The pine webworm is a Lepidopteran (moth) pest of ornamental pines and Christmas trees. A single generation occurs per year in the northern geographic range of this insect. Two generations are possible per year in more southern locations (Virginia to Florida), and even three may occur in some locations in Florida (Hertel and Benjamin, 1979). The larval stage is the overwintering life stage, found within the soil in a cocoon. Pupation occurs in the spring and adult moths may first be seen in June. However, adult emergence may be seen from June and July and even possibly into the beginning of August. Female moths lay their eggs in single rows along pine needles. Eggs are tiny and a single needle may hold up to 20 eggs. Eggs hatch and the tiny caterpillars (larvae) spin loose webbing around clusters of needles. Eventually, they pick a needle and begin their feeding as needle miners. Once too large, they stop mining the needles and feed within their loosely webbed, messy nests made of frass and silk. Up to 78 caterpillars can be found in a single nest, however some may only contain a couple caterpillars. In the northern parts of this insect's range, webs are found from late June through July. Webs may be approximately between 2-6 inches in length. Caterpillars continue feeding on the needles within the webs and brown, oblong frass pellets fill them. Fully grown caterpillars are 0.6 inches long, yellowish brown with darker brown stripes and may be present from August to October. By late September, caterpillars crawl or drop from their nests to the soil to form a cocoon within which they overwinter.
The pine webworm is usually considered to be a pest on seedling pines in plantations and managed landscapes. Webs are formed on the terminal twigs of the host plant, containing larvae, dead needles, and large amounts of brown frass by late June through July. The loosely constructed webs can be unsightly and typically the insect is not noticed until the feeding damage has been done and caterpillars are gone from their webs. Slash pine (Pinus elliottii) is also a host of the pine webworm, but is found in the southeastern United States.
Adult moths are attracted to lights (such as mercury vapor lights, historically) and may be light trapped at night. The webs/nests created by the caterpillars may be relatively easy to spot on host plant shoots. On pitch pine, the webs or nests may be found mostly near ground-level (Maier et al., 2011).
Webs made by these caterpillars can be hand picked or pruned out of the hosts and destroyed. If caterpillars are present within, this may help reduce the population of the insect on a single tree. However, removing empty nests (after caterpillars move to the ground to prepare their cocoons) will not reduce the number of insects on a single tree - but may improve aesthetic appearance.
Natural enemies of the pine webworm exist. Parasitic wasps and flies act as parasitoids, and certain species of native birds (chickadees and nuthatches) may feed on pine webworm caterpillars as well, after ripping apart their nests. Syzeuctus elegans, an ichneumonid wasp parasitoid, is a natural enemy of the pine webworm that is thought to be relatively common (Van Driesche et al., 2013). Eufrontina spp. are considered a relatively common dipteran (true fly) parasite of the pine webworm (Hertel and Benjamin, 1979). Additional reported natural enemies include but are not limited to: Sympiesis spp., Derostenus silvia, Apanteles spp., Phorocera tortricis, Trachysphyrus albitarsis, Mesostenus thoracicus, and Zaleptoygus spp. Predators include Acholla multispinosa as well as certain species of spiders (Wallesz and Benjamin, 1960).
Acephate (NL)
Azadirachtin (NL)
Bacillus thuringiensis subsp. kurstaki (NL)
Bifenthrin (NL)
Carbaryl (L)
Cyfluthrin (NL)
Deltamethrin (L)
Flonicamid+cyclaniliprole (N)
Horticultural oil (eggs) (L)
Indoxacarb (L)
Malathion (L)
Permethrin (L)
Pyrethrins+piperonyl butoxide (L)
Trichlorfon (L)
Active ingredients that may be applied systemically include: Acephate (injection) and azadirachtin (injection, soil drench).
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
