Aphids infesting potato in Kenya.

Abstract

Abstract Aphid-transmitted viruses probably cause greater economic loss in potato production than all other insect-related damage. Some 40 virus species are known to infect potato, and of these 13 are aphid transmitted. Monitoring of aphid populations in potato fields is therefore essential to determine areas with low aphid occurrence suitable for seed potato production and the right time for haulm destruction. While plenty of information on such areas is available in traditional seed-potato-producing countries of America and Europe, there is none available for Kenya. The current study determined the best locations for seed potato multiplication by monitoring aphids (from May 2009 to March 2010) in major potato-producing areas of Kenya. Two methods, yellow water traps (YWTs) and leaf-aphid counts, were utilized. Ten aphid species, Aphis gossypii (Glover), Aphis fabae (Scopoli), Aulacorthum solani (Kaltenbach), Acyrthosiphon pisum (Koch), Brevicoryne brassicae L., Cavariella aegopodii (Scopoli), Macrosiphum euphorbiae (Thomas), Myzus persicae (Sulzer), Myzus ascalonicus (Doncaster) and Rhopalosiphum maidis (Fitch) were caught in YWTs while four aphid species, A. fabae, A. gossypii, M. persicae and M. euphorbiae were also found colonizing potato leaves. The populations of the aphid species varied significantly, R. maidis had the greatest numbers, followed by B. brassicae, A. gossypii, M. euphorbiae, M. persicae and A. fabae in this order while A. solani was the least abundant. The populations of A. fabae, A. solani, C. aegopodii and M. ascalonicus did not vary between seasons and sites but A. gossypii, A. pisum, B. brassicae, M. euphorbiae, M. persicae and R. maidis populations varied significantly between the five sites, and between the three seasons. Although aphid numbers recorded at all sites were above the threshold for virus transmission, not all the species caught were efficient virus vectors. In conclusion, Njabini consistently had low aphid numbers and may be the site most suitable for seed potato multiplication.