Spruce webspinning sawfly

Distribution

Canada

This species occurs throughout the south and central interior of British Columbia; it also occurs east to Nova Scotia.

Micro-habitat(s)

Needle

Damage, symptoms and biology

Cephalcia fascipennis is a solitary web-spinning sawfly that occasionally causes noticeable damage to ornamental spruce trees or hedges. Outbreaks occasionally occur in seed orchards. Because spruce retain their needles for 5 or more years, it takes as long for a seriously damaged tree to regain its normal appearance.

Mature larva up to 20 mm long. Head, light tan with pair of seven segmented antennae and brown spotting over crown. Body, yellowish brown with reddish middorsal, midventral and spiracular stripes. There are a pair of jointed appendages at the posterior end.

This species overwinters as a prepupal larva in earthen cells. Adults emerge in spring or early summer. The female begins ovipositing on the day of emergence whether or not she is mated. Sex is determined by whether or not the egg is fertilized; unfertilized eggs produce males (parthenogenesis); and fertilized eggs produce females.

Each female can lay up to 23 eggs. Shining green cylindrical eggs are laid singly or end-to-end in rows of two to four on a needle. Eggs hatch in 18-24 days. On hatching, the larvae construct shelters from silk and frass at the crotch of a twig or branch. The larvae forage from these shelters by cutting the older needles and eating them from the base outward.

Tips of needles are not usually eaten and may be incorporated into shelters. The mature larvae drop to the soil from late July to August, burrow to a depth of 5-8 cm and construct earthen cells.

Main host(s)

Black spruce, Colorado spruce, red spruce, white spruce

Secondary host(s)

Balsam fir, red pine, Sitka spruce, tamarack