Effects of brief exposures to low temperature on the development, longevity and fecundity of the grain aphid Sitobion auenae (Hemiptera: Aphididae)

First instar nymphs and adults of the grain aphid Sirobion auenae that had been reared at 10°C and 20°C over a number of generations, were cooled to -5°C and -10°C for 1 h and 6 h and returned to 20°C to assess the effects of brief exposures to low temperatures (cold-pulses) on their survival. rate of development, longevity and fecundity. A strong acclimation response was observed in first instar nymphs, with significantly less mortality in groups reared to 10°C compared to 20°C. Mean development time from first instar to adult was not significantly affected by low temperature exposure at the first nymphal stage. Longevity in all groups cooled as first instars was reduced by the sub-zero cold-pulses, and was also dependent on temperature and exposure time. Acclimated aphids survived longer than non-acclimated individuals. Reproductive rate, in terms of the number of nymphs born per aphid per day, was unaffected by cold stress applied at the first instar stage. Total fecundity was however reduced, being a function of the number and longevity of the survivors. Adult aphids were less cold hardy than nymphs; mortality was higher at -10°C than -5°C increasing with duration of exposure from 1 h to 6 h. Mean fecundity was reduced significantly in aphids cooled at the adult stage, the number of aphids born per day decreasing as the exposure period of the cold-pulse increased, suggesting that low temperature had affected embryogenesis. All the nymphs born to adults surviving exposure to -5°C for 6 h died within 48 h of birth, indicating that low temperature has a pre-natal effect on mortality.