| Summary: | The survival of aphids exposed to low temperatures is strongly influenced by their ability to move within and between plants and to survive exposure to potentially lethal low temperatures. Little is known about the physiological and behavioural limitations on aphid movement at low temperatures or how they may relate to lethal temperature thresholds. These questions are addressed here through an analysis of the thermal ecology of three closely related aphid species: Myzus persicae, a ubiquitous temperate zone pest, Myzus polaris, an arctic species, and Myzus ornatus, a sub-tropical species. Lower lethal temperatures (LLT(50)) of aphids reared at 15 degrees C were similar for M. persicae and M. polaris (range: -12.7 to -13.9 degrees C), but significantly higher for M. ornatus (-6.6 degrees C). The temperature thresholds for activity and chill coma increased with rearing temperature (10, 15, 20, and 25 degrees C) for all clones. For M. polaris and M. ornatus the slopes of these relationships were approximately parallel; by contrast, for M. persicae the difference in slopes meant that the difference between the temperatures at which aphids cease walking and enter coma increased by approximately 0.5 degrees C per 1 degrees C increase in rearing temperature. The data suggest that all three species have the potential to increase population sizes and expand their ranges if low temperature limitation is relaxed.
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