Submitted to: Journal of the American Mosquito Control Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/4/2009
Publication Date: 10/30/2009
Citation: Allan, S.A., Kline, D.L., Walker, T. 2009. Environmental factors affecting efficacy of bifenthrin treated vegetation for mosquito control. Journal of the American Mosquito Control Association. 25(3):338-346. Interpretive Summary: Due to their nuisance status and ability to serve as vectors of West Nile Virus, St. Louis encephalitis and Eastern Equine encephalitis, mosquitoes are targeted for control efforts across North America. Targeted application of residual pesticides on vegetation in residential and recreation areas is an effective method for killing mosquitoes while they rest during part of the day. In this study, conducted by scientists at CMAVE, the extent that environmental factors affect the degradation of backpack or electrostatically applied treatments of bifenthrin on wax myrtle and azaleas were examined. This information provides the basis for strategies that optimize the efficacy of residue-treated vegetation for mosquito control.
Technical Abstract: The use of pesticide-treated vegetation as a barrier for control of nuisance and disease-bearing mosquitoes has become an option for mosquito management for home owners, public health and mosquito control professionals. Potted wax myrtle and azalea plants were treated with bifenthrin (0.79% AI) at maximum label rate using backpack and electrostatic sprayers and exposed to various treatments that could affect the residual degradation of the applied pesticides. Treatments included leaf aspect, simulated rainfall, shade or natural sun exposure with the residual effectiveness of leaves examined in tarsal contact petri dish assays using laboratory-reared Aedes aegypti. There was no significant difference in efficacy between the adaxial (top) or abaxial (bottom) surfaces of electrostatically- or backpack-treated leaves. Significant differences existed between application method, plant species and exposure with most significant effects between week 1 and 4. Simulated heavy rainfalls applied three times weekly reduced knockdown of leaves treated with electrostatic and backpack methods with reductions seen as soon as 1 week after treatment. Reductions were seen with both wax myrtle and azalea leaves and seen after 1, 4 and 24 hour contact of mosquitoes to leaves. Placement of plants with full exposure to sunlight also significantly reduced efficacy compared to plants placed in the shade. Differences were observed most often for 4 and 24 h knockdown counts and significant decreases were seen from week 4 onwards. Clearly factors such as rain and exposure to sun impact degradation of efficacy of bifenthrin-treated vegetation in the field. Degradation of bifenthrin efficacy was slowest in sites protected from rain and sun which coincide with preferred resting site locations for many mosquito species.