OCCURRENCE AND ABUNDANCE OF INSECT PESTS ON AFRICAN INDIGENOUS VEGETABLE VARIETIES UNDER DIFFERENT FERTILIZER TREATMENTS AND SEASONS IN KITALE, KENYA

Abstract

African indigenous vegetables (AIVs) once wild are now among the plants domesticated and are increasingly popular in peoples’ diet. Due to this, they have commercial potential and farmers use fertilizers and improved varieties to enhance their productivity all year round (both wet and dry seasons). Insect pests could be a major constraint to AIVs productivity yet little has been documented about them. It is therefore important to study how improved varieties, fertilizer application and seasonal changes affect the behavior of insect pests so that the best intervention strategies to deal with potential AIV insect pests can be identified. This research aimed at improving the productivity of AIVs by looking at how cultivar and fertilizer affects the occurrence and abundance of insect pests during the rainy and dry seasons. At KALRO- Kitale, three varieties of each of the three AIVs (amaranth, nightshade and spider plant) were planted under three different fertilizer treatments (manure, mavuno and no fertilizer) in a split plot field experiment. The insects that occurred were noted on 5 plants in each plot and their numbers recorded. The data was analyzed using SAS 9.4 and the means with significant differences separated using Tukey’s test at 95% (P<.05). The diversity of insect pests associated with the AIVs included an array of hemipterans, coleopterans, dipterans and lepidopterans commonly found on leafy vegetables. Beetles and Bagrada bugs were common on spiderplants, while stink bugs and soldier beetles were only associated with Amaranth. Leafminers were associated with Nightshade and Amaranth. It was also evident that all pests with the exception of cotton strainers and soldier beetles, which were only observed during the rainy season, were common during both the rainy and the dry seasons. Aphids numbers were the highest recorded on all the AIVs during both seasons although with lower densities during the dry season, particularly on spiderplant. Fertilizer application did not significantly (P<0.05) affect the abundance of pests on Nightshade varieties. However, there was a significant (P<0.05) effect of fertilizer application on the abundance of insect pests on Amaranth and Spiderplant varieties. The abundance of aphids differed significantly among amaranth and nightshade varieties. In order to develop the best pest management strategy, it is vital to take into consideration the crop’s ecosystem and the seasonal changes.