Monterey pine midge—Thecodiplosis piniradiatae
Monterey pine midge (family Cecidomyiidae) larvae feed in and on galls, needles, and shoot terminals of pines. In California it is most common in the Central Coast and San Francisco Bay Area.
Adult Monterey pine midges, mature larvae (third instars), and pupae are all about 1/8 inch (3 mm) long. The adult is a grayish, mosquitolike fly with long thin antennae and legs. Eggs are cylindrical, pale, and about 1/50 inch (0.5 mm) long. They occur on the base of pine needle buds. Larvae are distinctly segmented and orange to white. They feed within needles. The pupa is oblong and as it ages it develops dark eyes and adult appendages.
Monterey pine midge develops through four life stages: egg, larva, pupa, and adult. Adults emerge from January to March. After mating, females lay eggs between the scales of terminal buds. The hatching larvae feed inside needles through the summer as they develop through three increasingly larger instars. Larvae mature in the fall and prepupae overwinter in needles or they drop and remain in organic litter or topsoil beneath infested pines. Pupation happens in winter and adults then emerge. Monterey pine midge has one generation per year.
Larvae of Monterey pine midge chew and feed inside the base of the newly formed needles of Monterey pine and other pines. This causes needles to swell at their base and shoot terminals to become distorted. Infested needles and shoots remain abnormally short. Heavily infested twigs are sometimes killed, harming the aesthetic value of infested trees. However, Monterey pine midge does not threaten the health and survival of otherwise healthy pines.
Provide pines a good growing environment and proper plant care so they are more tolerant of pest damage. Control is generally not warranted for Monterey pine midge. No management is known.
Adapted from 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).
A shoot with needles swollen at the base from feeding of Monterey pine midge larvae.
A shoot browned, distorted, and swollen from feeding of Monterey pine midge larvae.
Last instar (larva, left) and adult of Monterey pine midge.