Cone and Seed Insects

Pine Seed Chalcid
Megastigmus albifrons (Walker)

Host:  Ponderosa pine

Figure 156. Figure 156. Larva and seed damage caused by the pine seed chalcid.

Symptoms/Signs:  Adults are antlike in appearance and range in color from yellow to black or brown. Females have a long, curved ovipositor. The larvae are small, white and legless. The outer seedcoat develops normally and shows no evidence of an oviposited egg. When adults emerge they leave a small round hole in the seedcoat.

Biology:  Adult emergence lasts for about a month in spring. Females may mate or reproduce parthenogenetically. Eggs are oviposited through the young scales of developing cones directly into the seed. Usually one egg is laid per seed. The larva matures in the seed, consuming its entire contents. The insect overwinters in the seed and pupates in early spring. Some adults emerge at this time while others may diapause for up to 3 years.

Effects:  Pine seed chalcid can cause a large percentage of cull seed in commercial seed production operations. Since it is very difficult to distinguish between healthy and inhabited seed, insects are unknowingly transported.

Similar Insects and Diseases:  There are a variety of cone and seed feeding insects in the West. Larvae of the family Cecidomyiidae (Diptera) may cause similar reductions in seed production; however, the larvae are not voracious feeders and damage to cones and conelets results from gall formation on the seed scale which prevents seed dispersal. Other species of insects that feed in seeds and cones of ponderosa pine in the Southwest include ponderosa pine cone beetle (Conophthorus ponderosae), pine coneworm (Dioryctria auranticella), and the ponderosa pine seed moth (Laspeyresia piperana).

References:  3, 15