LABORATORY HYBRIDIZATION STUDIES OF ALLONEMOBIUS-FASCIATUS AND A-SOCIUS (ORTHOPTERA, GRYLLIDAE)

Allonemobius fasciatus (De Geer) and A. socius (Scudder) are small gro und-dwelling crickets that meet and hybridize, to a limited extent, in a mosaic contact zone stretching from New Jersey to at least as far w est as Illinois. To determine whether there is selection against hybri dization, we compared heterospecific and hybrid crosses with conspecif ic crosses with regard to offspring production, viability, and develop ment. Parental, F1, and F2 heterospecific and hybrid crosses produced considerable numbers of offspring, although some cross classes produce d significantly fewer offspring than conspecific crosses. Differences in the number of offspring produced between heterospecific or hybrid c rosses and conspecific crosses could be attributed to differences in t he number of eggs laid rather than to differences in the percentage ha tching. The time of hatching, the time required to reach adulthood, an d hatchling-to-adult survival were similar in the various cross classe s. Postzygotic barriers to gene exchange do not appear to be strong en ough to account for the low number of hybrids found in mixed populatio ns.