Plant Growth Hormones in Pinyon Insect Galls

BYERS J. A., BREWER J. W. & DENNA D. W. 1976. Plant growth hormones in pinyon insect galls. Marcellio 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 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. Rbumd-Les larves de la Ckidomyide Janetiella sp. (esp6ce voisine de J. colomdensis Felt) provoquent des galles i la base des jeunes aiguilles de Pinus edulis Engelm. Les tests biologiques effectuds avec des extraits de ces galles montrent qu'elles prdsentent une activiti auxinique plus de 17 fois supirieure i celle des extraits de feuilles normales du meme 8ge et une activitd de type gibbdrellique 'plus de 21 fois supirieure aux extraits des feuilles tdmoins. Les concentrations les plus ilevies de ces substances de croissance (par unitd de volume) sont ddceldes pendant les premiers stades cdcidogsnes, bien que des quantitis anormalement dlevdes aient dtd trouvdes pendant la gr iode de croissance rapide de la galle. Les extraits larvaires ne contiennent pas de quantitds ddtectables d'auxine, mais des traces de substances ayant une activiti du type gibbdrelline. L'hypertrophie cellulaire et lhyperplasie qui interviennent dans le ddveloppement dcidogsne sont des manifestations favorables h l'idde que des substances controllant la croissance telles que des auxines ou des gibbdrellines jouent probablement un rBle important dam la formation de cette galle.