Description
Caterpillars are the larval form of moths and butterflies and reside in the order Lepidoptera. They are also known as cutworms, hornworms, borers, loopers, codling moths and leafrollers. Caterpillars are voracious feeders and use their chewing mouthparts to feed on flowers, fruit and foliage. Adults feed on pollen and nectar. Caterpillars are problematic on outdoor crops but can also find their way into greenhouses to feed on ornamentals and more.
Target Crops
Because of the wide variety of caterpillars, the crops they attack are diverse. They are often named for their preferred host plants. Cabbage worms and diamond back moths feed on cole crops (cabbage and kale). Hornworms feed on tobacco, tomato, eggplant, peppers and potato. Armyworms prefer grains and cereals. The beet armyworm attacks many types of vegetables including beans, beets, tomatoes, lettuce, onions and peas. Corn borers eat corn, grains, sugarcane and other grass crops. European corn borer may feed on Chrysanthemum, Dahlia, Heliopsis and Leucanthemum. These flowers are especially susceptible if grown near cornfields.
Life Cycle
Caterpillars go through complete metamorphosis, where the larval form is quite different from the adult. Eggs hatch into a larva or caterpillar which transitions in the pupal stage to an adult. Adult female moths lay between 20 to 100 eggs underneath the leaf surface. The juvenile caterpillars eat plant foliage as the instars increase in size over 7 to 10 days. Pupation often occurs with caterpillars spinning cocoons attached to plant surfaces and the adult emerging after approximately one week. The entire life cycle from egg to adult occurs in about 3-4 weeks, depending on temperature.
Beneficial Insect Control
Trichogramma—This tiny parasitic wasp attacks over 150 species of moth eggs. Can be used in the greenhouse as well as in orchards. Rates are 2/ft² weekly or 100,000-300,000/acre.
Brown and Green lacewing larvae—these top generalist predators attack eggs and juvenile stages of most soft bodied pests. Rates for the green lacewing, Chrysoperla, larvae are 1-5 larvae/ft² on hot spots and 1/ft². elsewhere, weekly. For the brown lacewing, Micromus, 1-3/10ft² adults.
Dicyphus hesperus-- is a predatory bug and will feed on moth eggs (it is often used to target whitefly). It is best suited for use with vegetable crops as it will also feed on plants. Release early in the season at a rate of .25-.5/10ft². Repeat in 2-3 weeks.
Insecticide Options
- Dipel and Javelin are both contact insecticides containing Bacillus thuringiensis spp. kurstaki (Btk). Bt acts as a stomach poison and after consuming it the caterpillars usually die in 3 to 4 days.
- Azadiractin or neem oils act as insect growth regulators, antifeedants and ovipositional deterrents. These include AzaGuard and Molt-X.
- For a quick knockdown, use Pyganic with Pyrethrin, made with botanically-derived active ingredients. It has a lower impact on the environment with a high impact on pests.
- Mycoinsecticides containing entomopathogenic fungal spores also work well. These include Botanigard, Mycotrol,NoFly and PFR 97 and LalGuard M-52 OD.
Cultural Control Tips
- When scouting for caterpillars look for fecal droppings or insect frass on the damaged leaves and remove caterpillars by hand. Drop into a bucket of soapy water.
- Check with your local extension office for more information on particularly destructive pests in your state, such as Asian gypsy moth or tent caterpillars.
- Tent caterpillars on trees and shrubs can be pruned out before eggs hatch or removed with a high-pressure jet of water.
- To stop moths from laying eggs on plants, cover with a screen, mesh or cage.
- Till soil after harvest to reduce chance of pupae surviving in the soil for certain species.
- Plant a ‘trap crop’ to lure caterpillars away from desirable plants.
- Use native plants and flowers to attract natural enemies, like insects, spiders and birds that eat caterpillars.
- Use pheromone traps and lures to catch adult moths before they can lay eggs.
Remember that many caterpillars change into important pollinators, beautiful butterflies and provide a food source for songbirds. Consider planting host plants for these attractive species.
Research by Doug Tallamy suggests that during the breeding season, birds often rely heavily on caterpillars as a primary food source for their nestlings. Studies have found that a single pair of Carolina Chickadees can feed their nestlings with approximately 6,000 to 9,000 caterpillars during a breeding season. Other songbird species, such as warblers, vireos, and thrushes, also have high caterpillar demands to ensure the survival and successful fledging of their young.
Monarch butterfly caterpillar
Resources
Controlling Caterpillars, Greenhouse Management 2020
Caterpillar Pests, Dr. Raymond Cloyd, GPN, 2001
Controlling Caterpillars in the Garden, OSU Extension 2020
A Case for Caterpillars, Penn State Extension 2021
A Key to Common Caterpillar Pests of Vegetables, Texas A&M Extension 2011
Doug Tallamy’s Impact, Caterpillar and Bird Diversity
