The Nature of Genetic Variance Influencing Photoperiodic Diapause in a Migrant Insect, Oncopeltus fasciatus

Abstract

Female Oncopeltus fasciatus in long-day photoperiods lay eggs 15-20 days after their adult molt. Individual bugs transferred to short-day photoperiods extend age at first reproduction to about 80 days, but populations maintained in that same short-day condition show rapid decrease in extent of reproductive delay. Results from breeding experiments suggest that this decrease cannot be avoided, and those from parent-offspring comparisons for extent of reproductive delay in newly encountered short-day conditions indicate heritability of about 0.70. We suggest that the high level of additive genetic variance influencing female sensitivity to photoperiod functions as a "genetic rheostat" and results in eggs of the fall field population being optimally distributed geographically in the face of varying association between photoperiod and temperature. Genetic variance for the response is probably maintained by seasonally reversing selection pressures and by substantial genetic interchange among populations of this long-distance migrant.