Laidback Gardening with Robert Kourik
The Good Insects
Flower diversity equals insect diversity. This is important for attracting beneficial insects. But, like a two-sided coin, flower diversity attracts what we call pests. For example, in early spring aphids colonize my blooming fava beans. The predators, ladybugs, syrphid flies, and parasitic wasps do follow shortly. As spring progresses the aphids move on to other plants, as do the good guys.
Of all the bugs in the world, the lady beetle is practically the symbol of organic garden insects. It’s become well known for its aphid-eating proclivity — both the adult beetle and the larvae eat only aphids. Unfortunately, to purchase lady beetles for aphid control means, according to Dr. Ken Hagen of UC Berkeley, you are “simply throwing [your] money away.” The lady beetles sold by mail order and through nurseries are captured from large winter congregations in the Sierra Nevada. Entomologists have discovered that these insects gather each fall with plenty of stored fat for both the winter and part of the spring. Unless the lady beetles are defatted before sale, the awakening lady beetle isn’t even hungry. Hagen says, “ Hippodamia convergens gathered from aggregations in the Sierras [are] ineffectual predators; green lacewings are better.” The ladybug is more inclined to leave your yard. (Those that do hang around eat up to 5,000 aphids in their lives. The young larvae eat up to 400 aphids before they form a pupa.) Also, up to 10 percent of the overwintering lady beetles have parasites; selling the beetles only speeds up the spread of these parasites. While parasitized beetles do eat, they can’t reproduce.
You can lure ladybugs to your garden with the same beneficial plants that attract most good bugs — members of the sunflower and parsley families. Also, you must stop spraying with anything; yes, skip even the “organic” sprays as they are often too broad-based to protect the ladybugs and their larvae.
The larvae look like small, creepy bugs and are often mistaken for a pest. The soft-bodied larvae are very susceptible to all manner of pesticide sprays, chemical and organic. Treasure the ones that are black with one orange spot on each wing; they don’t fly away to congregate in the mountains each winter. They stay in your garden in ground litter to revive in the spring. They are called the twice-stabbed ladybug. They are mainly predators on scale and prefer arboreal habitats.
Plantsthatattractladybugsincludefern-leaf yarrow, common yarrow, carpet bugle weed, basket of gold, dill, Queen Ann’s lace, and more.
Syrphid fly larvae are some of the most voracious predators of aphids. They are little known, and the larvae are easily mistaken for slugs, so they are often killed. And there are plenty of syrphid flies (also called a hover fly). One common genus of hoverfly has over 300 species of hoverflies, just on the American West Coast.
The syrphid fly (of the family Syrphidae) is often mistaken for a bee or wasp. With their various horizontal yellow and black striping, they look like a honeybee. The difference is the syrphid fly lives up to its other name — it hovers in the air like a helicopter in front of flowers. Bees can’t do this. The subsequent larvae eat lots of aphids. Often a single larva can eat many times its body weight in aphids in its life. The hoverfly larvae are much better predators of aphids than ladybugs. The adults should be treasured as they fly from flower to flower to gather the nectar and pollen they need to survive. Because the larvae look like tiny slugs, they are also mistaken for a pest and squished or sprayed. Poor little guys get it on all fronts. And don’t forget that all sprays, organic or chemical, will kill its favorite food — aphids — as well as all other insects, whether they are beneficial or not. Watch to see if the plant has such a low level of aphids that it is not a problem and leave the plant alone as nature maintains its natural balance. The good guys can’t survive without some of the bad guys.
If you have ever paused near a patch of cosmos on a sunny summer afternoon, you are certainly familiar with the unique flight of the hoverfly, as it zigzags about the blossoms, occasionally stopping in midair, its shimmering wings barely visible. There is no mistaking it. Unlike other winged insects, flies in the order Diptera (meaning two-winged) have only one pair of flying wings. The second pair of wings is reduced to two little knobs, the halters; these function like miniscule gyroscopes, allowing the flies to quickly change direction — a useful ability when being chased by predators or a biped armed with a swatter. Not that the conscientious gardener would want to swat most syrphids! With few exceptions, hoverflies are among our most abundant and helpful garden allies.
In one study, phacelia attracted both bees and hoverflies. The favorite flowers of syrphid flies are the daisy ( Asteraceae) and umbel ( Apiaceae) families. They also feed on nectar and pollen in a wide range of other plant families, including rose ( Rosaceae), buckthorn (Rhamnaceae), borage ( Boraginaceae), and willow ( Salicaceae).
In a thesis by Elsa Laubertie, it was found that, in order of attractiveness, Phacelia (Phacelia tanacetifolia), followed by buckwheat ( Fagopyrum esculentum), and then coriander ( Coriandrum sativum) had the best reproductive potential for feeding female syrphids. And the hoverflies that had fed on phacelia and buckwheat pollen were found up to 17.5 meters (57 feet) from the floral areas. This means the beneficial flowers can be planted just about anywhere in the average yard and attract plenty of syrphid flies.
Robert Kourik is the author of “Lazy-Ass Gardening,” “Understanding Roots,” “The Insectary Calendar,” “Drip Irrigation for Every Landscape,” and All “Climates,” and his new book, “Sustainable Food Gardens.”