Spruce needle miner
Black, Colorado, Engelmann, Norway and White spruce
Appearance and Life Cycle
The adult stage of the insect is a small, dark brown moth, with a wingspan of 11-15 millimetres (mm). The forewings are dark brown with three broken, greyish-white bands. The hind wings are a lighter brown; with a light coloured outer fringe. Adults may be present from mid-May to early July. Females deposit their eggs in a single row, in groups of 2-12, on the underside of the needles. The eggs are round, ridged, flattened and may be pale yellow to pale green in colour. The larvae hatch in 10-14 days and feed as a group at the base of old needles. Newly hatched larvae are yellow at first, changing to a pale green with light brown heads. The larvae overwinter in nests constructed of frass and dried, mined needles tied together with fine silk. In spring, the full grown larvae are approximately 8 mm long with light green bodies and brown heads. The larvae pupate in cocoons within the nests, emerging as adults, completing their single generation a year life cycle.
Larvae cause damage by entering the needles and devouring the entire contents. Feeding by spruce needle miners will not kill trees, but the reduced growth and nests often makes trees look unsightly. Young trees growing under adverse conditions are particularly susceptible and an infestation could result in serious injury.
Several species of parasites attack spruce needle miners which generally keeps the pest under control. When only a few trees are infested, the nests can be hand picked or washed from the trees in early spring before the buds swell or in late fall. Chemical control can be achieved in mid and late June by spraying with carbaryl or malathion with sufficient pressure to penetrate the nests. Dimethoate applied to foliage in early June or late August will also provide control.
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