By Michael J. Holsinger, former Horticulture Agent, UF/IFAS Sarasota County Extension
Landscape insect pest problems can be among the most challenging aspects of gardening in southwest Florida.
Winter freezes help control insect pest populations in northern states but not here, where we enjoy a 12-month growing cycle.
There are millions of types of insects in our world and more than 100,000 different ones active in the United States. However, less than 1% of these actually feed on plants in a harmful way.
There are many more beneficial insect species than harmful ones. Many of these "good bugs" in fact feed on the pests, and keep them in check naturally.
In our efforts to eradicate pests in our yards we need to do more to protect these beneficials. Set schedule spraying of pesticide poisons can be wasteful and the worst thing we can do to upset the natural balance. Many pesticides do not discriminate but kill beneficials as well as pests. Pest populations can rebound faster than beneficials compounding landscape problems. Spot treatment of verified pest infestations is the preferred control method. Using least-toxic pesticides is recommended. These include insecticidal soaps, horticultural oils and formulations containing Bt, a biological control agent.
Beneficial insects fall into two categories - Predators and Parasites. Predators consume the entire host, killing it. Parasites can feed on the host, or lay eggs that produce larvae that feed on the pest.
Besides controlling pests, beneficial insects also perform other functions valuable to man. These include: pollination of crops; manufacture of medicines and pharmaceuticals, production of silk and textiles; honey and wax; and breaking down organic matter.
Here are summaries of some of the important beneficials, both in adult and larvae forms:
Assassin Bugs: Assassin bugs are generally black or brown, but many are brightly colored, and 1/2 to 1 inch in length. The head is elongate with a short, curved beak. Nymphs are just as effective in controlling pests as adults. There are more than 160 North American species. They will inflict a painful bite if handled. An example of an assassin bug is the wheel bug. It gets its name from the semicircular crest on the thorax that resembles a cog wheel.
Lacewings: Lacewings are common insects, found on weeds, cultivated row crops and shrubs. They are greenish or brownish, about 3/4 inch in length. The wings are transparent with many veins. About 87 species occur in North America. The adults may be predaceous or feed on pollen. Lacewing larvae are elongate and have large sickle-shaped mandibles. They are commonly called aphid lions and feed on aphids, other small insects and eggs.
Lady Beetles: Lady beetles are among the best known and most beneficial insects. There are about 475 species occurring in North America. Both the adults and larvae of lady beetles consume aphids, immature scale insects, mealybugs, mites and other soft-bodied insect pests as well as insect eggs. Adult lady beetles are oval shaped and most are orange or reddish with black markings. Most lady beetles are about 1/4 inch long.
Many lady beetle larvae are elongate, somewhat flattened and covered with small spines. They are usually dark or black with bright colored spots or bands. The legs are long and slender. Some lady beetle larvae are covered with a white flocculent secretion and resemble pest mealy bugs. Studies have found that 200-500 aphids are consumed during the larval stage. The adults are usually even more voracious.
Syrphid Flies: Syrphid flies are commonly found on flowers and are also known as flower flies or hover flies. This is a large group consisting of about 900 North American species. The flies vary greatly in color and size, but most are yellow with brown or black bands on the abdomen. Many resemble wasps, others closely resemble bees, but none sting. The flies have the ability to hover in flight for long periods. Many syrphid fly larvae are predaceous especially on aphids
Parasitic Wasps: Parasitic wasps are an extremely important and large group of beneficial insects with about 16,000 species occurring in North America. These wasps are very small, most less than 1/8 inch long and usually not noticed. Some wasp larvae feed and pupate inside the host and the emerging wasp leaves a small circular hole in the body of the host as evidence of parasitism. Many harmful insects such as aphids, whiteflies, scales, leafminers and caterpillars are parasitized. Other parasite larvae live on the outside of its host where they construct numerous small, white cocoons attaching to the body of the host.
Tachinid Flies: Tachinid flies are parasitic in the larval stage and are a valuable asset in keeping many of our serious pests in check. There are about 1,300 North American species. Many tachinids resemble the common housefly, but are a little larger. Others are bee- or wasp-like in appearance. One tachinid fly, the red-eyed fly, was brought in from South America as a biological control for the mole cricket.
Earwigs: Many earwigs are predaceous upon lawn insect pests such as chinch bugs, small mole crickets and sod webworms. This is a large species up to 1 inch long with mandible-like pincers in the abdomen. In laboratory observations they consume up to 50 chinch bugs a day.
Big-Eyed Bug: This insect resembles a chinch bug except for its enlarged eyes. They love to eat chinch bugs, small caterpillars and soft-bodied insects on the soil surface. They are up to 1/8 inch long.
Spiders: Spiders are not true insects, but arachnids. They feed on a wide variety of insects. The majority captures their prey in webs, but some such as the jumping spider, pounce on victims. The latter are especially effective in capturing insects that inhabit the soil surface or plant foliage. Only a few spiders such as the black and brown widow, tarantula, and brown recluse are poisonous to man.
Bees: Bees are among the most important pollinators. With decimation of native honeybee colonies from disease and mites, ground-dwelling bumble bees, have become more important.
Butterflies: These beautiful creatures are valuable pollinators and contribute esthetically to our gardens. However, caterpillars of some butterflies can damage plants by defoliating them. More than 100 species of butterflies occur in Florida.
Dragonflies: Dragonflies, also nicknamed "mosquito hawks" consume significant numbers of mosquitoes and other flying insects. They are sensitive to pesticides and their presence indicates an environmentally friendly garden. Dragonfly nymphs are aquatic and can help to control mosquito larvae before they become biting adults.
