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