Behavioral responses of nine Aedes aegypti (L.) strains, six from recent field collections and three from the long-established laboratory colonies, were tested under laboratory-controlled conditions by using an excito-repellency test system. All nine strains showed significant behavioral escape responses when exposed to deltamethrin at the standard field dose (0.02 g/m2), regardless of background insecticide susceptibility status (susceptible or tolerant/resistant). Insecticide contact irritancy played a predominate role in overall female mosquito escape responses, whereas noncontact repellency was not observed at levels significantly different from paired noncontact control tests (P > 0.01). Among the six field populations, the Jakarta (Indonesia) Toba (north Sumatra), and Bangkok female mosquitoes showed rapid exit (>78%) during 30 min of direct contact with insecticide-treated surfaces, whereas the other three strains demonstrated only moderate escape responses (32–56%) from the chambers. Moderate escape responses during direct insecticidal contact also were observed in the three laboratory test populations (44–60%). Higher percentage of mortality was observed from laboratory strains (8–33%) that failed to escape compared with nonescape females of field strains (2–16%), possibly a reflection of background deltamethrin susceptibility status. We conclude that contact irritancy is a major behavioral response of Ae. aegypti when exposed directly to deltamethrin and that rapid flight escape from areas exposed to space sprays or surfaces treated with residual pyrethroids could have a significant impact on the effectiveness of adult mosquito control and disease transmission reduction measures.
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Vol. 41 • No. 6