Photoperiodic responses of phenologically aberrant populations of pierid butterflies (Lepidoptera)

Two local pierid populations in western North America showing regionally aberrant phenologies were investigated in the laboratory. Neither a partially bivoltine Pieris napi from the Sierra Nevada foothills in El Dorado County, California (surrounded by univoltine populations), nor a vernal-univoltine P. occidentalis from a foothill outlier of the Colorado Front Range (below bivoltine populations) showed unusual responses to controlled developmental regimes in the laboratory. Their unusual phenologies are hypothesized to be the product of microclimate. Failure to undergo genetic adaptation to unusual microclimates is discussed with particular reference to the presence or absence of gene flow from nearby normal populations.