LOW-VOLUME APPLICATION BY MIST-BLOWER COMPARED WITH CONVENTIONAL COMPRESSION SPRAYER TREATMENT OF HOUSES WITH RESIDUAL PYRETHROID TO CONTROL THE MALARIA VECTOR ANOPHELES-ALBIMANUS IN MEXICO

Village-scale trials were carried out in southern Mexico to compare th e efficacy of indoor-spraying of the pyrethroid insecticide lambda-cyh alothrin applied either as low-volume (LV) aqueous emulsion or as wett able-powder (WP) aqueous suspension for residual control of the princi pal coastal malaria vector Anopheles albimanus. Three indoor spray rou nds were conducted at 3-month intervals using back-pack mist-blowers t o apply lambda-cyhalothrin 12.5 mg a.i./m(2) by LV, whereas the Wp was applied by conventional compression sprayer at a mean rate of 26.5 mg a.i./m(2). Both treatments caused mosquito mortality indoors and outd oors (collected inside house curtains) as a result of contact with tre ated surfaces before and after feeding, but had no significant impact on overall population density of An. albimanus resting indoors or asse ssed by human bait collections. Contact bioassays showed that WP and L V treatments with lambda-cyhalothrin were effective for 12-20 weeks (> 75% mortality) without causing excite-repellency. Compared to the WP t reatment (8 houses/man/day), LV treatment (25 houses/man/day) was more than 3 times quicker per house, potentially saving 68% of labour cost s. This is offset, however, by the much lower unit price of a compress ion sprayer (e.g. Hudson 'X-pert' at US$120) than a mist-blower (e.g. 'Super Jolly' at US$350), and higher running costs for LV applications . It was calculated, therefore, that LV becomes more economical than W P after 18.8 treatments/100 houses/10 men at equivalent rates of appli cation, or after 7.6 spray rounds with half-rate LV applications.