Problems Inherent to Augmentation of Natural Enemies in Open Agriculture

Abstract

Augmentation biological control has successfully replaced a lot of insecticide use in 'closed system' agriculture (e.g., greenhouses). The profitable commercialization of biocontrol agents in greenhouses has created an incentive to expand markets for mass-reared beneficial insects into open agricultural systems, often without sufficient scientific justification. However, the semi-contained nature of greenhouse culture is often critical to the success of augmentation and can serve to mask potential pitfalls and intrinsic limitations of this approach in open systems. Factors contributing to greenhouse successes include the reduced biological diversity of contained agroecosystems, the prevention of agent dispersal, the ability to maintain environmental conditions within a range favorable for the agent, the exclusion of competitors and natural enemies of the agent that might otherwise diminish its efficacy, and the absence of alternative prey/hosts that could divert predation/parasitism from the target pest. There are also problems arising from collection of source material from locally adapted populations, and the inadvertent imposition of artificial selection in the course of laboratory rearing. Besides highlighting these pitfalls, this paper aims to encourage more consideration of conservation approaches prior to investment in augmentation programs which entice farmers into perpetual cycles of 'rear and release.' I argue that although augmentation can benefit agriculture whenever it replaces pesticide applications, it does not constitute an ecologically sustainable solution because it requires continued inputs, and it can distract research attention away from more sustainable objectives. Sustainable biological control is best achieved through modifications to cultural practices that increasingly 'naturalize' agroecosystems, thus facilitating the natural recruitment and persistence of beneficial arthropod fauna, combined with habitat management geared to increasing overall plant and arthropod diversity in the agroecosystem.

The parasitoid Trichogrammatoidea armigera Nagaraja (Hymenoptera: Trichogrammatidae) is a potential candidate for biological control of the millet head miner Heliocheilus albipunctella (de Joannis) (Lepidoptera: Noctuidae) in the Sahel

“…However, compared to the parasitoid H. hebetor augmentative program, the challenge with T. armigera will be its dispersal in pearl millet fields. As suggested by Michaud (2018), augmentative releases in open environments can be challenging. This could even be more complicated because trichogrammatid parasitoids usually disperse only a few meters from release points (Bueno et al, 2012;Gardner et al, 2012).…”

Brazilian Legislation Leaning Towards Fast Registration of Biological Control Agents to Benefit Organic Agriculture

“…Therefore, new approaches to the problem are needed. As phytophagous insects have evolved for millions of years with their natural enemies, the logical approach is to invest in using natural enemies of pests by addressing their ecological importance and usage in agriculture (Michaud 2018). A viable route to accomplish this, as well as compatible food production with biodiversity conservation, provisioning of ecosystem services, and human health, is the promotion of agroecology (UN 2017).…”

“…Among them are those problems and challenges also common to organic agriculture; these include pest monitoring, technology transfer, quality control of natural enemies (which demands specific guidelines), logistic of storage and transport, and release technology. We would also add that local natural enemy population differentiation is a bottleneck because the differentiation in the efficiency of natural enemies can vary within regions (Michaud 2018), especially in a country with continental dimensions, such as Brazil. Most likely, as augmentative biological control and products became more available in the country, this scenario is expected to change because more biological control practitioners will fill these gaps.…”

Using life stage‐structured matrix models to determine natural enemy:pest release ratios for augmentative biological control

“…The idea of employing ABC commercially in greenhouses was first put forth in 1926 by Speyer, a British entomologist who realized that the parasitoid Encarsia formosa Gahan could provide a satisfactory control of whiteflies Trialeurodes vaporariorum Westwood (Speyer, ). Although ABC has a longer history of being deployed in field crops (van Lenteren & Woets, ), its likelihood of success is considered higher when used in contained environments such as greenhouses (Michaud, ). Some factors that may contribute to the increased success of ABC in greenhouses include the prevention of natural enemy dispersal, the possibility of maintaining more favourable environmental conditions for natural enemies, the exclusion of competitors and intraguild predators, and the absence of alternative prey/hosts that could otherwise divert the natural enemy's attack from the target pest (Michaud, ).…”

“…Although ABC has a longer history of being deployed in field crops (van Lenteren & Woets, ), its likelihood of success is considered higher when used in contained environments such as greenhouses (Michaud, ). Some factors that may contribute to the increased success of ABC in greenhouses include the prevention of natural enemy dispersal, the possibility of maintaining more favourable environmental conditions for natural enemies, the exclusion of competitors and intraguild predators, and the absence of alternative prey/hosts that could otherwise divert the natural enemy's attack from the target pest (Michaud, ). It is therefore reasonable to expect that the simplified greenhouse environment may also facilitate, at least in terms of research, the prediction of a pest control outcome upon any type of natural enemy manipulation.…”