Approximation to the CDC method to determine insecticide susceptibility in leishmaniasis vectors.

Abstract

The Centers for Disease Control (CDC, USA) has proposed a simplified method for the determinations of insecticide resistance in adult mosquitoes, using 250 ml Wheaton bottles containing measured dosages. Insects are transferred into the bottle for 1 hour and monitored for mortality at regular intervals. In standardizing the CDC method for use with phlebotomine sand flies, effects of the solvent without insecticide were evaluated. Two colonized sand fly vector species were used: Lutzomyia longipalpis (F50 and F54) and Lutzomyia serrana (F17). Groups of 10 to 24 unfed females 1-3 days old were transferred for 1 h to Wheaton bottles with the following pretreatment: (1) without additive, (2) 0.5 ml of acetone, or (3) 1.0 ml of acetone. Three to 5 replicates were undertaken for each condition and each species. In the control bottles, the insects rested quietly and after 1 h appeared normal. In bottles with 0.5 and 1.0 ml acetone, a repellent effect was observed in L. longipalpis and L. serrana within the first 10 min. A small proportion of the L. serrana became prostrate, but recovered quickly after removal from the bottle. Field test performed with Lutzomyia quasitownsendi produced results simialar to those of the L. serrana colony flies. The insecticide bioassays were performed with L. longipalpis (F60) flies. Females were exposed to three graded doses of lambdacyhalothrin (10, 50 and 100 micrograms/bottle), and mortality was recorded at five-minute intervals. Regression lines for the 3 concentrations were compared within the context of the CDC method. The advantages of the CDC method over the WHO protocols were four: lower cost, fewer insects required, an entire group of insects exposed to the same surface, and ease of field use.