Now that Spring flowers have arrived in abundance here in the nursery, so have more (perhaps less immediately visible) garden visitors: beneficial insects. You may have used some of these good bugs, such as lady beetles, lacewings, or mantids, to control pest populations in your own garden. But did you know growers and nurseries also use a wide variety of other “beneficials” to control problem pests before plants are sold and arrive in your landscapes?
Here we’ll explain what pests are versus beneficial insects and how we use them in the nursery.
What are pests?
As warmer temperatures usher in a flush of gorgeous roses, fragrant honeysuckle and other spring bloomers here and in your landscapes, so too does it bring with it the bane of green thumbs everywhere: garden pests. But what are pests exactly?
Pests are organisms that damage or interfere with desirable plants in our gardens, fields, orchards or wildlands. In the nursery and in your garden, these pests can damage plants by feeding on foliage or burrowing into woody stems, causing visible damage and stunted growth. Some damage is just superficial and a plant can survive, but some damage can be severe enough to the point of fatality.
Many pests overwinter as eggs and hatch when the temperatures rise in the spring. That’s why you may start to see them around the same time that many of your plants leaf out and produce flowers. Some common pests we find here in the nursery and that are common in home landscapes and edible gardens include aphids, thrips and spider mites.
What are beneficial insects?
Beneficial insects, or “beneficials,” is a broad category that refers to a wide range of insects and other organisms that perform a beneficial function. Pollinator insects such as bees, butterflies and moths, for example, perform the important task of pollinating plants for fruit and vegetable production.
Beneficial insects have long been used by the nursery industry. This method of biological control is becoming visible, with increasing information available to the public in recent years. Some growers are even selling their plants with sachets of beneficials for your own home garden!
Biocontrol agents, as some beneficial insects are called, include natural enemies of insect pests such as predators, parasitoids and pathogens. Some of these insects prey on other, more troublesome insects to minimize damage to plants that those bugs can cause. Others, like some wasps, parasitize bad bugs to keep populations lower.
How do Beneficials work?
Releasing beneficial insects is a biological control method, which itself is a component of the larger integrated pest management (IPM) strategy implemented throughout the nursery, which is overseen by our IPM Manager Erica. When pests appear in the nursery, we release a variety of equivalent beneficials to establish their own populations and go after the bad bugs.
Beneficial insects that target pests fall into two categories: Predators and parasitoids.
Predators
Predators eliminate their prey by eating them. Some predators, such as lady beetles and ground beetles, chew and devour their prey. Others, like assassin bugs, predatory stink bugs, and the larvae of lacewings and flower flies, have piercing mouthparts and suck the fluids from the bodies of their prey.
Specialist predators feed on only one or a few species of prey, but most are generalists and feed on a wide variety of insect pests and even, at times, each other. They may feed on any or all life stages, including eggs, larvae (caterpillars, grubs, and maggots), nymphs, pupae, or adults. Some are predators during both their larval and adult stages (e.g., lady bird beetles), while others are predaceous only in the larval stage (e.g., lacewings) and as adults feed on nectar and pollen from flowers.
We use the following predators in the nursery:
Predatory Mite – Amblyseius fallacis
Target pests: Spider mites, russet mites, rust mites, broad mites, and other small arthropods
Amblyseius fallacis is a North American native generalist predatory mite that feeds on most mites. Unlike other predatory mites, A. fallacis can survive low temperatures and remain in areas with low levels of spider mites; able to feed on an array of pests, especially their eggs.
Predatory Mite – Galendromus occidentalis
Target pests: Two-spotted spider mites (Tetranychus urticae), McDaniel spider mites, yellow spider mites, apple and pear rust mites, Prunus rust mites, blister mites, and European red mites (Panonychus ulmi).
Galendromus occidentalis is a primary biological control agent of pest mites and is used to control mites outdoors for crops, orchards, vineyards, nurseries, and indoors for greenhouses, growing rooms, hydroponics, aquaponics, interiorscapes, and container plants. Adults are white, but once they start feeding they take on the coloration of their prey, usually red or brown.
