by Thomas Grandperrin
Published on February 21, 2019
This article was initially published on Freshfruitportal.com.
In two previous articles, we presented classical biological control, the practice of finding a pest’s natural enemy in its original ecosystem and bringing it back to feast upon your pest populations, and augmentative biological control, the practice of bolstering local beneficial populations by adding more of an existing species to the dinner party. The last type of biocontrol we will present is conservation biological control (CBC), which can be summarized as the set of practices that aim to ensure that natural enemies have a suitable habitat capable of supporting their populations at required levels. This includes placing new habitats such as specific cover crop types into the environment as well as preventing chemical applications from making existing habitats unsuitable.
Two primary drivers for the need to implement conservation biocontrol are the use of broad range synthetic pesticides, which often have the side effect of reducing the indigenous population of natural enemies, and the simplification of plant ecosystems (monocropping) which reduces the habitat and the food of some natural enemies. Conservation control can be implemented as a “stand-alone” management technique or as a complementary technique of augmentative biocontrol beneficials release within a comprehensive integrated pest management plan. It generally consists of modifying field management practices and/or the ecosystem itself to reestablish or increase the development of naturally occurring predators, parasitoids and pathogens but also of pollinators.
Conservation control plans can contain a variety of conservation measures, including plant and habitat diversiﬁcation, reducing cropping intensity, and increasing landscape complexity, which should result in increased density and variety of beneficials. Some examples include inter-row cover planting, seeding flowers that bring additional resources to beneficials, planting hedgerows, building physical refugees for the hibernation/overwintering of the natural enemies, seeding trap plants that attract pests, and release of alternative prey for beneficials to feed upon when pest populations are low. Indeed, it is important to allow natural enemies access to diverse food sources. That way, when pest populations dip below levels sufficient to serve as a sole food source, beneficials such as predatory mites, parasitoid wasps, and green lacewings, that also feed on pollen and nectar in addition to pest populations, can survive and still be present in the field to control future pest outbreaks.
Conservation control techniques are usually quite local specific, which is one of the reasons why they are not widely documented. Among the popular examples, there is the case of Anagrus erythroneura, the parasitoid that efficiently controls the eggs of the western grape leafhopper, a pest that affects grape yield and quality. But because the leafhoppers overwinter at the adult stage, the parasitoid population declines quickly without egg hosts. As part of a CBC strategy, researchers and viticulturists have successfully planted alternative host plants adjacent to the vineyard as an overwintering site for the parasitoid. A regional variation in pest-parasitoid relationships was found, highlighting the need to adapt CBC techniques to local environments. To provide a few examples, in Oregon and Washington, Anagrus was mainly found on blackberry or rose bushes, while in California, mint, catnip, and California lilac are better alternative hosts capable of sustaining populations until the leafhoppers re-emerge on the vines the following season.
In Denmark, buckwheat flowering strips (a rich pollen source) are used to enhance Copidosoma aretas, a parasitoid of the strawberry tortrix moth (Acleris comariana) a major pest in Danish strawberry production. This plant is also used as a cover crop in some California vineyards to attract some beneficials such as predatory wasps, minute pirate bugs and hoverflies.
In perennial crops such as fruit orchards, natural enemies have a better chance of surviving from one season to the next since their habitats are less likely to be destroyed during harvest. But conservation biological control has also shown to add great value in annual crops and has been implemented in various types of production, from agroecology to organic or conventional farming.
Do you have any experience with conservation biological control? Share your story with us and fellow growers in the comments!
If this series on biological control has encouraged you to further explore how you can implement some of the techniques in your own integrated pest management plan, we’d love to hear about it. We’d also love to hear your suggestions for future articles.
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