Balsam gall midge

Balsam fir twig seriously damaged Thérèse Arcand

French common name: Cécidomyie du sapin
Scientific name: Paradiplosis tumifex Gagné
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Diptera
Family: Cecidomyiidae

Distribution

Canada

Damage, symptoms and biology

Balsam gall midge damage appears on current-year needles as early as late June and persists until fall. The larvae initiate the formation of galls, which appear as swollen growths at the base of the needles; several galls can be seen on a single needle. Each gall contains a larva, which feeds on the internal tissue of the needle. Galled needles turn yellow and dry out, causing them to drop prematurely in the fall.

Repeated severe infestations can cause tree growth loss but does not result in mortality.

The appearance of the adults in May coincides with the development of fir buds. The female lays her eggs between the tight needles of the opening buds. Each newly hatched larva crawls to the base of a needle, where it settles and begins to feed, initiating the growth of gall tissue, which ultimately completely encloses the larva, thus forming the gall.

The larva leaves the gall in the fall and drops to the ground where it overwinters.

Other information

A species native to North America, the balsam gall midge occurs throughout the range of fir. In Canada, it is particularly damaging to Christmas tree plantations and in Quebec, it is monitored by the Réseau d’avertissements phytosanitaires (RAP), the province’s plant pest warning system.

The balsam gall midge was first recorded in eastern Canada in 1938 and since then, it has been regularly reported. Infestations are generally of short duration, i.e. roughly three years.

In urban environments, treatment is generally unnecessary, because after the galled needles drop in the fall, there is no visible damage the following spring. During severe outbreaks, control measures against this insect are justified only to protect the foliage of firs to be sold as Christmas trees.