Suitability of clovers (Trifolium species and cultivars) as hosts of spotted clover aphid, a biotype of Therioaphis trifolii (Monell) (Hemiptera : Aphididae)

Abstract

Summary. The performance of the spotted clover aphid, a biotype closely related to the spotted alfalfa aphid Therioaphis trifolii (Monell) f. maculata, was assessed on 18 accessions, all of which were cultivars of clover (Trifolium spp.) commonly grown in improved pastures in Australia. Aphids were reared on excised trifoliate leaves on agar containing a soluble fertiliser. Parameters measured were initial host acceptance by apterous adults, survival of first generation nymphs, incidence of alate adults produced, and the 4-day fecundity of apterous adults. A host suitability index was calculated for each of the cultivars tested. Most of the accessions were readily accepted by spotted clover aphid and nearly all proved to be suitable hosts. Mortality and alate production were generally low and fecundity of F₁ apterae averaged more than 5 offspring per day on all cultivars in the 4-day fecundity study. Spotted clover aphid performed particularly well on 9 of the 10 cultivars of subterranean clover. The white clover cultivar Irrigation was the least suitable host. Spotted clover aphid has the potential to be a serious threat to improved pastures in Australia where clover is a major component.