Douglas-Fir Needle Midges
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Contents |
Hosts
Douglas-fir.
Distribution
Throughout host range.
Damage
Maggots (larvae) cause galls on current needles and can destroy most of the foliage if severely infected (fig. 109). Economic damage occurs in Christmas tree plantations. Needles fall off and, after consecutive years of defoliation, twig dieback can occur.
Identification
Noticeable galls may be seen on new needles starting in June (fig. 110). Galls of C pseudotsugae are swollen on the lower surface and colored on both surfaces with yellow, pink, or purple. C. constricts galls first appear as a patch of yellow discoloration with a dark purplish spot visible on both surfaces of the needle. After about 6 weeks the gall becomes dilated and flattened. C. cuniculator galls affect mainly the upper needle surface. The upper side is dirty yellow with a glossy, waxy appearance. Frequently needles are bent at site of injury. See Table 4 for comparison of needle midge damage with needle casts and adelgids.
There is one generation of these pests each year. Winter is passed as larvae in the soil. Adults appear in early May but are seldom noticed as they are small midges not much more than three-sixteenths inch long.
Similar damages
Look for needle 'galls" to identify. Rhabdocline needle cast, Swiss needle cast, Cooley spruce gall adelgid and, occasionally, aphids cause similar types of damage to Douglas-fir needles, but none of these produce galls.
References
From: Field Guide to Diseases and Insect Pests of Idaho and Montana Forests, USDA Forest Service Northern Region, Publication Number R1-89-54
