“Caterpillar” is the common name for the larvae of members of the order Lepidoptera (the insect order comprising butterflies and moths). Caterpillars generally eat leaves but some species, such as Codling Moth and Budworms feed inside fruit. Common pests in this group include Tobacco hornworm, Cabbage white butterfly, Cluster caterpillar, Cabbage moth, Grapevine moth, Loopers, Light brown apple moth and Lawn armyworm.
Tree-boring caterpillars mature to become part of a group called clear-winged moths, which look similar to wasps. These moths lay eggs in late spring. When the resulting caterpillars hatch, they most often find an entry way into a tree through a wound, crack or graft scar.
Caterpillars damage plants by chewing on flowers, leaves, shoots and fruit, and can also bore into wood. Tree-boring caterpillars damage and stress a tree by feeding on the inner bark and cambium tree layer. A large enough population will kill the tree.
A caterpillar is the larval stage of butterflies and moths.
Caterpillars have a segmented body consisting of a head, a thorax (with three pairs of jointed legs with hooks), and an abdomen (usually with five pairs of stumpy prolegs).
Many species of caterpillars begin the season as overwintered eggs. Other species overwinter as pupae in a chrysalis or cocoon.
The larval (caterpillar) stage usually lasts from about two weeks to a month, and is the longest life stage for many Lepidoptera (butterflies and moths). During this stage, the caterpillar can grow in size more than 30,000 times.
Look for feeding holes, excrement, webbed or rolled leaves, caterpillars, and eggs.
If parasite introductions are planned, put out pheromone traps for adults (late winter through early summer) to identify the species of egg-laying moths and to time Trichogramma releases.
Use a degree day calculator to find out when the moths are in flight.
Most caterpillars have several species of parasitic wasps or flies that attack them. Look for parasite cocoons next to caterpillars, darkened caterpillar eggs, or exit holes in dead caterpillars. Other general predators include birds, assassin bugs, lacewings, predaceous ground beetles, and spiders.Naturally occurring diseases caused by viruses, bacteria, or fungi often kill caterpillars.
As with any pest, a combination of biological and cultural controls, compatible chemicals and preventive measures gives the best result.
‘Tricogramma’ (T. platneri, T. pretiosum, T. minutum, T.brassicae): Trichogramma destroy eggs of over 200 pest moth species including cutworms, fruit worms, leaf worms, leafrollers, loopers, armyworms, and borers. These pale yellow micro-wasps, 1/100 inch long, smaller than a pinhead, drill through moth eggs to deposit 1-3 of their own eggs. Trichogramma larvae eat out the insides of pest eggs, pupate, and cut an exit hole in moth eggshells for winged adults to squeeze through. Males emerge first, wait for females, and immediately mate. The life cycle from egg to adult is completed in 7 to 10 days (longer in cool weather). This short life cycle allows as many as 30 generations per season, and rapid population increase. Hence, early season releases produce large populations positioned to fight pest invasions.
‘Green Lacewing’: The larvae of green lacewing are voracious general predators, devouring any soft-bodied arthropod they can overcome, including most caterpillar (worm) pests (armyworms, budworms, bollworms, borers, corn earworms, cabbage loopers, codling moths, etc.), aphids and other pests. The grayish-brown larvae resemble miniature alligators, and are 3/8 inch long when full-grown. Larvae search out pests, and use their pincer-like jaws to seize, inject digestive enzymes, and suck juices out of pests. Interfering ants, waxy coatings or hard shells on pests and low temperatures deter lacewings from dining on and destroying pests.
‘Podisus’ or ‘Spined Soldier Bug’: Podisus are aggressive, voracious true bugs which kill caterpillars and beetle grubs. They attack prey during all larval stages and as adults. They can kill much larger prey by piercing the caterpillar with their mouth parts, injecting digestive enzymes, then sucking up the partially digested insides. Podisus has a long life cycle and will take several months to become established so other biological controls should be used along with it at recommended rates.
‘Orius’ or ‘Minute Pirate Bug’: Orius are generalist predators that consume a variety of pests including small caterpillars, mites, aphids, and thrips. They are most effective for pests with life stages that inhabit flowers (such as flower thrips). Orius pierces its prey with its mouth parts and sucks out the body fluids. If prey is abundant, Orius kills more thrips than it needs to survive. The presence of pollen favors development of Orius as it acts as an alternate food source. Both adults and nymphs are active predators.
Other measures Use insecticides only when damage is becoming intolerable, nonchemical methods haven’t worked and smaller caterpillars are present. Avoid insecticides that can kill beneficial insects, and don’t treat butterfly garden plants, because you’ll kill the caterpillars that will become butterflies.
- Bacillus thuringiensis subspecies kurstaki (Btk) (Dipel DF) is a microbial insecticide that kills only caterpillars. It’s safe to use near bees, beneficial insects, and wildlife. Caterpillars must feed on treated leaves to be affected. Because it’s most effective on small, newly hatched caterpillars and breaks down rapidly, treatment timing is critical.
- Spinosad (Entrust, Monterey Garden Insect Spray) is a safe microbial-based insecticide but it can have some negative impacts on beneficial insects.
- Beauveria bassiana (BotaniGard, Mycotrol O) is a biological insecticide that can be used alone or in a tank mix with Bacillusthuringiensis (vars. kurstaki, aizawai) to control diamondback moth, imported cabbage worm, and cabbage looper. The tank mix provides control of later instars (3 rd to 4 th) and aids in suppressing resistant populations.