The winter development, reproduction and lifespan of viviparae of Sitobion avenae (F.) (Hemiptera: Aphididae) on wheat in England

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Abstract
Viviparae of Sitobion avenae (F.) in clip-cages on winter wheat in field plots in southern England were monitored throughout the 1980–81 winter to determine characteristics of development, reproduction and lifespan under winter conditions. Rate-temperature relationships for development and reproduction were well described by straight lines when temperatures were measured above 3°C. A simple thermal-time scale could therefore be used for both processes. The parental morph and the time of year modified thermal-time requirements for the production of an adult's first 20 nymphs but did not affect those for development. For both alatae and apterae, nymph production per day-degree was greater than at higher temperatures and the relationship between reproductive rate and age was different. The minimum temperature experienced by the aphids was −7°C; survival was good, with little low temperature mortality. Total fecundity of apterae was usually greater than at higher temperatures, though some apterae and alatae that were deposited in October had low fecundity, possibly because they were insufficiently acclimatized at the onset of cold winter weather. Overwintering alatae had lower development rates, reproductive rates and total fecundity than apterae and did not survive as long, but were restless as young adults and appeared ready to migrate. Oviparae were produced from late September to mid-October but not after this, suggesting that the clone used could ‘switch off’ sexual morph production in winter.