QUANTITATIVE VARIATION AND HERITABILITY OF POSTDIAPAUSE DEVELOPMENT TIME AND BODY-SIZE IN THE ALFALFA LEAFCUTTING BEE (HYMENOPTERA, MEGACHILIDAE)

Quantitative variation of body size (measured by head width) and postd iapause development time were analyzed in Megachile rotundata (F.), fr om Albert, Canada. Data were collected from 200 nests. Nestmates, whet her male or female, were more similar to each other in each character than they were to individuals in other nests. Cellulose acetate electr ophoresis was used to estimate the relatedness among nestmates and it was found that the bees in each nest were mostly full siblings. Herita bility of body size, estimated using offspring-parent regression, was not significantly different from zero and was considerably lower than the estimate obtained by dividing the intraclass correlation by the re latedness. Because intraclass correlations can be inflated by environm ental variation, the difference between these two estimates implies th at maternal effects are the most important determinant of body size. H eritability of postdiapause development time could only be estimated u sing the intraclass correlation. In this case, the estimates were much higher than those for body size. Thus, although environmental sources must account for much of the variation, there appears to be a reasona ble heritable component for postdiapause development time. Therefore, with a combination of selection and manipulation of environmental cond itions, it should be possible to shift considerably the emergence time .