Scope for non-crop plants to promote conservation biological control of crop pests and serve as sources of botanical insecticides

Abstract

Besides providing food and shelter to natural enemies of crop pests, plants used in conservation biological control interventions potentially provide additional ecosystem services including providing botanical insecticides. Here we concurrently tested the strength of these two services from six non-crop plants in managing cabbage pests in Ghana over three successive field seasons. Crop margin plantings of Ageratum conyzoides, Tridax procumbens, Crotalaria juncea, Cymbopogon citratus, Lantana camara and Talinum triangulare were compared with a bare earth control in a three-way split plot design such that the crop in each plot was sprayed with either a 10% (w/v) aqueous extract from the border plant species, a negative control (water) and a positive control (emamectin benzoate 'Attack' insecticide). Pests were significantly less numerous in all unsprayed treatments with non-crop plant margins and in corresponding sprayed treatments (with botanical or synthetic insecticide positive control) while treatments with bare earth margin or sprayed with water (negative controls) had the highest pest densities. Numbers of predators were significantly depressed by synthetic insecticide but higher in other treatments whether unsprayed or sprayed with botanical insecticide. We conclude that some plant species have utility in both conservation biological control and as source of botanical insecticides that are relatively benign to natural enemies. In this crop system, however, the additional cost associated with using botanical insecticides was not justified by greater levels of pest suppression than achieved from border plants alone. Insect pest attack causes huge crop losses 1 affecting the potential availability of food for over one billion people 2 , and threatening global food security 3. Effective pest management is critical to meeting global food demands 4-6 and synthetic insecticides have been the principal tool in the past six decades 7,8. Even with the introduction of newer and relatively safer insecticides 8 and increased application per unit area and time 9 , crop loss resulting from insect damage has doubled in the past four decades 1,10,11. Indiscriminate and excessive application has led to the elimination of important organisms in the agroecosystem that support crop production 12,13. This is especially prevalent in developing countries including Ghana where farmers and the environment are exposed to high levels of synthetic insecticides, including active ingredients that have been banned in developed nations due to high toxicity and persistence 14. Inadequate provision of important ecosystem services including natural enemy-mediated pest control reinforces reliance on hazardous inputs such as insecticides and threatens agricultural sustainability 15,16. Conservation biological control based on habitat manipulation has been proposed as a sustainable alternative to synthetic insecticides 17. Habitat manipulation involves intentionally establishing plant species at the farm scale or landscape scale to provide conduc...

Tracking research trends on the effects of vegetative strips within agricultural landscapes: A systematic map update

“…For example, studies investigating crop pollination, pest regulation, and climate regulation have increased, relative to other ecosystem services. This may have occurred for several reasons, such as the increasing recognition in the global decline of terrestrial insects (Geppert et al 2020;van Klink et al 2020), recognition of the threats insects are likely to face due to climate change (Vasiliev & Greenwood 2021), and a shift away from harmful pesticide chemicals toward biological pest control (Albrecht et al 2020;Amoabeng et al 2020). Additionally, there is increasing awareness that climate change is likely to impact agricultural activities (Karki, Burton & Mackey 2019;Ng'ombe, Tembo & Masasi 2020) and a corresponding recognition that vegetative strips have the capacity to reduce water consumption by crops and provide favorable microclimatic conditions for agriculture (Thevs et al 2019;Chenet al 2020).…”

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

“…In contrast to persistent synthetic insecticides, the active components in botanical insecticides degrade rapidly in nature often owing to their instability especially in UV light, and consequently, they have lower impacts on predators and parasitoids of pests (Stevenson et al, 2017). However, combining field margins and botanical insecticides requires careful assessment of their individual and combined effects on pests and natural enemies, and the overall impact on crop yield (Amoabeng et al, 2020).…”

“…Integrated Pest Management (IPM) draws on the combination of different pest control methods to maintain pest populations below economically important thresholds and minimise non‐target effects (Amoabeng et al, 2020). Bean aphids can be controlled using natural enemies at levels that mitigate against severe losses without reliance on chemical pesticides (Bianchi et al, 2006; Bianchi & Wäckers, 2008; Rand et al, 2006).…”

Predators and the management of some agricultural pests in Ecuador

“…Dentro de la entomofauna benéfica, los depredadores constituyen importantes agentes de control biológico que se caracterizan por consumir muchas presas durante toda su vida (van den Bosch et al, 1982). En el mundo se han documentado los casos acerca de la acción de los depredadores en agricultura, y aunque algunos investigadores refieren resultados heterogéneos acerca de la efectividad de su acción (Karp et al, 2018) estos enemigos naturales constituyen una parte importante del control biológico de plagas (Amoabeng et al, 2020;Castillo Carrillo, 2020; van Driesche et al, 2020). Por esta razón, es importante, revisar para Ecuador la magnitud y efectividad del uso de estos enemigos naturales, lo que constituye el objetivo más importante de este trabajo.…”