BEHAVIOURAL AND PHYSIOLOGICAL ADAPTATIONS OF PEA APHIDS (HOMOPTERA: APHIDIDAE) TO HIGH GROUND TEMPERATURES AND PREDATOR DISTURBANCE

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Abstract
Pea aphids can avoid ladybug predators by dropping from the food plant when disturbed. Once off the plant the aphid must find another food plant. If temperatures on the ground are high, the aphid may die before finding a new food plant. In Kamloops, B.C., summers are hot and dry, compared with Vancouver where the climate is warm and moist. Pea aphids from Kamloops generally exhibit back-up behaviour and rarely drop from the plant when approached by a ladybug. By contrast, Vancouver pea aphids readily drop from the plant when disturbed by a predator. Adult aphids from Kamloops are more tolerant of heat under moist conditions at 37.5 °C than Vancouver adults but under dry conditions and at 42 °C, both groups have similar survival times. First instars of both aphid biotypes die sooner at high temperatures than adults. Mortality of aphids on the ground is sufficiently high to select against dropping behaviour as a first line defense against predators in areas with hot, dry climates.