Effect of selection for dichlorodiphenyltrichloroethane (DDT) resistance on the uptake and breakdown of DDT in Aedes aegypti L.

Aedes aegypti larvae and adults were selected to high levels of resistance with dichlorodiphenyltrichloroethane (DDT) along separate lines. The larval-selected line showed three responses associated with larval resistance: (i) increased detoxication of DDT by dehydrochlorination to dichlorodiphenyldichloroethane DDE (demonstrated both in vivo and in vitro), (ii) increased tolerance to unmetabolised ("residual") DDT and, (iii) a reduction in uptake of DDT. Larval selection caused very little change in adult resistance or the uptake of DDT by adults, but there was an increase in dehydrochlorination. In the adult-selected line dehydrochlorination was increased by selection and was significantly correlated with resistance.Key words: DDT, DDE, resistance, Aedes aegypti.

An Integrated Study of the Factors Influencing the Choice of the Settling Site of Balanus crenatus Cyprid Larvae

Settled larvae of Balanus crenatus were collected at Pointe Mitis, in the St. Lawrence Estuary, Quebec. Four substrata were sampled and observed using scanning electron microscopy (SEM): shells of Mytilus edulis, fronds of Fucus evanescens, and laminated panels immersed for periods of 4 and 8 wk. Following this treatment, 23 variables describing the substratum surface, the cover of inert and biological material, and the gregarious response of the larvae were documented for 200 larvae, and compared with 187 control sites uncolonized by larvae. Significant differences of substratum texture, detritus, and diatom abundance were observed between colonized and uncolonized sites, indicating that the selectivity of the larva is related to the heterogeneity of the substratum. On all substrata, the settling site of the larvae was free of detritus and diatoms, clean surfaces ensuring better adhesion for the individual. To rank the variables on which selection occurred, the χ2 value of a contingency table between each variable and the type of substratum was computed. Variables carrying low χ2 values represented the most constant larval choices irrespective of the type of substratum. Variables related to the microscopic characteristics of the substratum were more important for larval selection than the variables describing the already established barnacle population.

THE INFLUENCE OF SEXUAL AND LARVAL SELECTION ON THE MAINTENANCE OF POLYMORPHISM AT THE SEPIA LOCUS IN DROSOPHILA MELANOGASTER

ABSTRACT Sexual selection is measured between two strains of Drosophila melanogaster: a wild strain and a strain mutant at the sepia locus. Frequencydependent male mating was found to be successful, whereas the female genotype exerted no influence. The rarer the male genotype becomes, the greater is its mating success. A selection model is built for this behavior characteristic in which selection operates differently in the two sexes. The genetic consequencies of this model upon the maintenance of genetic polymorphism at the sepia locus are compared to experimental data from previous population cage studies. The fit obtained with this sexual selection model is compared to that of the larval selection model previously investigated. A model composed of both sexual and larval components of fitness is presented. The role that each major selection component is expected to play in experimental populations as the gene frequency changes is discussed. Sexual selection leads to an equilibrium level higher than larval selection, and the combined model is very close to the experimental values.