Overcrowding Factors of Mosqutio Larvae X. Structure-Bioactivity Relationship and Bacterial Activation of the Alkyl-branched

To self-regulate the population density, mosquito larvae have been suggested to produce into their overcrwded environment n-heptadecane, n-octadecane, 7-methylocatadecane and 8-methylnonadencane, and 2-alkylfatty acids, which detard their growth and cause their high mortality. The present study on the structure-activity relationship with 20 new synthetic methyl-and ethyl-branched hydrocarbons showed that these require over 15-carbon-chain length to be effective against Culex pipiens molestus larvae and the optimum length is at 16-18 carbons.Bacterial incubation of these hydrocarbons activated the tosicity. The chemical analysis proved that the alkyl-branched hydrocarbons are decomposed slower than the strainght ones, and the metabolic branched fatty acids synergize the toxicity of the rsidual hydrocarbons. The mode of activation is presumably due to early exposure to the metabolic fatty acids of the younger larvae, while the intact hydrocarbons keep them growth-retarded and susceptible for a longer period. These findings also suggest genesis of the alkyl-branched fatty acids previously identified in the overcrowded mosquito culture from the coexisting branched hydrocarbons by bacterial decomposition.