Hardworking Bugs

Image Gallery Syrphid fly Photography by Whitney Cranshaw

ON A SUNNY AFTERNOON in the herb garden, you pause and lean closer to smell a flower, check on a new transplant, and pull a weed. Suddenly you notice dozens of aphids working on the new leaves of your oregano, but before you have time to worry, you see that help is on the way. Other bugs are also roaming the plants, apparently feeding on the pests.

Most gardeners realize that many kinds of insects in a garden can be beneficial in managing the damaging kinds that also occur there. Many can recognize the more familiar ones—lady beetles, green lacewings, even some of the parasitic wasps that dine on garden pests. Not often, however, do gardeners give much thought to the needs or cultivation of these naturally occurring biological controls.

Beneficial insects have environmental needs that parallel our own: a good place to raise their young, food to sustain the young and the adults, a bit of shelter, and freedom from harmful gardening practices. Fulfilling these needs for them can improve the efficacy of biological controls.

The immature stages of many kinds of beneficial insects look quite different from the adults and have different food requirements. A few bugs to munch on is their primary need. Some protection from winds, a bit of mulch, or a place to nest are usually all that they need in the way of shelter. Limiting ­pesticide applications or selecting products such as soaps, Bacillus thurin­giensis, and neem, which have little ­­­ef­fect­­ on beneficial ­insects, can help control pests ­without wiping out the complementary efforts of natural controls.

Although nearly every garden provides food for the young of beneficial insects, not all of them meet the food needs of the adults. Many adult beneficials sustain themselves on nectar for energy, and some need pollen as a source of protein and vitamins. For example, syrphid flies, whose maggotlike young are among the most effective controls of aphids in a garden, must feed on nectar and pollen before they can produce eggs. The adult stages of many lady beetles, parasitic wasps, and green lacewings similarly depend on flowering plants for sustenance, and the absence of these plants can greatly ­reduce their effectiveness as biological pest controls.

Not all flowering plants produce sufficient nectar or pollen for beneficial insects. Others are the wrong shape: the deep-throated flowers that attract butterflies, bees, and hummingbirds are quite inaccessible to insects with short mouthparts.