Are these cones?

Asked August 27, 2017, 7:02 PM EDT

We saw these cone-like things growing on juniper trees next to juniper berries which I thought were the cones for junipers and the pollen cones so we're wondering what these are?

Multnomah County Oregon

1 Response

Those unusual formations on the juniper are galls formed by the interaction of the tree with the activities of some very small flies (Oligotrophus betheli) in the family Cecidomyiidae.

Here’s how that occurs. The adult females lay eggs in growing juniper tissue. When the larvae (youngsters) hatch, they inject salivary fluids into the plant tissues as they feed. The tissue then grows at an accelerated rate to form a shelter around the larvae, protecting them from weather and their natural enemies. After the flies complete their development, they exit by way of very small holes they make at the base of the galls. The galls may be green or reddish before the insects exit, then become brown (as in your image).

Insect-caused galls are interesting in that each kind of insect forms a gall characteristic of its species. Although people sometimes consider such galls unsightly, they don’t affect the health of the plant. Management is limited to removing the gall(s).

See “Pest Profile – Juniper tip midge” and “Utah juniper”