Monoctenus

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Taxonomy

Family: Diprionidae
Family common name: conifer sawflies
Subfamily: Monocteninae
Genus: Monoctenus Dahlbom, 1835
Subgenera: none

Background

The Diprionidae are known as the conifer sawflies, though they are not the only family to use conifer trees as host (others include Siricidae, Pamphiliidae, Xyelidae, some genera of Tenthredinidae). Many are destructive pests as larvae, and so their biology has been more extensively studied than some other groups. Diprionids have stout bodies and distinctive antennal characteristics that make adults easy to recognize (Furniss and Carolin 1977).

Monoctenus is unique in the Diprionidae by using juniper trees as host. They are uncommonly observed, and, unlike closely related genera, seldom cause significant damage to their host (Rose et al. 2000).

Diversity

There are 13 described species worldwide, restricted to the Northern Hemisphere. Five species occur in North America (Taeger et al. 2010, Smith et al. 2010).

Diagnostic characteristics

• pronotum strongly constricted medially, as seen from above (Goulet 1992)
• head closely appressed to thorax, no distinct “neck” (Goulet 1992)
• antennae serrate in females, unipectinate in males (Smith 1974b, Goulet 1992)
• ocelli arranged in almost a straight line as seen from above (Goulet 1992)
• vein 1A and 2A of fore wing fused in the center, making two distinct anal cells without a crossvein (Goulet 1992)
• clypeus about truncate, not emarginated (Smith 1974b)
• fore wing vein M meeting Sc+R just basal to the junction of Rs+M and Sc+R (Smith 1974b)
• area between antennal segments and clypeus convex (Smith 1974b, Goulet 1992)

May be confused with

Diprionidae are most easily recognized by the distinctive antennae of both sexes, but also are characterized by small, stout bodies. The subfamily Monocteninae can be separated from the Diprioninae (Diprion, Gilpinia, Neodiprion, Zadiprion) by the singular comb-like projection from each antennal segment, and by the fused veins 1A and 2A in the fore wing. It can be separated from Augomonoctenus by the truncate clypeus and the fore wing venation (Smith 1974b, Goulet 1992).

Exotic pest species of concern

none

Host associations

Larvae in North America feed on trees of Cupressaceae. Most species feed on species of Juniperus (juniper), and a few also feed on Thuja occidentalis (eastern white cedar) and possibly other Thuja sp. (Smith 1974b, Goulet 1992, Smith et al. 2010).

Life history

The biology of many species is unknown. Monoctenus fulvus females lay one egg at a time into the scale-like leaves of their host. After hatching, larvae feed on the foliage, usually at the new growing tips. Larvae are longitudinally striped and measure about 30 mm at maturity. When disturbed, larvae will rear up the head and thorax, similar to other Diprionidae. Mature larvae will drop to the ground and burrow into the soil to overwinter and pupate. Monoctenus are univoltine (Marlatt 1886, Smith et al. 2010). Phenology is variable (Smith et al. 2010).

Distribution

World: Species are recorded from North America, in Europe, and in Japan (Smith 1974, Taeger et al. 2010).

North America: Monoctenus has two distinct ranges in North America. Three species occur in the east of Canada and the United States, from Quebec as far south as Virginia, west to Oklahoma; two species occur in central Mexico, one recorded in Durango, one recorded in San Luis Potosí (Smith 1974b, Smith et al. 2010b).

Map data from: GBIF.org (26 June 2019) GBIF Occurrence Download Monoctenus

Details about data used for maps can be found here.