Browsing by Author "Mulwa, Richard"

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    Field margins and botanical insecticides enhance Lablab purpureus yield by reducing aphid pests and supporting natural enemies
    (John Wiley and Sons Inc, 2022-05-20) Ochieng, Lawrence; Ogendo, Joshua; Bett, Philip; Nyaanga, Jane; Cheruiyot, Erick; Mulwa, Richard; Arnold, Sarah; Belmain, Steven; Stevenson, Philip
    Botanical insecticides offer an environmentally benign insect pest management option for field crops with reduced impacts on natural enemies of pests and pollinators while botanically rich field margins can augment their abundance. Here, we evaluated the non-target effects on natural enemies and pest control efficacy on bean aphids in Lablab of three neem- and pyrethrum-based botanical insecticides (Pyerin75EC®, Nimbecidine® and Pyeneem 20EC®) and determine the influence of florally rich field margin vegetation on the recovery of beneficial insects after treatment. The botanical insecticides were applied at the early and late vegetative growth stages. Data were collected on aphids (abundance, damage severity and percent incidence) and natural enemy (abundance) both at pre-spraying and post-spraying alongside Lablab bean yield. The efficacy of botanical insecticides was similar to a synthetic pesticide control and reduced aphid abundance by 88% compared with the untreated control. However, the number of natural enemies was 34% higher in botanical insecticide-treated plots than in plots treated with synthetic insecticide indicating that plant-based treatments were less harmful to beneficial insects. The presence of field margin vegetation increased further the number of parasitic wasps and tachinid flies by 16% and 20%, respectively. This indicated that non-crop habitats can enhance recovery in beneficial insect populations and that botanical insecticides integrate effectively with conservation biological control strategies. Higher grain yields of 2.55–3.04 and 2.95–3.23 t/ha were recorded for both botanical insecticide and synthetic insecticide in the presence of florally enhanced field margins in consecutive cropping seasons. Overall, these data demonstrated that commercial botanical insecticides together with florally rich field margins offer an integrated, environmentally benign and sustainable alternative to synthetic insecticides for insect pest management and increased productivity of the orphan crop legume, Lablab.
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    Intercropping and diverse field margin vegetation suppress bean aphid (Homoptera: Aphididae) infestation in dolichos (Lablab purpureus L.)
    (Polska Akademia Nauk, 2021-10-12) Mwani, Christine; Nyaanga, Jane; Cheruiyot, Erick; Ogendo, Joshua; Bett, Philip; Mulwa, Richard; Stevenson, Philip; Arnold, Sarah; Belmain, Steven
    Dolichos (Lablab purpureus L.) is a drought tolerant legume used as food/feed and improvement of soil fertility. The production of dolichos in Kenya, Nakuru County is however limited by insect pests like bean aphids, pod borers and whiteflies. Field studies were conducted to determine the effect of cropping systems (dolichos monocrop and maize-dolichos intercrop) and field margin vegetation on bean aphids and their natural enemies. The experiment was conducted in Njoro (high field margin vegetation) and Rongai (low field margin vegetation) during May–December 2019 and March−November 2020 cropping seasons. Bean aphid percent incidence, severity of damage and abundance was assessed at seedling, early vegetative, late vegetative and flowering dolichos growth stages. The populations of natural enemies in the plots and field margin vegetation were monitored using pan traps and sweep nets. Species diversity and composition of the field margin vegetation was determined using a quadrat. Results showed that location and cropping system had significant effects on bean aphid infestations. A high bean aphid incidence (38.13%) was observed in Njoro compared to Rongai (31.10%). Dolichos monocrop had significantly higher bean aphid infestation (51.63%) than the maize-dolichos intercrop system (24.62%). A highly diverse Shannon-weaver index was observed in Rongai (1.90) compared to Njoro (1.67). Dolichos monocrop had a more diverse Shannon-weaver index (1.8) than the maizedolichos intercrop system (1.7). Rongai had the most abundant annual and perennial field margin vegetation species. The field margin species richness and diversity were higher in Rongai (81%) than in Njoro (54%). The findings of this study have demonstrated that a maize-dolichos intercrop in Rongai can reduce bean aphid damage in dolichos.