Diprion similis

Adults distinguished from other Diprionidae by antennae structure (bipectinate in males, serrate in females) and color pattern. The species can be separated from the native North American Neodiprion pinetum (also called 'white pine sawfly') by pheromone chemistry: D. similis uses the (2S,3R,7R)-propionate isomer, while N. pinetum uses the (2S,3S,7S)-acetate isomer. Larvae identified by black head capsule, gregarious feeding behavior, and characteristic longitudinal striping in later instars; the larval key in Davis et al. (2023) provides field identification tools.

Adult males measure 7–9 mm in length, entirely black with yellow legs except for brownish-black trochanters and femoral bases; antennae are black and bipectinate (feather-like). Adult females are slightly larger at 7.5–10 mm, with black head and thorax and variable abdominal coloration ranging from yellow and black to entirely dark; antennae are black and serrate (saw-like). Larvae possess black heads and caterpillar-like bodies: early instars are yellowish-green, while later instars develop black longitudinal stripes with yellow and white patches on a bluish-black background. Females have six larval instars, males have five.

Coniferous forests and plantations, particularly those containing Pinus strobus (white pine). In North America, occurs in mature white pine plantations and forest edges. Native range includes boreal and temperate pine forests of Europe and Asia.

Native to central and northern Europe (including Fennoscandia), Russian Siberia (to Lake Baikal), and China. Introduced to North America: first detected in Connecticut in 1914, now established throughout eastern United States and Canada wherever Pinus strobus occurs.

Two generations per year in most of range. Adults emerge in spring and remain active through summer; peak male flight in early June in Ontario. First-generation larvae present in early summer, with cocoons formed in July and adult emergence in August. Second-generation larvae appear in late summer, overwinter as prepupae in cocoons from autumn through spring, with some individuals entering extended diapause lasting up to three years.

Larvae feed exclusively on pine needles (folivory). In native range: Pinus sylvestris, P. mugo, P. cembra, P. sibirica, and introduced P. strobus and P. contorta. In North America: primarily Pinus strobus, also P. resinosa, P. banksiana, and P. sylvestris. Young larvae feed on needle edges, consuming partial tissue; older larvae consume entire needles.

• Pinus strobus - primary hostStrong preference in North America; traps baited with pheromone placed in white pine plantations
• Pinus sylvestris - hostNative range host and secondary host in North America
• Pinus resinosa - hostNorth American host
• Pinus banksiana - hostNorth American host
• Pinus mugo - hostNative range host
• Pinus cembra - hostNative range host
• Pinus sibirica - hostNative range host
• Pinus contorta - hostIntroduced species in native range

Holometabolous with two generations annually. Eggs laid in slits cut into pine needles by female's saw-like ovipositor, approximately 10 eggs per needle. Larvae pass through five (males) or six (females) instars, with early instars gregarious and later instars solitary. First-generation larvae pupate in silken cocoons on host tree, emerging as adults in approximately one month. Second-generation larvae descend to ground, spin cocoons, and overwinter as prepupae; pupation occurs in spring. Some individuals remain in extended prepupal diapause for up to three years. Adults are short-lived and do not feed.

Newly hatched larvae exhibit gregarious feeding, forming groups on host foliage; later instars become solitary. Larvae are diurnal feeders. Adults employ pheromone-mediated mate location: females release sex pheromone (propanoate ester of (2S,3R,7R)-3,7-dimethylpentadecan-2-ol) to attract males. Unmated females can produce viable male offspring through arrhenotokous parthenogenesis. Males are attracted to synthetic pheromone lures in field trapping; threo four-isomer blends are equally attractive as pure main component at matched release rates.

Larvae function as specialist herbivores and defoliators of pine canopies. In native range, populations are regulated by natural enemies including parasitoids and predators. In introduced North American range, populations have expanded with limited top-down control, leading to localized outbreaks capable of reducing tree growth rates and causing mortality. Serves as prey for birds and supports parasitoid communities where established.

Significant forest pest in North America, particularly in white pine plantations and ornamental plantings. Economic impacts include reduced timber growth, tree mortality, and costs of monitoring and management. Pheromone-based monitoring systems have been developed using the identified (2S,3R,7R)-propionate compound. Management options include manual removal of larvae, high-pressure water sprays for small infestations, and targeted insecticide applications for large outbreaks; natural enemy conservation is generally preferred.

• Neodiprion pinetumAlso feeds on white pine and shares common name 'white pine sawfly'; distinguished by pheromone chemistry (uses (2S,3S,7S)-acetate isomer), native to North America, and different larval coloration patterns
• Diprion piniEuropean conifer sawfly with overlapping native range; uses different pheromone component (propanoate of 3,7-dimethyltridecan-2-ol) that is not attractive to D. similis males
• Dermacentor similisUnrelated tick species described from western North America that shares the same specific epithet; no biological relationship but potential for nomenclatural confusion

The common name 'white pine sawfly' is ambiguous and confusing because it is applied to both D. similis (introduced, invasive) and Neodiprion pinetum (native North American species). The two species are not closely related and differ in pheromone chemistry, distribution, and management needs.

• invasive species
• forest pest
• parthenogenesis
• pheromone
• defoliator
• white pine
• Diprionidae
• Hymenoptera
• integrated pest management
• monitoring lure
• arrhenotoky
• gregarious larvae
• extended diapause

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Encyrtid Holdings | Entomology Research Museum
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• What's Eating Your Pine Needles? Sawflies, Probably
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• Bug Eric: Wasp Wednesday: Perilampid Wasps
• Sex Pheromone of the Introduced Pine Sawfly, Diprion similis, Revisited to Define a Useful Monitoring Lure: Deviating Chiral Composition and Behavioural Responses Compared to Earlier Reports.