The pine false webworm is an introduced species from Europe that was first detected in Pennsylvania in 1925, but is now widely distributed through the northeast. It is considered to be a very common web-spinning sawfly and defoliator of the aforementioned host plants. The prepupae may overwinter in cocoons in earthen cells they create 5-8 cm beneath the soil surface. In the spring, adults emerge roughly between mid-April and mid-May. Females lay their eggs end-to-end on 1 year old needles in groups of 3-10. A small slit is made in the needle, and part of the egg is embedded in it upon oviposition. On average, each female can lay up to 16 eggs. Eggs hatch and tiny larvae spin loose webs near the base of host plant needles. Several larvae may be found feeding in each web, and feed by cutting up the needles and tangling them in their webs. This sawfly caterpillar possesses no abdominal prolegs (some sawfly caterpillars have 0 fleshy prolegs and some have 6 or more pairs) and very short hardened thoracic legs. This makes it difficult for them to crawl around the host plant. Caterpillars are greenish in color with purple-ish stripes and a light brown head capsule that has two antennae. Caterpillars feed for approximately 18-20 days. Older caterpillars may eventually feed singly from webbing tubes attached to host plant branches. A single generation is reported per year.
Can create unsightly webs and much defoliation where host plants have defoliated twigs, stems, and branches that are coated with webbing. Webbing is full of frass (excrement). Often, new growth is not fed upon by this insect, but older needles are completely stripped from the tree. In these cases, new growth may die without having been fed directly upon, due to the stress caused to the host plant. Webbing may appear as tubes on branches or twigs. The pine false webworm can be a significant pest in forestry and plantation situations. Management specific to pine plantations is not discussed here. Individual specimen trees in ornamental landscapes may be managed using the suggestions listed here. Consecutive years of defoliation of over 70% of the host plant may lead to whole tree mortality. Pines may be susceptible to secondary pest invasion following defoliation by pine false webworm, including bark beetles or fungal diseases.
A sex pheromone of the pine false webworm female sawfly has been identified that will attract male adult sawflies in the field. This pheromone could potentially be used with traps to help monitor for these insects (Staples et al., 2009).
Small infestations can be pruned away, with infested branches clipped out and destroyed.
A tachinid fly parasitoid of the pine false webworm was released from its native European range into Ontario for the biological control of this insect. European species, Myxexoristops hertingi, a larval parasitoid and the ichneumonid Xenoschesis sp. (larval parasitoid) and the egg parasitoid, Trichogramma sp., were also studied as potential biological control agents of the pine false webworm in North America (Kenis and Kloosterman, 1999). Certain bird species and rodents may also be predators of this insect.
Acephate (NL)
Azadirachtin (NL)
Bifenthrin (NL)
Carbaryl (L)
Chlorpyrifos (N)
Cyfluthrin (NL)
Deltamethrin (L)
Dinotefuran (NL)
Flonicamid+cyclaniliprole (N)
Gamma-cyhalothrin (L)
Horticultural oil (L)
Imidacloprid (L)
Insecticidal soap (NL)
Lambda-cyhalothrin (L)
Pyrethrins+piperonyl butoxide (L)
Pyrethrin+sulfur (NL)
Spinetoram+sulfoxaflor (N)
Spinosad (NL)
Contact insecticides may not reach the caterpillars if they are feeding within their webs, so if selecting those active ingredients, they would need to be forcefully sprayed through the webs to reach the insects. Low doses of carbaryl and permethrin have been found to be effective in killing the larvae (Lyons et al., 1993). Low-volume aerial application of azadirachtin-based insecticides have been studied in semi-mature and mature red pine plantations and good management of pine false webworm larvae was found (Thompson et al., 2003).
To entomologists, the term caterpillar refers to the immature or larval life stage of the Lepidoptera - butterflies and moths. However, the public and some entomologists included sometimes use this term interchangeably to refer to the immature or larval life stage of certain Hymenoptera - in particular, sawflies.
This can cause confusion when selecting management options for pests collectively referred to as caterpillars. The larvae discussed here will mature into an adult sawfly. This means that the active ingredient Bacillus thuringiensis Kurstaki (Btk) will not be effective at managing this insect. Btk will only kill the caterpillars of moth (or butterfly) pest insects. It will not kill sawfly larvae.
Sawfly larvae can be distinguished from moth or butterfly caterpillars by the presence of or absence of 6 or more prolegs. Some sawfly species will have 6 or more pairs of fleshy abdominal prolegs, whereas some sawfly larvae will have 0 pairs of fleshy abdominal prolegs. Caterpillars that mature into butterflies or moths will have 5 or fewer pairs of fleshy abdominal prolegs. Prolegs are soft, and found behind the hardened 3 pairs of thoracic legs on the insect. In butterfly or moth caterpillars, the prolegs will also have tiny hooks or crochets on the very bottom.
Active ingredients that may be applied systemically include: acephate (injection), and azadirachtin (injection, soil drench).
When used in a nursery setting, chlorpyrifos is for quarantine use only.
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.
