Phenotypic variability and heterozygosity at an esterase locus in the mosquito Aedes aegypti

Populations of the yellow fever mosquito, Aedes aegypti L. are polymorphic for esterase alleles. This could be because the alleles are neutral or because selection protects the polymorphism, as had been concluded from a study of allele frequencies. A test has been carried out to look for possible associations of esterase heterozygosity with speed of development, body size and spine number symmetry in two spine rows. Heterozygotes were found to be larger and slower growing than homozygotes, but there was no difference in degree of asymmetry. There were fewer heterozygotes and a greater deficiency compared with expectation in insects reared at higher temperatures. It is concluded that different genotypes do differ in fitness.