The extent of genetic differentiation between native and groundnut-feeding forms of the groundnut seed beetle Caryedon serratus Olivier was studied. Sixteen samples (560 individuals of both sexes collected in four localities in Senegal) of C. serratus were reared from pods of four distinct host plants (Arachis hypogaea L., Bauhinia rufescens Lam., Piliostigma reticulatum (DC) Hochst and Tamarindus indica L.), and five microsatellite loci were analysed. Phylogenetic and statistical analyses indicated that host plants strongly influence the degree of genetic differentiation between sampled individuals. Within host plants, genetic differentiation was low. Genetic differentiation between hosts was highly significant (average θ = 0.374) and geographical distances between localities did not influence the genetic structuration of C. serratus populations from a given host plant. The results of this study show that C. serratus could be under a host race formation process.

To investigate the existence of inter-strain fecundity in the groundnut beetle Careydon serratus, the fecundity and larval survival of crosses of beetle strains from Bauhinia, Cassia, Piliostigma and Tamarindus were studied. The crosses produced viable eggs, but the fertility of beetles mated within strains was significantly higher than that of inter-strain matings, the former being nearly double the latter. Differences in larval mortality between the various crosses were also observed.

Starch gel electrophoresis was used to compare eight loci in six enzymatic systems of 17 samples of the groundnut seed-beetle, Caryedon serratus (Ol.) (Coleoptera: Bruchidae) bred on five different host-plant species: Arachis hypogaea, Bauhinia rufescens, Cassia sieberiana, Piliostigma reticulatum and Tamarindus indica. The rate of polymorphism was 44.8%. The average genetic diversity (Hw) was 0.184. Allozyme variability analysis indicated that seed-beetles associated with P. reticulatum and groundnut, Arachis hypogaea were genetically similar, whereas other samples clustered according to their host plant species. Geographical distances less than 400 km were not decisive for the genetic structuring of samples associated with a given host plant.