Residual effectiveness of pyrethroid-treated foliage against adult Aedes albopictus and Culex quinquefasciatus in screened field cages.

The residual effectiveness of pyrethroid-treated foliage as a barrier against female Aedes albopictus and Culex quinquefasciatus was evaluated in large screened cage field tests. Individual potted southern wax myrtle, Myrica certifica, plants were treated with either Aqua Reslin 20 + 20 emulsifiable concentrate (EC) (20% active ingredient [AI] permethrin + 20% [AI] piperonyl butoxide), Permanone EC (10% [AI] permethrin), or Suspend suspension concentrate (SC) (4.75% [AI] deltamethrin) at maximum label rates. Generally, Aqua Reslin provided -83% overall reduction of mosquitoes during the week of treatment. After that time, mosquito reduction decreased to <50% and continued at this level for the remainder of the 12-wk study. Mosquito knockdown/mortality from excised Aqua Reslin-treated leaves revealed that this formulation quickly lost effectiveness after the initial week of treatment. Plants treated with Permanone provided =70% and 64% overall reduction during the week of, and first week after treatment, respectively. Knockdown/mortality from excised leaf bioassays of leaves treated with this formulation fell below 50% 2 wk after treatment where it remained for the rest of the study. Suspend generally provided 70 to approximately 80% overall mosquito reduction during the first 4 weeks after treatment and decreased to <50% thereafter. Residues on treated leaves provided >95% overall knockdown/mortality throughout the study and was not correlated with weekly reduction in the field cages. We believe this disparity was in part attributed to new plant growth. Newly formed leaves probably provided nontoxic surfaces for mosquito harborage.