Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 9, 2009
Publication Date: N/A
Interpretive Summary: Residual pyrethroid insecticides are increasingly being used to treat walls and curtains inside homes, and vegetation barriers outdoors as a means of personal protection against mosquitoes. Unlike insecticide-treated bednets, these treated surfaces require mosquitoes to land on when alternative untreated surfaces are available, and in the absence of an attractant. Laboratory tests usually involve forced contact with treated surfaces, or contact with treated nets with an attractant behind them. We are not aware of any study that examines facultative contact, which more resembles the real world where there are numerous untreated surfaces available as alternative landing sites, and no attractant incentive for landing. This manuscript investigates facultative landing behavior of three medically important species of mosquito, in three genera, presented with pyrethroid-treated and adjacent untreated surfaces, and no added attractant incentive for landing. A detailed analysis was conducted by scientists at the USDA, ARS, Center for Medical, Agricultural, and Veterinary Entomology, Mosquito & Fly Research Unit in Gainesville, FL, on landing and resting behaviors, and our findings revealed each species and pyrethroid resulted in different behavioral patterns. We discuss the findings with regard to the use of the term “excito-repellency”, around which there has been considerable confusion in the literature. We attempt to clarify the confusion surrounding this term, and suggest an alternative more descriptive term for what is happening behaviorally.
Technical Abstract: Mosquitoes from three genera, Aedes aegypti L., Anopheles quadrimaculatus Say, and Culex quinquefasciatus Say were tested for facultative landing and resting behavior on pyrethroid-treated surfaces paired with adjacent untreated surfaces. The three pyrethroids tested were bifenthrin, deltamethrin, and lambda-cyhalothrin. Landing and resting behavior was video recorded and quantified using Observer XT software. Untreated control treatments were tested to reveal behavior in the absence of insecticides. In controls the three species had different activity levels, with An. quadrimaculatus being the most active and Cx. quinquefasciatus being the least active. The three species had unique responses to different compounds tested. Landing frequency on adjacent untreated and treated filter papers did not differ for any compound or species, at any time during the experiment. However, landing frequencies did differ between treatments and over time. Differences between treated and untreated sides were largely due to changes in the length of time mosquitoes rested on each side. An. quadrimaculatus had a unique response to the presence of deltamethrin compared to the other species or compounds in which it spent an increased amount of time in contact with both treated and adjacent untreated surfaces. Cx. quinquefasciatus, avoided all three compounds by the end of the experiment and rested longer on untreated sides. In most cases, modification of landing and resting behaviors occurred only after mosquitoes had the opportunity to come into contact and acquire a dose of pyrethroid. Bifenthrin had the fastest KD50 for all species. Other differences between compounds for each species are described. The term “excito-repellency” has produced confusion in the literature, and it is revisited and discussed with respect to the results, which justify the use of alternative terminology. The term “locomotive stimulant” is offered as an acceptable alternative.