There are hundreds of species of beneficial insects that feed on garden pests. Meet a few of the most common ones.
• Family: Coccinellidae
Although scores of species of lady beetles (ladybugs) exist, the adults of all species are round or oval; many are brightly colored and spotted.
Females periodically lay masses of orange-yellow eggs that hatch in about five days. The larvae are elongated, usually dark in color, and flecked with orange or yellow. They can crawl rapidly over plants, searching for food. Lady beetles reproduce rapidly during the summer and can complete a generation in less than four weeks under favorable conditions. As a result, they often overtake a pest outbreak before it becomes a real problem.
The adults feed on aphids and other small, soft-bodied pests as well as insect eggs. In addition, adults feed on nectar and particularly pollen to sustain them when their prey are not available. The larvae feed on a great many insects, particularly aphids, scales, small beetle larvae, caterpillars, and insect eggs. Almost all species of lady beetles feed on insects and mites.
Unfortunately, lady beetles are slow to arrive in the spring and often leave the garden by late summer. To encourage them, try to tolerate a few pest insects, enough to provide for their increase, and plant a variety of nectar and pollen sources.
• Family: Syrphidae
With their orange- or yellow-and-black color scheme, adult syrphid flies, also known as flower or hover flies, look remarkably like bees or yellowjacket wasps. Some even buzz. However, they are harmless, visiting flowers for the nutrients that pollen and nectar provide so that they may reproduce.
The larvae of syrphid flies are tapered, legless green or gray maggots that feed on aphids; they are particularly valuable in controlling aphid infestations early in the season when it’s still too cool for lady beetles and other predators. The maggots are particularly adept at working their way into curled leaves and other protected areas that other kinds of predators are unable to penetrate. Ants, which routinely drive off other predators that threaten the aphids that they are guarding for their honeydew, apparently don’t bother syrphid fly maggots, perhaps because the maggots often cover their bodies with aphid carcasses.
Adult syrphid flies are less picky than some other beneficial insects about the types of flowers they will visit. Although preferring small, shallow flowers such as sweet alyssum, they also often visit larger flowers, such as cosmos. Be aware that syrphid flies are particularly sensitive to most commonly used persistent synthetic insecticides.
• Family: Chrysopidae
Adult green lacewings are delicate and attractive insects with large, clear, highly veined wings that are held over the body when at rest. Most feed on nectar and pollen, although some also feed on insects. The females lay small eggs on distinctive, 1/2-inch-long thin stalks either singly or in small groups on leaves.
The larvae emerge in about a week. They are similar in general shape and size to lady-beetle larvae but are usually light brown and have a large pair of viciously hooked jaws projecting from the front of the head. Often known as aphid lions, these voracious predators dine on a wide variety of insects, including—in addition to aphids—caterpillars, beetle larvae, and scales, which may be several times larger than the lacewing larvae. Several generations of lacewings are produced during the summer season, and a green-brown cold-tolerant species can be found late into the fall.
Small shallow flowers, such as those of dill, are excellent sources of food for adult green lacewings. In the absence of such natural energy sources, sprays of sugar water or sugar water and brewers’ yeast can temporarily tide them over.
• Families: Braconidae and Ichneumonidae superfamily Chalcidoidea
Thousands of species of parasitic wasps exist, each of which attacks a specific kind of host insect. Many species are very small and rarely observed. The female lays her eggs in the host, be it a caterpillar, stinkbug, wood-boring beetle, or smaller pest such as an aphid or scale. Some kinds of wasps even lay their eggs in the host’s egg.
There is usually little evidence of immature parasitic wasps in the garden because the young develop inside the host insect. However, parasitized insects may look somewhat different from normal ones. For example, aphids parasitized by wasps are typically small and discolored; they’re called aphid mummies.
When they are not looking for insects to support their young, adult parasitic wasps feed on nectar and pollen at shallow-throated flowers. An abundance of these flowers in your garden will provide them with the nutrients they need to pursue new prey insects.
Whitney Cranshaw, an entomology professor at Colorado State University, is the author of Pests of the West (1992) and Bagging Big Bugs (1995), both published by Fulcrum Publishing. He spends a lot of time in his garden, primarily because that’s where the bugs hang out.
Click here for the main article, The Most Hardworking Bugs in a Garden .