Alate production by aphids on sugar beet: how likely is the evolution of sugar beet-specific biotypes?

Abstract

Summary1. Aphid clones that feed on the same plant species for many generations oftendevelop biotypes specifically adapted to the particular host-plant. Such biotypescan be particularly damaging to crops. In the case of sugar beet Beta vulgaris,which is not available for colonization for parts of the year, aphids must migrateinto and out of the crop each year if host-specific biotypes are to evolve. The likeli-hood of biotypes evolving to be specifically adapted to sugar beet was examinedand the results are discussed in relation to the control of aphids on this crop.2. The frequency and causes of alate production by aphids on sugar beet wereinvestigated by examining natural field populations, manipulated field populationsand laboratory populations. Data from these studies were used in a model that esti-mated the probability of an aphid clone on sugar beet successfully migrating fromthe crop, surviving the winter and migrating back on to the crop the followingyear.3. In 2 years out of 4, no alatoid nymphs of the aphids Myzus persicae andMacrosiphum euphorbiae were produced on naturally infested crops of sugar beet,and negligible numbers were produced in the other 2 years.4. In spring, a much greater proportion of the My. persicae population was alatoidon oilseed rape Brassica napus than on sugar beet. Similarly in laboratory studies,a greater proportion of My. persicae was alatoid on Chinese cabbage Brassica peki-nensis than on sugar beet at the same levels of crowding. The colour of the alatoidnymphs reared on Chinese cabbage indicated that it was a more suitable host thansugar beet and this might account for the greater alate production. Infection ofsugar beet with beet yellows virus did not increase alate production by My. persi-cae.5. A deterministic model showed that the probability of an alate My. persicaemigrating from sugar beet and recolonizing sugar beet the following year would, atbest, be only 1 in 40000.6. As there is negligible transfer of genetic material from year to year, we suggestthat biotypes of My. persicae specifically adapted to sugar beet are unlikely toevolve. As a result, if particular aphicides were only used on sugar beet, resistanceto those aphicides would be unlikely to evolve because any new resistance wouldnot be transmitted from year to year.Key-words: alatoid nymphs, Aphis fabae, BMYV, BYV, host races, Macrosiphumeuphorbiae, Myzus persicae, oilseed rape.Journal of Applied Ecology (2000) 37, 40–51