Diversity and infestation levels of arthropod pests attacking dolichos lablab (l.), grown in Meru central and Yatta Sub-counties, Kenya

Abstract

Dolichos lablab (L.) is one of the many crop species that are neglected and undercultivated in Kenya. This crop is different from the other grain legume crops due to the fact that its economic potential has been poorly exploited. These economic values of D. lablab may not be realized, due to; poor planting materials, limited genetic diversity, poor agronomic practices and arthropod pests and disease. Arthropod pests are probably the main factors limiting D .lablab production in Kenya. However, there is dearth of information on arthropod pests attacking D. lablab in Kenya. This study therefore, aimed at assesing the diversity and infestation levels of key arthropod pests infesting D. lablab. It was conducted Yatta and Meru Central sub-counties. In each sub-county, four irrigated and four rainfed D. lablab farms were randomly selected for sampling of arthropod pests. Sampling was done by using five 0.09m2 (30cm by 30cm) quadrat which was randomly placed in five stations per sampling session. Arthropod pest species composition, diversity, infestation levels were analysed from each sub-county and compared between wet and dry seasons, irrigated and rain fed conditions, phenological stages of the crop and intercropping patterns. Results revealed that D. lablab was infestated by thirteen insect pest species and mites, dominated by Megalurothrips sjostedti and Clavigral/a spp. in the both sub-counties; however diversity index was 4.5. The infestation levels of arthropod pests varied significantly between sites, seasons and irrigated and rain fed systems. The diversity index was 3.8 in both Meru and yatta in dry and wet seasons. Mean numbers of Eggs and larvae of M testulalis were significantly higher (t-test) in Yatta (1.9 ± 0.3 and 5.9 ± 0.6) than Meru (0.9 ± 0.2 and 2.4 ± 0.4); the rest of the species did not vary between sites. M sjostedti infestation levels in dry season (152.2 ± 20.0) was significantly higher (t-test) than wet season (73.3 ± 13.3) in Meru. Clavigralla spp. infestation level of nymphs and adults was significantly (t - test) higher in wet season (33.3 ± 7.8) than ill dry season (6.7 ± 2.0) in Yatta. In Meru central infestation rates oi Lmomyza spp., Bemisia spp. and Aphis spp. in wet season had medians of2.0, 2.0 and 1.0 respectively and were significantly (Mann-whitney test) higher than dry season. In wet season infestation level of larvae of H amigera was significantly higher in rain fed D. lablab (20.7 ± 1.4) than irrigated D. lablab (6.0 ± 1.2) in Meru. M sjostedti infestation level in irrigated (1762 ± 11.0) was significantly (ANOVA) higher than rain fed (117.1 ± 3.0) in Meru. Most of the arthropod pests started infestation at the vegetative and flower budding and levels increased in.flowering and podding stages. In dry season, Bemisia spp. and Liriomyza spp. infestation levels were significantly (ANOVA) higher in irrigated D. lablab grown alone compared to the rest of the cropping patterns in both Meru and Yatta. M sjostedti infestation level in irrigated D. lablab grown with bananas (176.2 ± 11.1) was significantly (ANOVA) higher than rest of the intercropping patterns in dry season. Clavigralla spp. nymphs and adults infestation level in rain fed D. lablab grown with bananas (54.2 ± 6.1) was significantly (ANOVA) higher the rest of the intercropping patterns in wet season. From the study it can be concluded that location, seasonality, irrigation and rain fed conditions and phenology of the crop significantly affects, infestation level of arthropod pests species, though not all species are affected by these factors.The results of this study provides basic information on arthropod pests attacking D. lablab during wet and dry seasons, in irrigated (vegetable type) and rain fed (grain type), at different phenological stages and different cropping patterns. The information obtained will form an important basis for further research work in trying to look for appropriate controlmeasures of these arthropod pests of D. lablab