Biology of a Pinyon Spindle Gall Midge (Diptera: Cecidomyiidae)1

Pinyonia edulicola Gagné caused a spindle-shaped needle gall on pinyon, Piuus edulis Engelm. Infested needles were killed and dropped prematurely. P. edulicola had 1 generation per year. The adults emerged from mid-June until mid-July, mated, and immediately laid eggs on the developing needles. Eggs hatched in about 1 week and the larvae moved down between the needles to feed at the base. Feeding appeared to be associated with gall formation with the new plant tissue enveloping the larvae. Five to 40 larvae were found inside each gall and remained there until late May of the next year. At that time a frothy communal pupal case was formed inside the gall. The pupal stage lasted from late May until mid-June. The pupae then moved up between the needles, shed their pupal cases and emerged as adults. Many of the midges were parasitized by Platygaster sp., which oviposited in the midge egg.