The development rate of Metopolophium dirhodum (Walker) (Hemiptera: Aphididae) on winter wheat

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Abstract
Intensive monitoring of uncaged summer populations of Metopolophium dirhodum (Wlk.) (alienicolae) on winter wheat in southern England was carried out, mainly in 1979. Estimates for rates of development and reproduction are presented for both apterous and alate morphs. Relative nymphal instar lengths were calculated as percentages of the total juvenile period (instars I–IV inclusive), at a given mean temperature. The durations of the first three nymphal instars were uniform, but longer was spent in instars IV-apterous (21%) and IV-alatiform (45%) than in previous ones. Development rates are shown, firstly as cumulative summations of regression lines for individual instars, and secondly as a single regression for the whole period (I to IV inclusive), plotted separately against corresponding mean temperatures. A method of calculating the development threshold was devised that yielded an estimate of about 5°C for both morphs. Average and maximum daily rates of deposition (larviposition) are given for both morphs and, for apterae, results on the effects on this of leaf, date, temperature and aggregation are presented and discussed. Comparisons are made between this field study, and previous ones using M. dirhodum under constant temperature conditions in the laboratory. Development rates appeared to be similar under both constant and fluctuating temperatures, although slower in the field at low temperatures (10 or 11°C). Reproductive rates under the field conditions of this study appeared to be higher (on a daily rate basis) than those of previous studies, both in the laboratory (at constant temperature) and in the field. Reproduction in the field by apterae is considered to be concentrated over a shorter span of adult life than in the laboratory.