Let Beneficial Insects Work for You!

Preserving existing populations of beneficial insects can reduce the need to spray and also helps with resistance management because you will be less tempted to rely on one pesticide, which can lead to resistant pest populations.

Home to Hundreds of Species of Insects

Most landscapes and nurseries are home to hundreds of species of insects. Luckily, most are not pests in that they do not damage plants or pose a threat to human health. Many are beneficial in that they are predators or parasitoids of common insect pests. Some, such as spiders, are generalists that feed on any insect they can catch, including other predators, parasitoids or pollinators. While it is a sign of a healthy landscape to have spiders and other generalist predators present, specialist feeders such as the twice-stabbed lady beetle that feeds on scale crawlers have more impact on plant pests.

It is extremely important to learn how to correctly identify all the life stages of the most common beneficials because the larval and pupal stages look nothing like the adults. Lady beetles are a great example – we all know what an adult lady beetle looks like. Incorrectly identifying a beneficial as a plant pest can lead to unnecessary pesticide applications and eliminating those insects that help keep pest populations in check. Conservation of beneficial insects can provide long-lasting, positive results.  Scouting on a regular basis is an important component of conserving existing beneficials because you have to have a handle on pest populations as well as populations of beneficial insects.

Select the Right Pesticide

Careful selection of pesticides is critical to conserving beneficial insects. Some of the key insecticides that are compatible with beneficial insects include ultrafine (all-season) horticultural oil, insecticidal soap, spinosad, neem products and Bacillus thuringiensis (Bt).  Remember that the correct pesticide has to be selected for the corresponding pest(s) problem.  For example, a product containing Bacillus thuringiensis would work well against small caterpillars, but would have no effect on aphids. While most of these products can kill beneficial insects during the application and while sprays are wet, their short residual has less impact on beneficials coming into the area afterwards.

Landscape Design & Successful Pest Management

Landscape design can also play a major role in successful pest management with beneficial insects.  Those with a diversity of plants – trees, shrubs, herbaceous flowering plants and herbs, and even turfgrass – provide the most appropriate habitat for these useful insects. Different plant forms provide refuge for various beneficials, while those in bloom from early spring until fall provide pollen and nectar that are important food sources for certain life stages. Native plants can be especially valuable in providing food and shelter for beneficials, and should be included whenever appropriate.

Successful Biocontrol of Pests

If a decision is made to pursue biocontrol as a pest management option, whether through augmentation or conservation, a number of steps need to be followed to ensure the best chance of success. 

1. First, you have to be able to recognize the insect pests and common beneficial insects so that correct pest management decisions are made.  If naturally occurring beneficials are present are they the correct species for the pest problem? 
2. If you plan to release purchased beneficials, make sure to select the correct predator or parasitoid for the pest in question.
3. Scouting, the major cornerstone of IPM, becomes even more important if biocontrol is used.  Regular monitoring enables you to track both pest populations and the beneficial that are feeding on them.  If the beneficials are not managing the pest problem(s) at the desired level, then pesticides may be required.
4. If a first attempt is not successful, evaluate what went wrong.  Maybe the pest population was too high at the time for the beneficials to succeed as the management option, or if a release was done, it could be possible that the wrong organism and/or wrong rate was used.  Don’t give up.  Select another opportunity to try biological control again.

The beneficial insects that inhabit the landscape or nursery can play a major role in successful management of certain ornamental plant insect pests.  Think about these key advantages to biocontrol:  no toxicity concerns to the property owner and non-target organisms; no phytotoxicity damage to the treated plants; and treated pest populations will not develop resistance.

Two excellent publications that can help with identification of beneficial insects:

1. Identifying Natural Enemies (Michigan State University)
2. Gardiner, M., C. DiFonzo, M. Brewer and T. Noma. 2007. Identifying Natural Enemies in Crops and Landscapes. Michigan State University Extension, E.Lansing, MI