Fort Bend County Master Gardeners Beneficial Insects We know very little about specific conditions necessary for attracting specific beneficials in Houston. There are likely to be many specific plants and conditions which will take years to straighten out. There are many biology papers to be written in the local universities or by amateur naturalists! For example, it has been found that in some places pine trees discourage plum Curculio on peaches; that mustard flowers encourage a predator of cabbage loopers, that a parasite of the grape leaf hopper needs wild blackberries. But are these findings true in Houston, and what do you have to do to apply them? Nevertheless, below I give what I have found out about attracting specific beneficial insects. Attracting Spiders Spiders eat all sorts of insects. Wolf, jumping, and lynx spiders prefer a close, shadowed retreat near the ground They are reported to like ageratum, asters, petunias, polygonium, sweet allysium, and hypercium. The black and yellow argiope orb spider, by contrast, prefers nearly any branching bush waist to eye high in sun. I have seen them spin their webs and egg cases on tall iris, low shrubs, blackberries, and bell peppers. They attach their egg cases to these, so short lived annuals like peppers are a bad plant for them to breed in. Attracting Beneficial Beetles Dark, shiny, ground beetles eat slugs, snails, and soft bodied larvae such as caterillars. They live just below the ground and hunt by night, preferring a cover such as mulch, rocks, or boards. They are common under concrete shim blocks around raised beds. Ladybugs eat small soft insects such as mites, aphids, scale, whiteflies and their relatives. Their larvae eat more than the adults. Butterfly weed, angelica, marigold and yarrow attract them to the garden. Soldier beetles feed on aphids, cucumber beetles, spider mites, caterpillars, eggs, so any plants that have these pests (such as wild goldenrod) will attract them. They also eat ladybugs. Adults are common on grasses, goldenrod, milkweed, hydrangea and other plants. As larvae, net-winged Beetles eat insects, but as adult are attracted to nectar and plant matter. The Adult Checkered Beetles have different diets depending on species. Most adults eat nectar, but one species eats thrips. Larvae of different species prey on the larvae of woodboring insects and on various wasps and bees. Attracting Beneficial Bugs Assassin bugs eat a wide variety of pests including caterpillars, aphids, bean beetles, leafhoppers and hornworms, and beneficials such as honey bees. Sunflowers especially attract them. 1
Damsel bugs eat most small pests, and need low plants and ground covers to succeed. Toad bugs breed near water and inhabit wet areas eating small insects. Attracting Beneficial Flies Hover flies and hover fly larvae eat aphids, mealybugs, thrips, and leaf hoppers. They like cosmos, dwarf morning-glories, marigolds, spearmint, baby blue-eyes, and the herb meadowfoam. Robber flies eat all sorts of flying insects, and their larvae live in mulch and loose soil, and eat eggs and grubs below the soil. The adults need a constant supply of flowering plants. Adult tachinid flies feed on nectar and to some extent on honeydew secreted by whiteflies and their relatives. Hart believes they are the most important garden predator of all. Depending on the species of tachinid, their larvae feed on certain borers, beetles, bugs, especially caterpillars, armyworms, etc. The tachinid fly particularly eats squash bugs, stink bugs, leaf-footed bugs, cotton stainers and other true bugs that bother tomatoes and other fruits. Tachinid adults are drawn especially to buckwheat. Dance flies eat small insects, and the larvae are predacious. They need standing water to breed. Long-legged flies prefer damp wood-like places, fields, and water places where they attack insects visiting flowers. Adults of the Texas long-legged fly eat spider mites. Attracting Beneficial Net-Veined Insects The net-veined insect order Neuroptera contains several families of insects whose larvae eat insects or parasitize them. Ant lions, owl flies, mantidflies and green lacewings all consume huge numbers of insects. Juvenile lacewings eat corn earworms, aphids, spider mites, leaf hoppers, thrips, mealy bugs, etc. Angelica, red cosmos, coreopsis, tansy, goldenrod, and