At minimum, 17 different species of sawfly may be found feeding on various pine species (Pinus spp.). The European pine sawfly (Neodiprion sertifer) is noted here as this insect is a native of Europe and was accidentally introduced into the US around 1925. It is now widespread and invasive in New England. Mature larvae are gray-green, 0.7-1 inch long caterpillars. They have 3 pairs of thoracic legs and 7 pairs of fleshy abdominal prolegs. Mature larvae also have shiny black heads and five stripes that run parallel along the length of their bodies. Stripes vary in color, from dark green or black to gray-green, with a light green stripe running directly along the middle of the back of mature larvae. Eggs are laid evenly spaced along pine needles, looking like rows of light brown spots. Adult European pine sawflies are wasplike, brown or black in color, and approximately 0.4 to 0.5 inches in length. Females are active in September and October and lay their eggs in slits they cut in pine needles using sawlike ovipositors (egg laying structures). They prefer current year's needles for egg laying. Females typically lay eggs in groups of 6-8 in a single needle and repeat this at least 10-12 times, laying approximately 60-96 eggs per female (a range of 30-140 eggs per female is reported in the literature). The egg stage overwinters, and only one generation occurs per year. Egg hatch may occur roughly between late-April and early May, with larvae feeding on previous year's needles until approximately late-May or early June, at which time they drop to the ground to pupate. By late-August, following a summer diapause, pupation has occurred and adults emerge in September.
Needles may appear dry and straw-like from the feeding activity of young larvae, who eat the surface of the needle. Older larvae may eat entire needles from their tip to the base. Aesthetic damage may be most apparent on mugo pine in landscapes and nurseries. Since larvae rarely attack new foliage and most trees are seldomly entirely defoliated, host plants typically survive the activity of this insect. On occasion, larvae may also feed on the bark of new shoots causing shoot deformation and twig mortality. However, this pest is not typically considered a serious threat to the overall health of a tree. Compare with the redheaded pine sawfly and introduced pine sawfly.
Monitor for the presence of European pine sawfly eggs in the needles between September (current season's) and mid-April (previous season's). By late April and early May, begin to look for dry, straw-like needles on the previous year's growth. This is a sign that young larvae might be feeding and if that is the case, it is a great time to try to manage this insect.
Remove larvae by pruning infested branches if this is practical. Otherwise, remove and dispose of clusters of caterpillars with a gloved hand. Northern cultivars of Scots pine are known to be more resistant to attack than southern ones, so selectively plant those cultivars in areas where this insect has historically been a problem.
N. sertifer is attacked by several hymenopteran and dipteran parasitoids, and many predators including ants, bugs, beetles, lacewings, spiders, small mammals and birds. Pathogenic fungi, bacteria, and a species-specific nuclear polyhedrosis virus also attack it. The species of natural enemies involved depends upon which portion of this insect's native or introduced range is being considered. A lethal species-specific nuclear polyhedrosis virus frequently infects caterpillars of the European pine sawfly. The disease is caused by Borrelinavirus diprionis (NeseNPV). It is often one of the main factors causing the abrupt collapse of outbreaks of this species, with larvae becoming infected either by ingesting the virus with food, or via an infected parent.
Larvae of this species also have a special defense strategy against predators and parasitoids, including by being found in the environment in groups. The larvae will perform alarm reactions and defensive displays, including "U-bending", jerking, and stretching. European pine sawfly caterpillars will also regurgitate a droplet of resinous liquid when harrassed. This behavior has been shown to repel ants, other predaceous insects, spiders, and birds, as well as parasitoids.
Acephate (NL)
Azadirachtin (eggs) (NL)
Bifenthrin+imidacloprid (L)
Carbaryl (L)
Chlorpyrifos (N)
Cyfluthrin (NL)
Deltamethrin (L)
Dinotefuran (NL)
Flonicamid+cyclaniliprole (N)
Gamma-cyhalothrin (L)
Horticultural oil (L)
Imidacloprid (L)
Indoxacarb (L)
Insecticidal soap (NL)
Lambda cyhalothrin (L)
Pyrethrin+sulfur (NL)
Spinetoram+sulfoxaflor (N)
Spinosad (NL)
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), azadirachtin (injection, soil drench), dinotefuran (soil drench), and imidacloprid (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.
