Balsam gall midge
Hosts: Balsam and Fraser firs
Evidence: Larvae initiate the formation of galls, which appear as swollen oval growths about 3 mm in diameter at the base of needles mid-June. Galled needles turn yellow and begin to drop from the twigs in October.
Life cycle: There is one generation per year. The gall midge overwinters as a larva in the soil under an infested host tree. Pupation takes place in May, and soon adult flies emerge, mate and lay eggs in developing needles (a). Newly-hatched larvae settle and feed on immature needles, initiating the almost immediate growth of gall tissue which encloses the larvae (b). In late fall, larvae leave the galls and drop to the ground for the winter.
Management: Outbreaks of balsam gall midge are likely to be episodic, lasting for only 2 or 3 years before returning to very low levels for the following several years. Significant reductions in gall midge populations have been attributed to insect parasites. Where chemical control is warranted, treatments should be made when new shoots begin to flatten.
Figure a: Ronald S. Kelley, Vermont Department of Forests, Parks and Recreation, Morrisville, VT.
Figure b: Ronald S. Kelley, Vermont Department of Forests, Parks and Recreation, Morrisville, VT.
Drooz, A.T. 1985. Insects of Eastern Forests. USDA Forest Service Miscellaneous Publication 1426. p 442;
Johnson, W.T. and Lyon, H.H. 1991. Insects That Feed on Trees and Shrubs. 2nd edition. Cornell University Press. p 116-117;
Martineau, R. 1984. Insects Harmful to Forest Trees. Agriculture Canada Government Publishing Centre, Supply and Services, Ottawa. p 97-99;
Rose, A.H. and Lindquist, O.H. Revised by Syme, P. 1994. Insects of Eastern Spruces, Fir and Hemlock. Canadian Forest Service Publication. p 93.