Queen Anne's lace all attract them, as does citrus and other plants which attract whitefly and its honeydew. Attracting Beneficial Parasitic Wasps The braconid wasp drinks nectar as an adult, but its larvae eats caterpillars of the hornworm moth, gypsy moth, and other moths. They prefer single blossomed wild flowers and flowering herbs. The ichneumon, chalcid, tiphiid, and pelecinid wasp adults drink nectar and water. The ichneumon larvae are a major control of insect populations through parasitizing them. The chalcid larvae parasitizes aphids, scale, mealybugs, and large flying insects. The pelecinid and tiphiid wasp larvae parasitize May beetle larvae and other soil beetles. Southern peas, fava beans, and buckwheat all attract parasitic and predatory wasps. 2
Attracting Beneficial Predatory Wasps There are several vespid wasps: the paper wasps, the hornets, and the yellow jackets. They are attracted to the pollen from the daisy family such as oxeye, strawflowers, blackeyed Susan, goldenrod, and yarrow. The paper wasp adults drink nectar and the juices of rotting fruits and pre-chews insects for larvae. They make nests in spring of wood pulp and saliva and are very tolerant of humans. Paper wasps have reddish brown coloring (especially on abdomen) with yellow rings, while the much more aggressive yellow jackets and hornets are black with yellow or white markings, or yellow abdomens. The hornets and yellow jackets nevertheless eat many insects and pre-chew insects for larvae. The hornets are dangerous only around their nests in a tree or outbuilding or low cover depending on species. Yellow jackets will sting with much less provocation, so don't move hand or foot into unfamiliar plants without looking first. As well, there are sphecid solitary hunting wasps such as mud daubers. Both adults and larvae of these eat a lot of insects and spiders. Some species adults just eat nectar. Encarsia formosa is a 1/40 inch native predatory wasp which eats huge numbers of whitefly. Both Encarsia and whitefly have slower metabolism around rose geraniums. These are for sale and can be established in gardens. Attracting Beneficial Dragonflies and Damselflies All of the order Odonata require water for breeding, so a pond and aquatic plants is the key to attracting them. The Odonata include damers, gomphids, adders, skimmers, and a variety of other dragonflies and damselflies. All adults feed on flying insects including mosquitoes, and some such as the damselflies eat aphids and other soft-bodied insects. Beneficial and Pest Insects Most pests and beneficials are of course insects. To make insects work for you, you need to understand them. Insects have six jointed legs, and generally are found either in their early larva stage when they are wormlike, or later during their usually winged adult stage. There are 26 different biological orders of insects, and about 100,000 species in North America. Even with a magnifying glass and very good identification materials, it is difficult to distinguish beneficial insects from harmful ones. In Houston, there are biological orders of insects which neither bother plants nor eat pests, and there are orders such as those of fleas, lice, flies, mosquitoes, and termites whose significance is not mainly horticultural. The remainder are divided as follows: Significant Beneficial Insect Orders. The insect eating dragonfly & damsel fly order Odonata. These beneficials eat huge numbers of mosquitoes, but must have water to breed. The insect eating Lacewing and Ant lion order Neuroptera These eat a large number of aphids, and lacewings eat cabbage loopers, corn earworm, squash vine borer, tomato hornworm eggs, leafhoppers, mealy bugs, spider mites, white fly and mealy bugs. 3
