The ecology of Aphis craccivora Koch and subterranean clover stunt virus. I. The phenology of aphid populations and the epidemiology of virus in pastures in south-east Australia.
Abstract
The following is based largely on the authors' summary. The ecology of Aphis craccivora Koch and subterranean-clover stunt virus [cf. RAE A 58 646] was examined in New South Wales in 1969 in five pastures sown with different combinations of leguminous plants. During the autumn, alates of A. craccivora infest newly germinated pastures throughout south-eastern Australia. This aphid is extremely cold-susceptible and does not generally survive the winter in most areas. A second infestation of the pastures by alates may occur in spring [cf. 47 474]. Ecological data indicating that the aphid has an exceptionally high potential for migration are given. In autumn, alates introduced the subterranean-clover stunt virus into the pastures. Peak numbers of infected plants in pastures of subterranean clover (Trifolium subterraneum) occurred in mid-winter after the decline of the aphid population. However, virus symptoms were not observed on white clover (T. repens), lucerne or other leguminous pasture plants that were growing in these pastures, nor in pastures of medick. Field studies indicated that A. craccivora exhibits distinct patterns of food-plant selection in pastures containing several leguminous species. Laboratory studies showed that some of these plants, such as lucerne, are unsuitable as food-plants, while others, such as white clover, are suitable though they are not attacked in nature. Of the leguminous plants observed in the field, common burr medick (Medicago polymorpha vulgaris) was both highly suitable and preferred. Data on the relative susceptibility of some preferred pasture species to infection by the subterranean-clover stunt virus are given. These observations, with others on initial infestation rates and pasture infection rates, as well as observations on the growth form of some species in nature are used as the basis for hypotheses concerning the epidemiology of the virus in Australia. These postulate that most species of Medicago are probably not very important reservoirs for the virus; that species such as white clover are probably not important either, because they are not preferred food-plants of the aphid; and that subterranean clover is probably the most important host for the virus in nature.