Latitudinal Variation in the Photoperiodic Responses of Populations of Pea Aphid (Homoptera: Aphididae)

The purpose of this study was to determine if there is a latitudinal gradient in the photoperiodic responses of populations of pea aphid, Acyrthosiphon pisum (Harris). The approach was to measure photoperiodic responses of all clones at a standard photoperiod of 14:10 (L:D) at 20°C, and compare populations by making use of information on the relationship between photoperiod and the morphs of progeny produced and their sequence. Tests involved 90 clones from four latitudes, ranging from 44°45'N to 53°12′N. Results showed that the four populations differed from one another in their responses. The northerly clones generally gave short-day responses, and the southerly clones gave comparatively longer-day responses to the single test photoperiod.