Larvicidal effectiveness of three controlled-release formulations of Dursban and Dimilin on Culex pipiens L. and Aedes aegypti (L.)

Abstract

SUMMARYThree plastic formulations of both Dursban and Dimilin were tested as controlledrelease pellets against larvae of C. pipiens and A. aegypti. Each pellet had an initial concentration of 0·116 μg/l. Results showed that Dimilin did not appear to give as high percentages of larval mortality as Dursban although in most cases a clearly delayed inhibition of adult emergence was noted. Larval mortalities of 90–100% were obtained in 3–14 (in the case of C pipiens) and 1–12 (in the case of A. aegypti) days when the second instar larvae were treated with Dursban formulations. With the Dimilin formulations no more than 31% (in case of C. pipiens) and 24% (in case of A. aegypti) larval mortalities occurred up to 13–14 days until completion of pupation.The results obtained showed that formulation 1 (polyvinyl chloride + dibutyl phthalate + toxicant) was the most effective of the three tested ones, followed by formulations 2 (polyvinyl chloride + dibutyl phthalate + triton X·100 + toxicant) and 3 (polyvinyl chloride + dibutyl phthalate + triton X·100 + ammonium carbonate + citric acid + water + toxicant), respectively. This was so on the basis both of percentage of larval mortality and time post-treatment. The durations of effectiveness of Dursban pellets were 123, 94 and 86 days for the formulations 1, 2 and 3 respectively. However, on the basis of number of tests with over 90% larval mortality, formulation 2 gave the highest level (13 tests) followed by formulation 3 (12 tests) and finally formulation 1 (10 tests). Therefore, consideration must be given to the cumulative effect of these factors of activity when using these formulations for control of mosquito larvae. Activity indices also proved that there was no definite variation in the toxicity of both DDT-susceptible and resistant strains against these formulations. Such results were obtained with Dimilin which confirmed that formulation 3 was the most effective one. The durations of effectiveness were about 112–115 (11–67% inhibition of adult emergence), 111–113 (11–93% inhibition of adult emergence) and 102–113 (12–100% inhibition of adult emergence) days for formulations 1, 2 and 3, respectively, for the susceptible and resistant lines of C. pipiens and A. aegypti.