Beneficial Insects and Mites
Insects or mites that eat or parasitize pests are often called beneficials, natural enemies, or biological control agents.
The majority of insects and mites are not pests. Most crop pests are attacked by beneficial insects that help to control or suppress the pest. Therefore, it is important to recognize beneficial species and to conserve their populations. They can occur abundantly in crops where the pesticides are used carefully, which can include reducing the number of applications if possible, choosing pesticides that have lower/no impact on beneficials, and timing applications for when beneficials are not active in the field.
Beneficial insects and mites belong to three categories: predators, parasitoids, and pollinators.
Predators capture and eat other organisms such as insects or weeds. Examples are larvae and adults of ladybird beetles, ground beetles and brown lacewings, larvae of syrphid (hover) flies, green lacewings, aphid midges (Aphidoletes) and yellowjacket wasps.
Ladybird adults and larvae and lacewing larvae feed on aphids and other soft-bodied insects. Adult syrphid flies resemble yellowjacket wasps in colour; they can often be seen hovering around flowers. Ground beetle larvae live in the soil and feed on soil dwelling pests such as caterpillars, cutworms and slugs. Spiders and predatory mites are also highly beneficial. Spiders feed almost entirely on insects, and predatory mites feed on plant-feeding pest mites. Ants are predators of many insects, but some protect aphids to feed on their honeydew.
Predators that may be available for direct purchase include predatory nematodes, ladybugs, preying mantids, mealybug predators, and predatory mites for control of spider mites, thrips and fungus gnats. Purchasing ladybird beetles for release outdoors is not recommended as they usually just fly away. However, they can be very helpful in managing pests in greenhouses and solariums.
Insects that parasitize other insects and arthropods are referred to as parasitoids. The immature stages of parasitoids develop on or within its host, eventually killing it, before emerging as adult parasitoids. Parasitoids may attack all stages of their host – eggs, larvae, nymphs, pupae, and adults. Examples of parasitoids are aphid and whitefly parasitoids, which lay their eggs inside aphids and whiteflies. Tachinid flies lay their oblong white egg(s) on the outside of their host (usually caterpillars). When the eggs hatch, the maggots bore into the caterpillar. The caterpillar may die or develop into a pupa. In either case, a tachinid fly, not a moth or butterfly, will emerge from the caterpillar or from the pupa.
Pollinators include honeybees, leafcutter bees, other wild bees, some flies, butterflies, moths and other insects that visit flowers to feed on nectar and pollen. Pollinators are critical to crop production. Most commercial fruit growers rent honeybee hives to place in their orchards during the blossom period. Greenhouse vegetable growers use bumble bee hives to pollinate some crops.
Protecting and Promoting Beneficials
In Commercial Crops:
- Practice Integrated Pest Management by including cultural practices in your pest management program and using pesticides only if necessary. Treat when the pest population reaches a damage threshold. The threshold and guidelines will vary depending on the pest and the situation
- Some pesticides are more harmful to beneficial insects than others. Use the least harmful (‘soft’) products such as horticultural oils or biopesticides whenever possible. Consult your Crop Production Guide for recommendations and warnings. Some fungicides and herbicides can also be harmful to beneficials
- Do not apply any pesticides that are toxic to bees or pollinators during the blossom period or while hives are located in the crop
In the Home Garden:
It is not necessary (or possible) to eliminate all insect and mite pests. Remember that a few insects will not cause noticeable harm, and they will provide a food source for maintaining beneficial organisms.
The following practices will help conserve beneficial insects:
- Be able to distinguish beneficials from pests
- Practice Integrated Pest Management and rely primarily on cultural practices in your pest management program
- If pesticide application is needed, use the least harmful (‘soft’) products such as horticultural oils or biological controls whenever possible
- Apply pesticides only where pests are causing injury (spot treat)
- Leave refugia for beneficials. Unsprayed infested plants provide food and freedom from spray residues
- Cover refugia plants to protect beneficials when spraying pesticides that could impact beneficials
- Provide flowering plants which serve as nectar and pollen sources for beneficial flies and wasps. Examples include mustard, daisies, wild carrot, yarrow, buckwheat, goldenrod, anise, clover, milkweed, and black-eyed Susan. However, be careful not to introduce weedy or invasive species
If you are releasing beneficial insects into your garden, you may need to release the beneficials more than once at regular intervals, starting early in the growing season