Flowering margins support natural enemies between cropping seasons

IntroductionPopulations of natural enemies of insect pests are declining owing to agricultural intensification and indiscriminate use of pesticides, and this may be exacerbated in agricultural systems that clear all margin plants after the cropping season for other uses such as fodder. Retaining a diversity of non-crop flowering vegetation outside the cropping season may support more resilient and effective natural pest regulation.MethodsWe tested the potential for non-crop vegetation to support natural enemies in fields across two locations after harvesting the primary crops of lablab and maize.ResultsA total of 54 plant species were recorded across the sites in Kenya with 59% of them being annuals and 41% perennials. There was a significant seasonal variation in plant species richness (ANOVA: F1, 16 = 33. 45; P< 0.0001) and diversity (ANOVA: F1, 16 = 7.20; P = 0.0511). While time since harvesting was a significant factor influencing the overall abundance of natural enemies (ANOVA: F2, 1,133 = 8.11; P< 0.0001), they were generally higher in abundance in locations with margin plants or where a diversity of margin plants was observed.DiscussionThese findings demonstrate that flowering plants in agricultural systems offer refuge and alternative food for natural enemies and potentially other beneficial insects between cropping seasons. The conservation of natural enemies between crops may lead to more effective natural pest regulation early in the following crop, thus reducing reliance on insecticides application

Lablab (Lablab purpureus L.) genotypes and field margin vegetation influence bean aphids and their natural enemies

Dolichos bean (Lablab purpureus L.) is an important food and livestock feed legume that can also enhance soil fertility. However, its production is limited by insect pests, notably the black bean aphid (Aphis fabae). The present field study was conducted to determine the difference in contribution of dolichos genotypes and natural field margin vegetation (FMV) on the abundance and diversity of natural enemies and the damage, incidence and abundance of bean aphids. Eighteen lablab genotypes were planted in the presence or absence of FMV in a randomized complete block design 24 experiment replicated four times. Data on aphid abundance, incidence and severity of damage were collected at four growth stages of the crop. Dolichos genotypes significantly influenced aphid incidence thereby suggesting some level of tolerance to aphid colonization. Findings showed that dolichos genotypes were significant for natural enemies species richness with no statistical difference for abundance and natural enemies species diversity. However, the genotypes did not vary significantly in their influence on numbers of aphid natural enemies. FMV was associated with low bean aphid damage. Overall, the presence or absence of FMV did not influence the number of natural enemies caught on the crop. This concurs with recent work that shows similar numbers of natural enemies with field margin plants but may reflect the reduced number of pest insects. Cropping seasons influenced aphid abundance and damage severity, with the populations developing at early stages of lablab development and decreasing as the crop advanced. This pattern was similar both in presence or absence of FMV. The findings of this study highlight the important contribution of crop genotype together with the presence of field margin species in the regulation of aphids and their natural enemies in lablab

Field margins and botanical insecticides enhance Lablab purpureus yield by reducing aphid and supporting natural enemies

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 early and late vegetative growth stages. Data was 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 to the untreated control. However, the number of natural enemies was 34% higher in botanical insecticide treated plots than in plots treated with the 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 habitat 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