Golden Silk Spider: This spider is found throughout Florida. The female is distinctively colored and among the largest orb-weaving spiders in the country. Males are small, dark brown in color and often found in the webs of females. These spiders feed primarily on flying insects, which they catch in webs that may be more than a meter in diameter. They are most commonly found in forests, along trails and at clearing edges.
Giant Swallowtail: The adult butterfly has a wingspan of 3 to 6 inches. The upper surface of the wings is brown with a row of large yellow spots along the margins and a prominent diagonal yellow band. It is often seen taking moisture at mud puddles and at damp sand. The giant swallowtail larva is a caterpillar 1-2 inches long with a blotchy brown and white pattern. It can look like bird droppings. These caterpillars feed primarily on citrus in Florida and are called 'orange dogs' because they are often found in orange groves.
Jumping Spider: All species are small, usually less than 15 mm long. They are identified by their eye arrangement, which is in three rows. Jumping spiders do not construct webs, but actively hunt prey during the day, pouncing on victims. Many are brightly colored, sometimes with iridescent mouthparts.
Ladybug: About 475 species occur in North America. Both adults and larvae are predaceous on aphids, mealy bugs, mites, scale and other pest insects, eating scores in a given day. Adults are oval-shaped with orange, or reddish with black markings or black with yellow or red markings. Most are about 1/4 inch long. The larvae are elongate, flattened with small spines, usually dark or black with brightly colored spots or bands.
Monarch: The monarch may be the most familiar U. S. butterfly. It has gotten lots of publicity because of its migratory flights to Mexico, although it can maintain residence year-round in South Florida. It is bright orange, with a white-spotted black border with black-outlined veins. The male has a black patch in the middle of each hindwing. The larval caterpillars are dramatically ringed with yellow, black and white on each segment. Adults feed on and pollinate many perennial flowers, especially the milkweeds.
Praying Mantids: These are large scary-looking insects usually over 2 inches in length and may be green or brown. There are only 20 species in the U. S. and Canada but more than 1500 worldwide. The front legs are modified for grasping and holding prey. They wait patiently among the foliage, legs in an upraised position, for unsuspecting insects. Mantids have a triangular head and are the only insects able to look over their shoulder. The egg capsules of mantids contain 200 or more eggs arranged in a pattern deposited on twigs or stems.
Predatory Stink Bugs: The most familiar stinkbugs to gardeners are those that are crop destroying. However some stinkbugs are beneficial. These can be identified by spines projecting from their thoraxes, whereas plant feeders have round shoulders. The predaceous forms also have short, stout beaks while plant-feeding forms have long, thin mouthparts. The predators feed on many insects, especially caterpillars.
Cloudless Sulphur: This large yellow butterfly has a wingspan of 2 inches. It migrates through Florida annually and shows a preference for red blossoms such as those of the shrimp plant, railroad vine, turk's cap and hibiscus. The caterpillar has a pebbly surface and bears a distinct lateral yellow stripe running the length of the body. The larvae feed on Cassia.
Green lynx spider: This spider is commonly encountered on shrubs, weeds, and foliage. The body is a vivid, almost transparent green, with red spots and some white markings. The legs are long, slender and covered at intervals with long black spines. These spiders have good eyesight and stalk their prey during daylight. They spin no webs but sometimes anchor themselves with silk. They are important predators of caterpillars.
Polistes Wasps: Also called paper wasps, they are primarily predators of caterpillars. The caterpillars are stung and paralyzed then placed in the individual cells or chambers of the nest as food for developing wasp larvae.
Cicada Killer Wasp: This wasp is 16mm long and back in color with pale yellow markings on the last three abdominal segments. It is a solitary wasp but colonies nest in the same location, each female digging a hole up to 10 inches deep. It stings and paralyzes cicadas and a closely related species attacks and kills flies.
Yellowjacket: It is about 12 mm long and has alternating yellow and black markings on the abdomen. The wasp is very aggressive in defending itself or its nest. The stinger is not barbed so the wasp can sting repeatedly.
Pest Management Practices to Protect Beneficials
1. Monitor the landscape for pest problems. This does not mean checking every plant or examining every blade of grass. Concentrate on plantings that have had pest problems in the past. Look at the undersides of leaves.
2. Do not spray preventatively. Apply pesticides only when pest insects are present and causing unacceptable damage. Spraying on a set schedule can be wasteful. There may not be many pests to kill. It can also kill beneficials that are keeping pests in check causing a pest explosion. A few pests around are okay and provide necessary food for beneficials.
3. Spot treat only the problem areas. If insect pests are concentrated on only one or two plants, you do not need to spray every plant of that type in the yard. In fact pruning a concentrated infestation into a garbage bag could solve the problem. If an area of the lawn is infested with chinch bugs or mole crickets, treating it and a buffer of a few feet is probably sufficient.
4. Use least toxic materials for control of most insect pests. Insecticidal soaps and horticultural oils can control insect pests such as aphids, thrips, whiteflies, mealy bugs, and scale. Formulations of Bt (Bacillus thuringiensis) are biological controls for caterpillars especially when small. A homemade solution of one teaspoon of mild dish detergent (not with a degreaser) and one tablespoon of vegetable oil added to a gallon of water is an effective insecticide. It's a good idea to test materials on a section of foliage to check for phytotoxicity and do not spray in windy weather or the heat of the day.