Dolichos (Lablab Purpureus L.) Genotypes and Field Margin Vegetation Effects on Bean Aphids and Their Natural Enemies

Abstract

Dolichos bean (Lablab purpureus L.) is a drought tolerant multipurpose legume used for food/feed and soil fertility management. Despite these benefits, dolichos remains underutilized and unexploited in terms of area under cultivation and efforts towards its genetic enhancement particularly resistance towards insect pests and diseases.There is need for selection of tolerant/resistant genotypes that can be integrated with other natural pest regulation strategies for the management of insect pests specifically the bean aphid. A field and cage exclusion experiments were conducted at the Agronomy Research and Teaching field of Egerton University, Njoro campus, during the 2019 and 2020 crop growing seasons to determine the effect of dolichos genotypes and field margin vegetation (FMV) on abundance and diversity of natural enemies. The treatments consisted of 18 dolichos genotypes which were planted in the presence or absence of margin plants. The margin plants consisted of four weed species: black jack (Bidens pilosa L.), Mexican marigold (Tagetes minuta L.), goat weed (Ageratum conyzoides L.) and gallant soldier (Galinsoga parviflora Cav.). The treatments were laid out in a randomized complete block design (RCBD) with four replicates. Data collected on aphid abundance, percent incidence and damage severity, natural enemy populations, yield and yield components of dolichos were subjected to analysis of variance using Statistical Analysis System (SAS) version 9.2. Results showed significant seasonal variations in bean aphid infestation levels (P<0.001). Further results showed significant interactive effects between dolichos genotypes and FMV on aphid abundance and percent incidence (P<0.001). The presence of FMV showed, low aphid abundance (1.24) in 2019 cropping season compared to the 2020 (2.59) season. The lowest aphid abundance was observed on genotypes Machakos I (1.76) and Brown Rongai (1.75). Among the natural enemies captured, the most abundant were Tachnid flies (6.19), hoverflies (1.0), parasitic wasps (2.93) and ladybird beetles (1.07).Genotype Echo-Cream had low hoverfly abundance while Machakos-II had high abundance of ladybirds across the two seasons. Genotype Brown - Rongai had the highest yield of 0.97 t/ha while Machakos - I and HA-4 had the lowest yields of 0.19 t/ha in the two seasons. These findings highlight the potential of integrating bean aphid tolerant dolichos genotypes and field margin vegetation in suppressing bean aphid infestation and supporting natural enemies of bean aphids in dolichos production