg/strip) did not decrease significantly after 4 wk of field exposure nor did the toxic effect of the LOs. Large cage trials with groups of 10 Ae. aegypti confirmed that bifenthrin-treated LOs provided consistent control (average adjusted mortality 79.7%). Four-week field trials in north Queensland showed that although LOs were acceptable to ovipositing Ae. aegypti (mean time to first egg 10.9 d; mean eggs 47.3), insecticide-free ovitraps were oviposited in more readily (6.8 d, 199 eggs). The number of eggs laid per mosquito in laboratory LOs allowed calculation of the number of Ae. aegypti killed in field-deployed LOs; rapid estimates can be made by simply dividing the number of eggs on the strip by 2.84. Overall, the studies demonstrated that bifenthrin-treated LOs have potential for use as a lure-and-kill device against Ae. aegypti and that they should be effective in the field for at least 4 wk. Given that untreated ovitraps were more acceptable for Ae. aegypti oviposition, the removal of alternative oviposition sites before deployment of LOs in the field should maximize their effectiveness.