Laboratory and field evaluation of the efficacy of four insecticides for Aedes vigilax (Diptera : Culicidae) and toxicity to the nontarget shrimp Leander tenuicornis (Decapoda : Palaemonidae)

Laboratory and field evaluations were conducted in southeastern Queensland, Australia, to determine the toxicities of 2 organophosphate compounds (tem ephos and pirimiphosmethyl), an insect growth regulator (s-methoprene), and Bacillus thurigiensis variety israelensis de Barjac (Bti) to Aedes vigilax (Skuse), an Australian saltmarsh mosquito vector of Ross River virus. The toxicity of these compounds to Leander tenuicornis Say, a cohabiting nontar get shrimp species, was also assessed, s-Methoprene and Bti were found to b e the most selective for Ae. vigilax with selectivity ratios (LC95 nontarge t/LC95 target) of 255,000 and 38,000, respectively. In contrast, selectivit y ratios of 13 and 0.01 were calculated for temephos and pirimiphos-methyl, respectively. As predicted by the laboratory studies, the field applicatio ns of s-methoprene and Bti were highly effective against Ae. vigilax, while not affecting L. tenuicornis survival. In contrast, although temephos and pirimiphos-methyl were both effective against Ae. vigilax, these products a lso killed 100% of caged L. tenuicornis. s-Methoprene and Bti did not affec t water quality, whereas temephos and pirimiphos-methyl significantly influ enced pH and turbidity. Accordingly, based on the high selectivity ratios, excellent field efficacy, and lack of influence on abiotic water characteri stics, s-methoprene and Bti were ideal for insecticide control of Ae. vigil ax in Australian saltmarsh pools.