Week 9 - Beneficial Insects
For episode/article 9 for This Week in the Garden, we’ll cover beneficial insects in the garden. Like last week’s article/vlog, this topic is a difficult one to cover in a short amount of time and is something I could and have spent a full 2 hours teaching. With that being said, I won’t subject you to that and I’ll do my best to show you some generic groups of beneficial insects and how to promote them in your garden.
Part of the reason this topic is so difficult to simplify is that beneficial or “good” insects are subjective. My favorite example of that is paper wasps. Most people think of wasps as pests; they build nests under eaves and can sting if threatened. Yet, in the garden, wasps can be beneficial. They are avid predators of caterpillars and can greatly reduce their populations. This example helps show that insects can be both “good” and “bad” depending on the environment they are in.
But what about a garden “environment”? In a typical vegetable garden, beneficial insects can be simplified to those that help produce fruit and those that protect the plants. Insects help produce fruit by pollinating flowers - carrying pollen from one plant to another. Additionally, insects can benefit a garden by protecting the plants from other insects. This is most commonly done through predation and parasitism.
Pollinators
When we think of pollinators, we mostly think of bees and butterflies; however, moths, flys, and ants are all exceptional pollinators in various plant systems. In the garden, the overwhelming majority of pollination occurs by bees. In fact, most of the butterflies and moths that interact with vegetable gardens are pests in the caterpillar stage. The two bees of note are the honey bee and squash bee. Honey bees are more of a generalist and will pollinate a number of vegetables. Squash bees on the other hand are specific to cucurbits which include squashes, watermelon, pumpkins, and cucumbers. There are dozens of other bees that pollinate gardens and if you’re interested in learning more about them, here is a great guide from N.C. State University.
There are a number of ways to promote bee habitat. The first and probably most obvious is to provide them more food, “if you feed them, they will come”. This can be as simple as planting native flowering plants along your garden or around your house. Planting a larger garden will also help draw in pollinators. Aside from food, shelter is the next most important factor to benefiting or pollinators. Most of our native bees nest either in the ground or in stems. To help, watch out for ground nests in your garden and build a bee hotel. Bee hotels are a fun project for the family and require little upkeep. For more information on bee habitat and native flowers, check out the nonprofit Xerces Society.
Predators
There are a large number of predatory insects from a wide range of insect families. In general, you won’t see predatory insects in your garden until you have an insect pest population. For that reason, a lack of predators isn’t a sign of an unhealthy garden. I’ll include a slideshow of common predators to vegetable gardens, but the most common include: predatory bugs (assassin, ambush, stink bugs), lady beetles, lacewings, syrphid flies, ground beetles, and paper wasps.
Promoting predators is similar to promoting bee habitat. Native plants promote insect life and will draw in predators. Leaving weeds and other plant material outside of the garden will also promote insect life, but can increase your pest problems as well. Similarly, straw or hay mulch in the garden will increase ground predators but can increase pests like slugs and snails.
Parasitoids
Parasitoids are arguably the most important and most forgotten beneficial insects in our gardens. They reduce pest populations by laying their eggs in host pests, either in their eggs or in the larvae/adults. Parasitoids are most commonly seen on caterpillars, but there are a few that parasitize bugs as well. In general, these insects are tiny wasps that most people would assume are gnats.
The best way to promote parasitoids is by planting native flowers. A number of these insects feed on nectar and pollen and are drawn to flowers. If you notice insect pests that have been parasitized, usually a dark color or with visible eggs/cocoons, leave them in the garden. This will allow the parasitoids to complete development and further protect your gardens.