Effects of acclimation and latitude on the activity thresholds of the aphid Myzus persicae in Europe

Activity thresholds were measured in nine anholocyclic clones of the peach-potato aphid Myzus persicae collected along a latitudinal cline of its European distribution from Sweden to Spain. The effects of collection origin and intra- and intergenerational acclimation on these thresholds were investigated. Low-temperature (10 degrees C) acclimation for one generation depressed the movement threshold and chill coma temperatures, with the largest reduction in movement threshold recorded for clone UK 1 (8.82.5 degrees C) and in chill coma for UK 2 (4.82.0 degrees C). High-temperature (25 degrees C) acclimation for one generation increased the heat movement threshold and heat coma temperature with the largest increase in the movement threshold (40.141.1 degrees C) and heat coma (41.442.3 degrees C) recorded for clone Swed 1. There was no further intergenerational acclimation over three generations. High-temperature activity thresholds were less plastic than low-temperature thresholds, and, consequently, thermal activity ranges were expanded following low-temperature acclimation. No constant affect of acclimation was observed on chill coma recovery, although clonal differences were observed with Swed 1 and 3 requiring some of the longest complete recovery times. There was no relationship between latitude and activity thresholds with the exception of heat coma data where Scandinavian clones Swed 2 and 3 consistently displayed some of the lowest heat coma temperatures (e.g. 41.3 degrees C for both clones at 20 degrees C) and Mediterranean clones Span 1, 2 and 3 displayed some of the highest (e.g. 42.1, 41.9 and 42.5 degrees C, respectively, at 20 degrees C). These data suggest that clonal mixing could occur over a large scale across Europe, limiting local adaptation to areas where conditions enable long-term persistence of populations, e.g. adaptation to higher temperatures in the Mediterranean region. It is suggested that aphid thermal tolerance could be governed more by clonal type than the latitudinal origin.