|scientific name Pikonema alaskensis |
common name Yellowheaded Spruce Sawfly
Boreal forest, urban forests, shelterbelts.
Adults emerge late May to mid June; larvae feed through June and July.
Adult: Adults are brightly colored wasp-like insects (four membraneous wings with hind wing smaller than forewings, venation apparent, ovipositor well developed, legs have 5 segments) (Triplehorn and Johnson 2005: 481). The length of the forewing is shorter than that of the abdomen (Goulet 1992: 111). They are medium to small in size. Pikonema alaskensis antennae are long, segmented and covered with hair-like structures (setae). The clypeus, a hardened plate on lower part of face (Triplehorn and Johnson 2005: 782) is notched or indented. The body and head have a shiny surface with little or no markings. The inner tooth on tarsal claw is distant from and below apex of outer claw (Goulet 1992: 110; Ross 1937: 17). The pits from which the setae emerge on the head are not clearly outlined or raised above the surface (Goulet 1992: 110). The edges of the ovipositor are curved when viewed from the side, and it is almost twice as long as the cercus (Goulet 1992: 110). The abdomen of the female is chestnut coloured, but can vary to black. The saw terminates in a point. Males are always narrowly banded with rufous colour, which can merge to black (Ross, 17). Adults can be found on foliage looking for egg-laying sites or mates.
Larvae: Caterpillars are small (16 -20 mm) and cylindrical, but not tapered at apex (Ross 1937: 17). The have a yellowish brown head, with shiny olive green bodies and two gray green lines along back and sides. (Ives and Wong 1988: 33). There are no crotchets, or hooks, on the prolegs. The eyes are a single pair of ocelli (Triplehorn and Johnson 2005: 481). Larvae can be found feeding externally on foliage and are seen much more often that adults.
Adults emerge from cocoons late May early June, coinciding with new growth flush on spruce trees. The female seeks a male, then deposits fertilized eggs singly on new growth. The larvae hatch in 1 to 2 weeks, and reach maturity in 3 to 8 weeks. They dine externally on the new growth of spruce trees, then move on to the old growth. This often leaves the twigs and twiglets of spruce trees looking bare. The larvae then drop into soil where they overwinter in a cocoon covered in leaf litter and soil particles. They will then pupate in spring. The yellowheaded spruce sawfly produces only one generation annually. (Philip and Mengersen 1989: 60).They are considered a serious pest of spruce trees, and do considerable damage to nursery crops and urban trees. The evidence of their activity can be readily seen on many urban spruce trees.
A common species in Alberta; often viewed as a pest. Damage to urban and nursery spruce can be moderate to severe.
The larvae feed on new foliage of spruce (Picea), especially Engelmann, white, black, and blue spruce. They can also be found on ornamentals and shelterbelt spruce (Ives and Wong 1988: 33).
Pikonema alaskensis is common across Alberta (Philip 1975: 46), native to North America (Philip and Mengersen, 60)
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