Toxicity of spinosad to temephos-resistant <i>Aedes aegypti</i> populations in Brazil

<div><p>The mosquito <i>Aedes aegypti</i> is the primary vector of different arboviruses and represents a major public health problem. Several Brazilian populations of <i>Ae</i>. <i>aegypti</i> have developed resistance to temephos, the most used organophosphate larvicide. New tools which are less harmful to the environment and safer for humans are becoming increasingly important to control this insect vector. Spinosad, an aerobic fermentation product of a soil actinobacteria, has a favorable environmental profile. It presents selective insecticide properties, a mechanism of action that differs from those of many synthetic chemical insecticides. The toxicity of spinosad and temephos to <i>Aedes aegypti</i> populations from Brazil, which were previously exposed to temephos, were investigated in this study. Larval susceptibility (LC50) to temephos varied from 3μg/L for Rockefeller up to 260 μg/L for Santana do Ipanema field derived population. Larval susceptibility (LC50) to spinosad varied from 23μg/L for Rockefeller up to 93μg/L for Marilia field derived population. In addition, a semi-field trial was performed to evaluate spinosad (Natular^TM DT) initial efficacy and persistence toward four field-derived lineages and the Rockefeller lineage, used as an internal control. Spinosad was tested at 0.5mg active ingredient/L in 200L capacity water tanks. Mortality was recorded each 24 hours after exposition and tanks were further recolonized once per week with mortality being recorded daily for eight weeks. Spinosad provided a level equal or superior to 80% mortality during a seven to eight week evaluation period. The assessed populations did not present cross-resistance between spinosad and temephos in laboratory conditions. It demonstrates that spinosad may be a promising larvicide for the control of <i>Ae</i>. <i>aegypti</i>, especially for populations in which resistance to temephos has been detected.</p></div

Toxicity of temephos and spinosad against 3rd instar <i>Aedes aegypti</i> larvae after a 24h exposure.

<p>Toxicity of temephos and spinosad against 3rd instar <i>Aedes aegypti</i> larvae after a 24h exposure.</p

Field evaluation of Spinosad (Natular^TM DT) against <i>Aedes aegypti</i> 3rd instar larvae.

<p>The average mortality percentage is represented for three independent bioassays conducted in a row, A- Rockefeller, Marilia and Salvador (tested between July 2011 and February 2012). B- Rockefeller, Goiânia and Santarém (tested between September 2011 and November 2012). C- pH and temperature of the solution in the tanks during the three assays for the Rockefeller, Marilia and Salvador group. D- pH and temperature of the solution in the tanks during the three assays for the Rockefeller, Goiânia and Santarém group. The dose tested was 0.5mg/L. Every week the tanks were recolonized by removing the dead and the remaining living larvae and introducing 30 new 3rd instar larvae.</p