| It seems like caterpillars can move in overnight, making fast work of plant material. These little machines with their strong mandibles are designed to do one thing—eat, and eat a lot. But it’s funny to think as adults we often want them around for their beauty and pollination abilities.
Identification
Most of us know from elementary school what a caterpillar looks like, but what you may not realize is that some of them have excellent ways of disguising themselves. Caterpillars can be smooth-skinned like armyworms or sometimes “hairy” or barbed like saddleback caterpillars. These hairs can be modified to sting, so unless you know what you are dealing with, it’s best not to handle them bare-handed.
 Tent caterpillars protect themselves by spinning tents of silk, making it hard to penetrate them with insecticides.
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Another way to identify caterpillars is by the number of legs. Most caterpillars typically have three pairs of legs on the thorax (the front part of the caterpillar) and two to five pairs of fleshy prologs on their abdomen. This is important because there are some wasp species (such as sawflies) that, from a distance, may look like caterpillars but are not. Sawflies have six or more fleshy prologs.
Positive identification is critical because management approaches may be different, as well as pesticide selection.
Caterpillar feeding
Depending on the species of caterpillar, the damage can take different forms. Some caterpillars will consume entire leaves, whereas others may just eat holes in the plants.
Skeletonizers will feed on leaf surfaces, scraping away only the top layer of the leaf and causing significant damage. Leaf-roller caterpillars will attach leaves together with silk and hide within the leaves. Tent caterpillars protect themselves by spinning tents of silk, making it hard to penetrate them with insecticides. Early application when caterpillars are small is key to controlling this pest.
The life cycle of caterpillars is similar to many other insects that have complete metamorphosis. They start out as an egg, laid individually or in a group. Once the egg hatches, the larvae emerge and begin to feed on the host plant. Most caterpillars are host-specific. This often works to a grower’s advantage because you can frequently identify pest caterpillars by the plant it is feeding on. The larvae go though a series of molts until they reach a certain size. They stop feeding and search for a place to pupate, emerging later from their pupal cases as winged adults.
Other caterpillar species
There are some pests that you may not realize are caterpillars.
Bagworms. To protect themselves, these caterpillars build structures around their bodies. They use silk to stick debris around their body, making a camouflaged mobile home. They can still move around and feed on plants, but most of the females will never leave because they lack wings.
Leafminers. Positive identification can be tricky sometimes because leafminers can be either flies or caterpillars. Some examples of a caterpillar miner are the azalea leafminer (Caloptilia azaleella Brants), arborvitae leafminer (Argyresthia thuiella) and the citrus leafminer (Phyllocnistis citrella.) Once an adult lays its eggs, they hatch and work their way into the leaf tissue where they feed. The damage can range from leaf curling to leaves with trails in them. Contact pesticides do not typically work in these cases because the larva is inside the leaf. Unless you are targeting exposed adults, you will need a systemic product.
Borers. Often we think of borers only as beetles. However, some can also be caterpillars, such as the Eastern pine shoot borer (a.k.a. white pine tip moth) (Eucosma gloriole); banana moth (Opogona sp.); and the lesser peachtree borer (Synanthedon pictipes). These caterpillars have some major mandibles, enabling them to chew their way through the trees, twigs and branches. After feeding on their respective hosts, they will pupate and emerge as flying adults. The adults use their flying abilities to find hosts for their young. Treating for borers can be more complicated than other pests and will require proper timing of pesticide applications. This is one reason positive identification is so important.
Control options
For the average foliar-feeding caterpillar there is an array of spray products available. One of the keys is to not wait until the caterpillars are large and getting ready to pupate. You need to target them while they are smaller and more susceptible to insecticides. One of the more commonly used products is Bt or Bacillus thuringiensis. When using this product it is important to understand that it must be ingested by the caterpillar. This will cause the caterpillar to stop feeding, but it may still live for a few days. It is a common mistake to think the product is not working in the first few days. The most commonly used variety of Bt for caterpillars is B.t. var. kurstaki (Btk), which is host-specific to caterpillars. There are other Bt products on the market but they target other pests such as flies and caterpillars. A great side benefit to Bt is its compatibility with a biological control program. Bt is also approved for use in organic growing operations.
There are many other spray products out there that are labeled for caterpillars, but tend to be more broad spectrum, including Sevin, Azatin, Molt-X, Pedestal, Orthene, Conserve and insecticidal soap.
When it comes to borers, control methods need to be approached a little differently. Borers are harder to control because once they move under the bark, it is hard to target them with traditional pesticides. The best way to approach borers is prevention. There is often a stress factor for the plants involved that allows borers to move in such as improper irrigation or improper nutritional practices. If treatment is needed, try to time the applications when the borers are the most vulnerable—the egg or early larval stage. Pesticides that contain a synthetic pyrethroid work best on these young life stages. There are also commercial monitoring traps available to capture the adults of these pests, which will help you better target your pesticide applications. Check with Ag-Bio (www.agbio-inc.com) for list of available traps.
Biological control
There are only a few commercially available bio control agents. One is the parasitic wasp Trichogramma, which attacks more than 200 kinds of caterpillar eggs by laying its egg inside of the caterpillar’s egg. There are several species of Trichogramma available, so talk to a reputable supplier to find out which one is right for you. Also remember many of your native beneficials can help, including ladybird beetles, green lacewings and flies.
Beneficial nematodes are gaining momentum as a good bio control. These can work very well on some species of caterpillars. An important caveat—the caterpillar must spend part of their life cycle in the soil or live near the soil surface to be exposed to the nematodes. This is true for caterpillars like cutworms.
Some of the newest developments in controlling boring caterpillars with nematodes are being developed by USDA Agricultural Research Service entomologists David Shapiro-Ilan and Ted Cottrell. They are tank-mixing beneficial nematodes with a fire-retardant (Baracade Fire Gel), and applying it to trunks of infected trees. In the past, nematodes would dry out too quickly to be effective. The tank mix helps keep moisture on the tree trunks, allowing the viable nematodes time to come in direct contact with the pest. They have been doing research on lesser peachtree borers. They found that one springtime application of the beneficial nematode S. carpocapsae with Baracade provided 88 percent suppression on mature peachtree borers. Another study found that three applications in the fall during egg laying season suppressed all damage.
Caterpillars can be one of the easier pests to control. The key is to find them early and treat them early before they eat up all your profits.
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