Conifer feeding sawflies in the genera Diprion and Neodiprion may feed on the foliage, mine buds, or bore into the pith of the shoots of their host plants. A few selected species are discussed in this guide, and may be distinguished from one another by their caterpillars and in some cases, host preferences. However, they may also overlap on the same hosts. Separate entries for the European pine sawfly (Neodiprion sertifer), introduced pine sawfly (Diprion similis), and redheaded pine sawfly (Neodiprion lecontei) are available in this guide. Here, the information is combined in case it makes comparison or differentiation of the species easier for the reader.
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.
The introduced pine sawfly (Diprion similis) was accidentally brought to parts of the United States, including New England, from Europe. The first record is from New Haven, Connecticut in 1914. Two generations per year are noted for the northern parts of its introduced range, with three occurring per year in North Carolina. In most of North America, overwintering is thought to be spent in the cocoon in a prepupal form. The emergence of first generation adults may begin in April, and continues through May and June. The adults of the second generation emerge from July to August. The first generation larvae may be present from May to August, and the second generation larvae from late July to early October. There is a great overlap in the generations, and throughout much of the growing season all life stages of the insect may be found on the trees at the same time, depending upon local variability. Eggs are laid in old host plant needles, and covered with a green, frothy substance. An average of 6-10 eggs are laid per needle, with each female laying on average 70 eggs total in her lifetime. Larvae are black or dark brown with two dark stripes on the back (dorsal side) and yellow and white markings on the side of the caterpillars. The head of the caterpillar is shiny black, and the underside is pale yellow or white. Caterpillars may reach up to 1 inch in length. There are 3 larval instars, the first of which feeds gregariously (in groups) but as caterpillars grow in size, they disperse and feed alone. Larvae feed for approximately 30-40 days, depending on temperatures. When it is time to pupate, cocoons are spun on host plant needles, at the ends of branches, and sometimes on the trunk in bark crevices. Some cocoons may enter diapause, which can last 4-5 weeks or in some studies, 1-3 years.
The redheaded pine sawfly (Neodiprion lecontei) 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, and 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.
The following describes damage from the European pine sawfly (Neodiprion sertifer): 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.
The following describes damage from the introduced pine sawfly (Diprion similis): Caterpillars feed on the needles of their hosts. Defoliation from these caterpillars may be most severe on the upper half of the host plant, however, entire trees may be defoliated in high populations. Young larvae feed together in groups, but larger (more mature) larvae will feed individually. Occasionally, some feeding has been reported on the bark of small branches (creating small pits). The introduced pine sawfly overlaps on some of the same hosts as the European pine sawfly and the redheaded pine sawfly (see host comparisons above).
The following describes damage from the redheaded pine sawfly (Neodiprion lecontei): 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. Slash pine (Pinus elliottii) is also a host of the redheaded pine sawfly, but is found in the southeastern United States.
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. Monitor for introduced pine sawfly caterpillar feeding beginning in May, however historically in Massachusetts reports of feeding may not increase until late June in some locations (Bob Childs, Personal Communication). 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 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 redheaded pine sawfly caterpillar activity visually on susceptible ornamental plantings in the spring and early summer before feeding becomes extensive in the fall.
Remove European pine sawfly caterpillars 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 European pine sawfly has historically been a problem. Introduced pine sawfly caterpillars may also be handpicked and destroyed by dropping them into a bucket of soapy water, particularly when caterpillars are young and still feeding gregariously. Austrian pine (Pinus nigra) may be somewhat resistant to the feeding of the introduced pine sawfly. It can also be effective on individual, ornamental specimens to hand pick and destroy clusters of redheaded pine sawfly caterpillars to reduce feeding.
Each of these sawfly species has different natural enemies or biological control options. The European pine sawfly 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.
Coppel et al. (1974) summarized North American records of natural enemies of the introduced pine sawfly, and noted 35 species. Four of the five most important parasitoid species listed were probably of European origin and may have been accidentally introduced. The most effective species noted is the chalcid wasp pupal parasitoid, Monodontomerus dentipes, and the ichneumonid wasp larval parasitoid Exenterus amictorius (Invasive Species Compendium; CABI). Abiotic conditions are important mortality factors for second generation caterpillars as well. Cold winter temperatures may kill up to 50% of second generation caterpillars before they reach the cocoon (pupal) stage.
Lastly, rodents are important predators of redheaded pine sawfly 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 (larvae) (NL)
Azadirachtin (NL)
Bifenthrin (NL)
Carbaryl (L)
Chlorpyrifos (N)
Cyfluthrin (larvae) (NL)
Deltamethrin (larvae) (L)
Emamectin benzoate (L)
Flonicamid+cyclaniliprole (N)
Gamma-cyhalothrin (L)
Horticultural oil (larvae) (L)
Imidacloprid (larvae) (L)
Indoxacarb (L)
Insecticidal soap (larvae) (NL)
Lambda-cyhalothrin (L)
Permethrin (L)
Spinetoram+sulfoxaflor (N)
Spinosad (NL)
Note that the active ingredients included in the above list are suitable for sawflies, but that it may be helpful to check the individual entries for each of these species of conifer feeding sawfly elsewhere in this guide. Management options specific to each individual insect may be searched using the insect scientific name.
Active ingredients that may be applied systemically include: acephate (injection), acetamiprid (injection), azadirachtin (injection, soil drench), emamectin benzoate (injection), and imidacloprid (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.
