INSECT DIVERSITY AND THEIR SUITABLE MANAGEMENT ON AFRICAN INDIGENOUS VEGETABLES IN WESTERN KENYA

Abstract

Insect pests, especially aphids (Hemiptera) and flea beetles (Coleoptera), have been documented to lower the yield and quality of common African indigenous vegetables (AIVs) in western Kenya. Their persistence and severity is one of the major reasons for low yields in this region. This study was therefore done to establish the insect pests of AIVs in western Kenya and evaluated a selection of aphid pest management intervention technologies. A field survey was conducted in Homa Bay, Siaya, Kisumu, Busia, Kakamega, Uasin Gishu and Kisii counties where amaranth (Amaranthus sp), spider plant (Cleome gynandra) and nightshade (Solanum nigrum) are commonly produced and consumed. This was to develop an inventory of the AIV common insect pests. The counties were sub-divided into agro-ecological zones. From the survey, 84.6% of total insect species collected were pests. Hemipterans were most numerous, while coleopterans were most diverse. AIV insect species diversity was higher in spider plant, then amaranth and least in nightshade. Aphids were the most important common pest with Aphis fabae and Myzus persicae found on all three AIV among the six aphid species identified. The highest insect diversity was found in the lower highland agro-ecological zone where annual polyculture is practiced, while the lowest diversity was found in lower midland agro-ecological zone where perennial monoculture (sugar-cane farming) is practiced. Additionally, a three replicate split-plot in RCBD experiment was laid in Mwamba Lugari sub-county during rainy and dry seasons to evaluate a selection of aphid pest management technologies. They included traditional wood ash, botanical neem (azadirachtin 0.03% ai) and synthetic chemical Karate (lambda-cyhalothrin ai) on amaranth (Amaranthus sp) and nightshade (Solanum nigrum). Aphid density and yields data was subjected to analysis using SAS 9.4 and means separated by Turkey-Kramer’s test at 95% confidence level. In both seasons, amaranth and nightshade treated with plain water (control) had significantly (p<0.05) greater aphid densities compared to all other pest management strategies (ash, neem, Karate). Yields of both amaranth and nightshade from dry and wet season were significantly (p<0.05) higher on plots treated with Karate and least on plots treated with plain water. Generally across all seasons and AIV varieties, aphid density was lower in AIVs treated with Karate followed by neem then ash and finally plain water (control). Aphid pressure (density) influences overall yields (higher aphid pressure leads to lower yields). AIV farmers should monitor insect pest densities before treatment application and consider using synthetic pesticides when pest densities are high in order to minimize losses.