The influence of Aceria chondrillae on the growth and reproductive capacity of Chondrilla juncea.
The effects of 2 levels of infestation by Phytoptus chondrillae G. Can. (Aceria chondrillae) on inflorescence growth and reproductive capacity of Chondrilla juncea were examined in a glasshouse experiment. Significant effects were observed on the gross morphology of the plant, measured as a decrease in primary and secondary stem growth, in the production of basal axillary stems and as an altered stem-leaf morphology. The presence of mites significantly changed the fate of growing points, increasing their mortality and producing large numbers of galls. The number of flowers was severely reduced and root weight and capacity to regenerate rosettes significantly decreased. The results are related to field observations made since the specific introduction of P. chondrillae to Australia in 1971 for the control of C. juncea, and to the usefulness of gall formers generally as agents for the biological control of weeds.