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Encouraging Beneficial Insects

Everybody is familiar with ladybugs and lacewings as voracious, pest consuming beneficial insects. But fewer are familiar with how natural enemies such as hover flies, ground beetles, and even yellow jacket wasps contribute to a healthy integrated pest management (IPM) plan by reducing pest numbers. Through augmentation, conservation, and introduction of natural enemies, producers can not only increase their populations in their fields, but also benefit from a healthier, better producing crop.
 
According to the classic “Natural Enemies Handbook” (ISBN 978-0-520-21801-7) by Flint and Dreistadt, use of beneficial insects or natural enemy populations is based on three basic principles in agriculture today; conservation and enhancement, augmentation, and classical biological control or importation. All three of these relate to the principles of bio-controls which were introduced previously (Predation, Parasitism, Herbivory, Antibiosis, and Competition), but vary in their use in the industry.
 
Greenhouse producers are perhaps most familiar with the concept of augmentation where a crop is either inoculated with a natural enemy or inundated with it. In an inoculation situation, beneficial insects that were reared in a lab or collected in a field are introduced to an area such as a greenhouse or field. Typically the goal of these insects is to breed and increase in population over the course of the program, (hopefully) resulting in control throughout the season. Most commonly, inoculation is used after an event which has decimated the native population such as a pesticide application, a weather event or may be done in a space where natural enemies are typically absent (i.e. a greenhouse situation).
 
In a similar vein, the inundative approach to augmentation introduces a species of beneficial insect but uses it to treat a ‘hot spot’ or problem area, effectively overwhelming the pest in numbers. This population is often short lived and while it may maintain a base level, natural enemy populations will commonly drop alongside the pest population as it can no longer sustain it. While both of these techniques are commonly used in greenhouse situations, they are less applicable to field growers, as most beneficial insects used in this way aren’t typically capable of overwintering. Furthermore, they can be an expensive prospect for field growers given how mobile many of these controls tend to be.
 
Classical biological control or importation generally involves looking at a pest’s native range, finding a natural enemy of it there and importing it into its adopted range. This type of biological control has historically been controversial as it often involves importing a foreign species which can itself potentially become a pest. Nowadays, this research is often undertaken at a federal level with a substantial amount of due diligence and consideration. However, successful Canadian examples do exist in the control of St. John’s wort and leafy spurge. Given how risky this process can be, it is more commonly reserved for invasive species which present a substantial threat to native plants and ecosystems, making it out of reach for the average grower.
 
The final method, conservation and enhancement, is where most field growers will see real benefit in their operation. Most fields generally have much larger populations of beneficial insects than pests; however these can be substantially reduced in the process of killing pests. In some cases this can actually exacerbate the problem by removing barriers to another pest becoming a problem, resulting in a secondary wave.
 
Many sources will often treat natural enemies as “livestock”; just as a cow needs water, feed, and shelter, so do the beneficial insects in a producers field. So how best to keep your livestock happy? One of the easiest ways is to avoid the use of pesticides that may harm them. Using selective pesticides, selective applications (i.e. applying only to areas of concern) or timing applications to a time when they’re not active such as early morning can help mitigate losses of beneficial insects. Similarly, minimizing cultural practices like soil disturbance, burning, and timing irrigation better can also all go a long ways to making a field more hospitable to natural enemies.
 
Feed and water for these beneficial “livestock” can come in many forms; small pools of standing water, other insects, and pollen and nectar from a diversity of plants. Shelter for natural enemies can often be found in areas with increased plant diversity such as headlands and surrounding trees and shrubs. Similarly, for soil dwelling insects, excessive heat can interrupt lifecycles and decrease activity. Cover crops can not only work to alleviate this heat but will ensure further plant diversity and increased diversity amongst beneficial controls. 
 
As with most topics, knowledge is power. The more that a producer knows about their native natural enemies, the better they can manipulate the environment to make it more inviting for these ravenous little beasts. By incorporating a few new techniques into their operation, growers can ensure happy, healthy ‘livestock’ and a crop yield that reflects it.
 
Source : Agriculture and Forestry

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