The redheaded pine sawfly is a native insect that can be an important pest of ornamental and forest pines. The prepupal stage overwinters in the leaf litter beneath or near host trees in a cocoon that is 1/2 inch long and reddish-brown and paper-like. Pupation occurs in the spring and adult sawflies emerge shortly thereafter. Adult sawflies are broad-waisted, possess two pairs of wings, 1/3 inch in length, with females being larger than males. Females have reddish brown heads and mostly black bodies. Females will lay approximately 100 oval, shiny, white eggs in rows on several host plant needles, creating slits in the needles to insert their eggs. Adult females are capable of laying viable eggs without fertilization from a male; however, those eggs will all be male young. Fertilized eggs will produce both male and female young. Eggs hatch within approximately 1 month and caterpillars (larvae) feed in groups. Early instar (younger) caterpillars have brown head capsules and white bodies. As the caterpillars mature, they grow to an inch in length, with red/brown heads and yellow to yellow-green bodies interrupted by 4-8 rows of black spots along the length of the body. Caterpillars have 3 pairs of hard, thoracic legs and 6-7 pairs of fleshy, abdominal prolegs. Feeding also happens over approximately the span of a month, with mature caterpillars dropping to the ground to spin the cocoons that will overwinter. Depending upon geographic locations, 1-3 generations may occur annually. The warmest locations may have up to 3 generations per year, with northern New England having a single generation per year. In southern New England and parts of New York, 2 generations per year are possible. This species is also capable of waiting multiple seasons to pupate. For example, some prepupae are able to wait until the second or third season before pupating. This strategy is useful for species survival. Another interesting survival mechanism of this species - disturbed caterpillars will lift their heads and rear-ends when threatened, and may even regurgitate to frighten off would-be predators. Additional sawfly species may be found on similar hosts, including but not limited to the European pine sawfly or introduced pine sawfly. For comparison, see the "pine sawfly" section of this guide.
Younger larvae feed on the outsides of the host plant needles. This results in shriveled, browned, and straw-like needles that remain attached to the hosts. Older caterpillars are capable of eating the entire needle. In certain parts of its range, the redheaded pine sawfly is capable of defoliating commercial pine stands, particularly during outbreak population years. Caterpillars will feed into the fall. Can be a very destructive defoliator of ornamental pines. During extended falls, or in milder climates (ex. Cape Cod), severe injury may occur in September and October. The caterpillars themselves may be vulnerable to extreme temperature fluctuations. Slash pine (Pinus elliottii) is also a host of the redheaded pine sawfly, but is found in the southeastern United States.
Traps and sex pheromones for monitoring redheaded pine sawfly populations are available. White cross-barrier or horizontal sticky traps have been studied in combination with pheromones in the literature (Anderbrant et al., 1989). Height of trap placement may be important in successfully monitoring for populations of this insect (Simandl and Anderbrant, 1993). Using traps to monitor for the redheaded pine sawfly may be more important in plantation grown trees. Monitor for caterpillar activity visually on susceptible ornamental plantings in the spring and early summer before feeding becomes extensive in the fall.
Because they feed in groups, caterpillars can be removed by hand from ornamental trees where they can be safely reached. They can then be destroyed or thrown into a bucket of soapy water. This can be an effective means of managing these insects on a single specimen tree.
Rodents are important predators of pupae. There are important diseases of redheaded pine sawfly caterpillars that also cause mortality in that life stage. Epizootics of polyhedrosis viruses can occur in redheaded pine sawfly populations. In fact, natural enemies (diseases, viruses, and predators of the redheaded pine sawfly) are abundant. Benjamin (1955) listed at least 46 hymenopteran and dipteran parasites of the redheaded pine sawfly. An introduced species of ichneumon wasp (Exenterus amictorius) is a parasite of the redheaded pine sawfly. Closterocerus cinctipennis is also an egg parasitoid of this species, along with the larval (caterpillar) parasitoid, Spathimeigenia spp.
Acephate (NL)
Azadirachtin (NL)
Bifenthrin (NL)
Carbaryl (L)
Chlorpyrifos (N)
Cyfluthrin (Larvae) (NL)
Deltamethrin (Larvae) (L)
Dinotefuran (Larvae) (NL)
Emamectin benzoate (L)
Flonicamid+cyclaniliprole (N)
Gamma-cyhalothrin (L)
Horticultural oil (Larvae) (L)
Imidacloprid (Larvae) (L)
Insecticidal soap (Larvae) (NL)
Lambda-cyhalothrin (L)
Permethrin (L)
Spinetoram+sulfoxaflor (Larvae) (N)
Spinosad (Larvae) (NL)
Younger caterpillars may be most vulnerable to chemical management options. Insecticidal soap may work best when used on the earlier instars rather than the older ones. Thorough wetting of needles if using contact insecticides needed.
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), emamectin benzoate (injection), 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.
