Douglas-fir needle midges—Contarinia spp.
Larvae of at least three species of gall midges (family Cecidomyiidae) feed in and gall needles of Douglas-fir in California. Contarinia pseudotsugae is the most common species and C. constricta and C. cuniculator are also present.
The adults are tiny and present for only a few weeks in the spring. Larvae occur hidden inside needles. Therefore, damage from their feeding (as described below) generally first indicates the presence of these pests.
Adults are delicate, mosquitolike flies. The antennae and legs are long and thin, and the body is orange to yellowish brown. Eggs are oblong, translucent orange to yellow, and about 1/50 inch (0.5 mm) long. Adults, last instars (larvae), and pupae are about 1/12 inch (2 mm) long. The larvae are distinctly segmented and whitish to yellow. The oblong pupae occur in a silken cocoon in organic debris on the ground or in topsoil.
Douglas-fir needle midge develops through 4 life stages: egg, larva, pupa, and adult. Adults emerge in about May, mate, and the females lay eggs on needle buds, under bud scales, and on young needles. Each female can lay about 125 eggs during her lifetime. The hatching larvae chew into the needle then chew and feed inside. There are commonly several larvae feeding in each infested needle either in separate chambers or a merged hollow within the needle.
Larvae feed for about 6 months as they develop through 3 increasingly larger instars. In late fall the mature larvae (prepupae) drop to the ground where they overwinter in a silken cocoon. Pupation and adult emergence occur in spring. Douglas-fir needle midges have 1 generation per year.
Symptoms of larvae chewing and feeding inside Douglas-fir needles first appear as a patch of yellow discoloration, which may have a dark purplish spot visible on both surfaces of the needle. As the larvae continue to feed, the needle becomes slightly swollen, sometimes bent, and changes in coloration to distinctly yellow, then black or brown. Infested needles by fall become entirely brown and may drop prematurely. When the midges are abundant, infested shoot terminals may die back.
Needle and twig midges apparently do not harm trees. Prune out damaged shoots if they are intolerable. Spraying for these midges is generally not warranted in landscapes and is of unknown effectiveness.
Adapted from Bionomics of Three Closely Related Species of Contarinia Rond. (Diptera: Cecidomyiidae) from Douglas-fir Needles, Forest Entomology Laboratory, British Columbia; Western Forest Insects (PDF), U.S. Department of Agriculture Forest Service; and Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, University of California Statewide Integrated Pest Management Program (UC IPM).
Needles discolored and bent from feeding inside by larvae of a Douglas-fir needle midge.
Needles browned from feeding inside by larvae a Douglas-fir needle midge.
Larva of Douglas-fir needle midge exposed in a needle yellowed by its feeding.
Adult Douglas-fir needle midge.