Aphid midge – Aphidoletes aphidimyza
Target pests: Aphids, 60+ species
Aphidoletes aphidimyza larvae are voracious native predators of over 60 species of aphids. The larvae are legless maggots about 3 mm long, and orange in color which make them easy to spot in foliage. Adults are small midges resembling mosquitos that are nomadic (they will seek out heavy aphid populations to lay eggs near) and can be hard to find.
Green Lacewing – Chrysoperla rufilabris
Target pests: Chrysoperla rufilabris is a generalist predator that, in its larval form, targets aphids, thrips, spider mites, sweet potato & greenhouse whitefly, mealybugs, leafhoppers, the eggs and caterpillars of most pest moths, and more!
Green lacewing adults are green or brown, about 0.5 – 0.75 inches (1-2 cm) long. They have transparent, finely veined wings that are longer than their body. Adults are active at night and feed only on pollen and nectar, which they need in order to lay eggs. Larvae are spindle-shaped with pincher-like mouth-parts. Lacewing larvae are often referred to as alligators due to similarities in appearance.
Parasitoids
Parasitoids are small insects whose immature stages develop either within or attached to the outside of other insects, referred to as hosts. While adult parasitoids feed primarily on honeydew, pollen or nectar, immature parasitoid stages, however, are the lethal ones, feeding directly on and killing their hosts.
There are two general categories of parasitoids: endoparasitoids, which hatch within the host from eggs or larvae laid there by an adult female, and ectoparasitoids, which fasten to the outside of the host and feed through the host’s skin, sucking out body fluids.
We use the following predators in the nursery:
Small Parasitic Wasp – Aphidius colemani
Large Parasitic Wasp – Aphidius ervi
Target pests: Aphids
Aphidius species are a group of native parasitic wasps, frequently found parasitizing aphids in greenhouses and outdoor crops. Adults are tiny, dark colored, non-stinging wasps, up to 1/8 inch (2-3 mm) long. Larvae develop entirely inside host aphids, which eventually become rigid mummies when the larvae pupate. Aphidius is an outstanding searcher, and can locate new aphid colonies even when aphid populations are low.
Banker Plants
Another type of insect that is released in a nursery setting is an alternative non-pest prey. These prey are targeted by generalist predators and hosted in a special, non-crop (not-for-sale) plant called a banker plant. For example, in the nursery we raise aphids that only feed on monocots, like grasses, and place them on a host ornamental grass in our roses. These aphids don’t attack roses, but provide a food source for our beneficial predators, encouraging them to stay and feed on other, more problematic pests. These plants may look out of place, but they provide a unique system for beneficial insects to keep pests populations low.
What plants do we treat?
We release beneficial insects in many areas of the nursery. Several different plants that become hosts to pest populations; roses, spiraea and honeysuckle are common victims of aphids and thrips. Our vegetables and houseplants are kept in a covered greenhouse, and we release generalist beneficials inside to target any harmful insects there. As we expand our beneficial biocontrol program throughout the nursery, we expect to establish populations in other areas: aspens, hydrangeas and even some conifers could become hosts to beneficials. We have also noticed that when we reduce the use of insecticides, native beneficial insects arrive and feed on pest populations.
Why use beneficial insects?
The primary benefit of using beneficial insects is to reduce and eliminate pest populations. But perhaps an even bigger advantage of beneficials is the reduced use of insecticides and pesticides. While there are some pesticides that are organic and non-harmful, many synthetic pesticides are harmful to humans and animals and can cause health problems if administered incorrectly. Pesticides also contribute to decline of bee populations, and over-spraying can lead to pest-resistant populations. Beneficial insects are a chemical-free organic alternative.
Can you attract beneficial insects to your garden?
There’s an idea in gardening that having no insects in your garden is actually more harmful than having a few pests. In a healthy ecosystem, “good” bugs like pollinators and predators keep the “bad” bugs at bay. So before you reach for a pesticide and disrupt all insects in your yard, consider plantings in your garden to attract beneficials.
Some great plant options for attracting beneficial insects include carrots, celery, fennel, parsnips, legumes, broccoli and mustard greens. Also consider selections from the aster family, including goldenrod, signet marigold, sunflower, coneflower and zinnias; and selections from the verbena family, including verbena and lantana.
Dealing with problem insects may be a nuisance, most don’t cause fatal damage and can be dealt with using simple solutions, like encouraging beneficial insects in a healthy ecosystem.
