Overwintering and dispersal of cereal aphids

Hand, Stephen Charles (1982) Overwintering and dispersal of cereal aphids. University of Southampton, Doctoral Thesis.

Abstract

Cereal aphids are a major pest of crops. There are seven important pest species found in Britain- Sitobion avenae F., S. fragariae Wlk., Rhopalosiphum adi L., RL insertum Wlk., R. maidis Fitch, Metorolophium dirhodum Wlk. and M. festucae Theobald. The purpose of the work presented in this thesis was to study the biology of these species from the time they leave cereals in late summer until the time they increase in numbers in the following summer. The main part of the work involved sampling host plants from September to May on a farm in southern England. All the species are able to overwinter anholocyclically on graminaceous plants under some conditions. Thus extensive sampling was carried out on the available graminaceous hosts (i.e. winter cereals, maize, grass crops, wild grasses etc.) to assess their importance during the winter for the different aphid species and to provide information on the effect of weather and other winter environmental factors on the number of aphids. The main sampling method used was the 'D-vac' vacuum insect net; its use necessitated studies on its capture efficiency so that absolute numbers of aphids could be estimated. The effects of some environmental factors on the 'D-vac' capture efficiency were also investigated (in the laboratory). In addition to anholocyclic overwintering, most of the aphidspecies are able to overwinter holocyclically (i.e. with an egg stage). This was examined in depth for one species only M. dirhodum, on its primary host, Rosa app. Intensive sampling of Rosa on the study farm was carried out to estimate its relative importance as a winter host (compared with Gramineae) and to find the preferred rose sites. In order to aid the identification of the aphids collected from Rosa, multivariate statistical methods were used on morphometric data. The use of these methods for separating elate morphs of M. dirhodum was also examined. The importance of winter in the development of pest outbreaks was examined by sampling the study area in summer and by analysing published long-term records of aphid numbers in relation to preceding winter weather. Aspects of the production of sexual and elate morphs of the monoecious cereal aphids, S. avenge and M. festucae, and the hatching requirements of S. avenae eggs were examined in the laboratory.The problems of studying overwintering, the gaps in our knowledge and the potential uses of the data were discussed.

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