Biology and host specificity of the Chondrilla gall mite Aceria chondrillae (G. Can.) (Acarina, Eriophyidae)

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Abstract
The Eriophyid gall mite, Aceria chondrillae (G. Can.), which is distributed from south-east Russia to Portugal, was studied in the Mediterranean region as part of a biological control programme against skeleton weed (Chondrilla juncea) for Australia. The mite induces the vegetative and flower buds of Chondrilla to form leafy galls in which the full life-cycle is completed, causing stunting of the plant and reducing seeding. The mite overwinters in the rosettes of C. juncea without inducing gall development or reproducing. Populations decrease markedly during winter, recover in spring and infestations spread rapidly during summer. Reproduction is sexual and spermatophores are deposited by the males. Amblyseius sp. preys on A. chondrillae without marked effect. Tests made by placing fully developed galls of A. chondrillae on 75 species of plant including certain Cichoriaceae closely related to Chondrilla showed that the mite was highly specific to Chondrilla. Comparative tests with four geographical strains of A. chondrillae against six forms of C. juncea of various geographical origins indicated that the strains were specialised to their usual host form of the plant. A Greek strain of the mite readily attacked the main Australian form of C. juncea, and this strain has been introduced into Australia as a biological control agent for the weed.