The insect parasite order Strepsiptera These eat leaf hoppers, mealy bugs, phylloxera, scales, whiteflies, and aphids in the pest order Homoptera. Insect Orders Containing Beneficial And Pest Species The Grasshopper, Locust and Mantis Order Orthoptera This order contains the grasshopper, katydid, cricket, locust, walking stick and mantis. The last two are sometimes put in separate biological categories. All of these except the mantis eat leaves. None are much of a problem except for grasshoppers on hibiscus. The mantis eats a few insects such as aphids, bean beetles, and tomato hornworms. The Carolina mantis is a native that eats all sorts of insects, it particularly likes goldenrod flowers. The Praying Mantis is a European import now naturalized in the East and often sold in Houston. It got its reputation as a beneficial because it eats Gypsy Moth caterpillars, but it is ineffective as a control. The True Bugs Order Hemiptera This order contains harmful insects such as the brown, green, and leaf footed stink bugs, the occasionally bothersome chinch bug; the squash bug; the tarnished plant bug; and the lace bugs. This order also includes the very beneficial insect eating assassin bugs, ambush bugs, and spined soldier bugs. The assassin bug just about covers unsprayed pest infected plants in the Houston summer! Assassin bugs eat aphids, cabbage loopers, corn earworms, tomato hornworms, some leafhoppers, bean beetles, squash vine borers. Ambush bugs eat spider mites, as well as honey bees. Soldier bugs eat caterpillars and grubs, corn earworms, cucumber beetles, and bean beetles. The beetle and weevil order Coleoptera This includes the bean beetles, cucumber beetles, asparagus beetles, blister beetles, the flea beetles which destroy many spring greens, the root eating white grubs of June beetles, as well as the insect eating ground beetles, and lady beetles (ladybugs). Firefly beetle Larvae eat slugs and snails and spider mites. Of the weevils, the plum curculio and the pecan weevil do by far the most damage. Beetles go through a development cycle from egg to larval grubs and borers, to pupa to adult. Beetles that are large or have long, scissor like snouts or hairy jaws are generally beneficial, while shorter jawed ones are plant eaters. Ladybug beetles eat aphids, citrus mealy bugs, spider mites, bean and cabbage weevils and whitefly. Ground beetles eat slugs and some snails. Rove beetles eat mites, small insects, and small worms and slugs and snails. Beetle larvae eat corn earworms. The Lepidoptera order of butterflies and moths. This order contains many leaf eating and boring larvae, as well as beneficial flower pollinators of the pawpaw and all the beautiful butterflies (see ornamental chapter). It 4
includes the squash vine borer, the various peach tree borers, cutworms, armyworms, cabbage loopers, corn earworms, tent caterpillars, leaf rollers, berry moths, fruit worms, and hornworms. The fly order Diptera This includes harmful vegetable maggots, fruit flies, leaf miners, and the beneficial insect eating hover flies, robber flies, syrphid and tachinid flies. Syrphids eat aphids. Tachinids eat cucumber beetles. The thrips order Thysanoptera This consists of two families: the tiny, plant-sucking insects-the common thrips family-that deform and brown flower leaves and fruit, and spread tomato spotted wilt. They are easily seen in a white rose by spreading a partially opened bud. The order also includes the beneficial banded thrips family which eat thrips, moth eggs, mites, and small insects. The Ant, Bee, and Wasp Insect Order Hymenoptera This includes the mainly troublesome waste-recycling ants, the beneficial pollinating honey bees, carpenter bees, and bumblebees, and the highly beneficial, insect-eating, pollinating wasps: the predatory yellow jackets, hornets, mud daubers, and the tiny parasitic chalcids, tricogrammas, and braconids. Many of the Hymenoptera bite or sting, but only if their nests are threatened. They are very valuable, so the wise gardener leaves them alone, and looks carefully before thrusting an arm, leg, or tool into a thicket of asparagus, salvia, or tall weeds. Wasps eat cabbage loopers, corn earworms, cutworms, flea beetles, tomato hornworms, bean beetles, and most caterpillars. Parasitic wasps lay eggs in pests and their larvae eat their way out of cucumber beetles, some leafhoppers, and (sometimes) squash vine borer. Trichogramma wasps eat aphids. Chalcid wasps eat citrus mealy bugs. Killing a Bad One Kills a Good One From the above, it should be obvious that the would-be gardener has a lot of biological homework to do if pest control based on poison is to work. Any attempt to kill a pest runs the danger of killing a beneficial insect that is either biologically related, or that eats the pest for dinner! Go organic! Randall, Robert, Year Round Vegetables, Fruits and Flowers for Metro Houston, Tenth ed. 1987-1997, 1999-2001, Twelfth ed. 1999, 2000-2006 5