Byers, J.A., Brewer, J.W., & Denna, D.W. 1976. Plant growth hormones in pinyon insect galls. Marcellia 39:125-134.

Abstract-- Larvae of the midge Janetiella sp. near J. coloradensis Felt (Diptera: Cecidomyiidae) cause galls at the base of young needles of pinyon Pinus edulis Engelm. Bioassays of extracts from these galls contained as much as 17 times more auxin activity and as much as 21 times
normal needle galled needle
Normal needle (left) and round gall cross section at same magnification and general area.
more gibberellin-like activity per needle than extracts from normal needles of the same age. The highest levels of these plant growth substances (per unit volume) occurred during the early stages of gall formation, although abnormally high quantities were found throughout the period of rapid gall growth. Extracts round galls and normal needle of insect larvae did not contain auxins at detectable levels but traces of substances with gibberellin-like activity were present. Cellular hypertrophy and hyperplasia also support the idea that plant growth controlling substances such as auxins and/or gibberellins probably play an important role in gall formation.

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Chemical Ecology