Douglas fir cone midge: what is its effect on cone development?

• A. Creates a gall on the cone scale; fuses to the ovule and causes collapse; turns into grub apartment; no external evidence unless severe, cone dies prematurely.
• B. Bores into seeds; leaves external frass.
• C. Lays eggs on foliage and sucks seeds.
• D. Overwinters as a larva in soil.

Answer: (A)

The key idea is that the Douglas-fir cone midge disrupts cone development from inside the cone. The insect lays eggs in young cones and the larvae feed within the cone tissue, producing a gall on the cone scale. This gall can fuse with the ovule, blocking normal seed formation and causing the cone to collapse or die prematurely. Because the damage happens inside the cone, there may be little or no external sign unless the infestation is severe, in which case many cones are deformed or fail to develop seeds. This internal, seed-formation–oriented damage distinguishes it from pests that bore seeds with visible frass, feed on foliage, or overwinter in soil.