Host range and potential distribution of Aceria thalgi (Acari: Eriophyidae): a biological control agent for Sonchus species

Sowthistles, S onchus arvensis , S . asper and S . oleraceus ( A steraceae), are serious weeds that impact on crop production in many regions of the world. A recently described eriophyid mite, A ceria thalgi from S onchus species found in southern A ustralia, was assessed for its potential as a biological control agent for these weeds. Glasshouse host range testing and field observations of 11 species from seven genera from the L actuceae tribe of A steraceae showed that A . thalgi survived only on plants within the S onchinae subtribe ( S . asper , S . oleraceus and S . hydrophilus ) and not on the closely related A ctites megalocarpus , R eichardia tingitana or other test plants. Under glasshouse conditions and varying plant ages, A . thalgi infestation caused significant growth reduction of the exotic species S . oleraceus (up to 97%) and, to a lesser extent, the A ustralian native S . hydrophilus (up to 33%). Six temperatures from 9.1 to 33.7°C were used to determine population growth parameters for A . thalgi . The range of temperatures suitable for population growth was used to modify a CLIMEX model based on its host S . oleraceus . The projected world distribution of the CLIMEX model indicates that the mite could establish in some areas of N orth A merica, making it a possibility for an augmentative approach to biological control of S onchus spp. in that region. The model confirms the potential for a widespread distribution of A . thalgi in southern A ustralia where it could be considered for a conservative approach to biological control of S onchus spp. in cropping systems.