Natural Control Methods

Excerpt from Chapter 2, Gardener's Handbook

Table of Contents

1. Natural Control Methods
2. Promoting Beneficial Insects
   • Table 3 - Common Predators and Their Prey
   • Table 4 - Common Parositoids and Their Hosts
   • Table 5 - Parositoids and Predators that Can Be Purchased
3. Related Links

Natural Control Methods

Many insect pests have natural enemies that provide some control. They are classified as either predators (Table 3) or parasitoids (Table 4). Predators feed on smaller or weaker insects while parasitoids live in or on the bodies of their hosts. In addition, there are numerous bacteria, fungi and viruses that help reduce pest populations.

Many predators and parasitoids are closely related to the pest species and will look very similar. You would be wise, therefore, to get to know the more common beneficial species in the garden. To determine whether an insect is the problem or part of the solution, look for feeding injury on the plant. Watch the insect to see if it is feeding on the plant or on another insect. Look at its movements; fast-moving insects are generally predators as they need to catch their prey.

Promoting Beneficial Insects

To promote beneficial insects and other organisms in your garden, plant a variety of flowering plants which provide pollen and nectar for adult insects such as parasitic wasps and flies. You must also be careful in your use of pesticides in the garden, as some beneficial insects are killed by smaller doses of insecticides than are required to kill harmful insects. You must also take care to avoid pesticide drift to neighbouring plants which may harbour beneficial insects.

There are several additional tactics that you can use, but there are risks. Mulch between rows of plants provides a natural refuge for predators such as ground beetles, but may also encourage slugs and sowbugs. Native predators such as ladybird beetles can be introduced, but if you buy beetles (Hippodamia convergens) imported from the U.S. you will realize little benefit. These beetles are collected while wintering in the mountains of California. Upon release here, they fly away before settling down to feed again. Few if any will remain in your garden to provide the desired control. As well, the ladybird beetle can only help control outbreaks of non‑mobile insects such as aphids, and is only effective if introduced before the pest population is well established.

On the other hand, there are beneficial parasitoids and predators that occur naturally in Ontario, are suited for home use, and can be bought from suppliers. Routine introductions are necessary if they are to be successful.

Related Links

• Master Gardeners
• Landscape Ontario
• Insects
• Beneficial Insects and Mites Suppliers

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