Effects of sublethal cold stress on the aphid Rhopalosiphum padi.
Abstract
An anholocyclic clone of Rhopalosiphum padi was reared on leaves of barley seedlings at 20°C in LD 16:8. First-instar nymphs and newly moulted, pre-reproductive adults were cooled at 1°C/min to -5 and -7.5°C, resp., for 1 and 6 h to inflict increasing sublethal cold stress. Surviving aphids were returned to 20°C and LD 16:8, after which observations were made on the rate of nymphal development, adult reproduction and longevity, and survival of progeny. Mean development time from birth to adult increased with increasing cold stress, ranging from 6.6 ± 0.14 days in the control to 10.3 ± 0.14 days in nymphs exposed to -7.5°C for 6 h. When cooled as 1st-instar nymphs to -7.5°C for 6 h, surviving aphids that developed to the adult stage produced a mean of 4.22 ± 0.26 nymphs/day, with an average reproductive life of 7.91 ± 0.89 days and a mean total fecundity of 32.30 ± 3.51 nymphs/adult in an adult life span of 8.04 ± 0.91 days. Aphids cooled to -7.5°C for 6 h as newly moulted, pre-reproductive adults produced 5.87 ± 0.19 nymphs/day over 5.58 ± 0.45 days, with a mean total fecundity of 31.88 ± 2.40 nymphs/adult in a life span of 5.58 ± 0.45 days. In general, mean daily fecundity, length of reproductive life, total fecundity and adult longevity all increased with less stressful exposures. A control sample produced 7.58 ± 0.14 nymphs/day over 11.90 ± 0.30 days, with a mean total fecundity of 89.36 ± 1.28 nymphs/adult in a life span of 17.44 ± 1.14 days. Approximately 50% of nymphs born on the 1st day of the reproductive life of aphids cooled as 1st-instar larvae or newly moulted adults to -7.5°C for 6 h died within 3 days of birth.