Dose‐response testing of Australian populations of onion thrips
Field strains of Thrips tabaci Lindeman were collected from bulb onion in New South Wales, Queensland and South Australia and returned to the laboratory for culturing and subsequent bioassay to determine chemical specific responses. Chemicals tested included diazinon, dimethoate, λ‐cyhalothrin and methidathion with imidacloprid and spinetoram evaluated to establish reliable susceptible baseline responses. Reference (susceptible) responses were compared back with those previously published and for all insecticides more susceptible strains were found for resistance comparison. Results for methidathion in particular were found to be significantly different from those reported previously. These differences influenced resistance factor calculation considerably. A high 49‐fold methidathion resistance was detected, a result consistent with anecdotal grower concerns of poor product performance against T. tabaci. Resistance to diazinon remains generally low with all strains tested showing <6‐fold at the LC50 level. LC50 dimethoate resistance peaked at 17‐fold. Maximum (56‐fold) λ‐cyhalothrin resistance was significantly less than previously found but responses were very heterogeneous implying resistance could very quickly increase. Worryingly, the difference in imidacloprid responses between the least and most tolerant was 41‐fold although the chemical is neither used nor registered for use against T. tabaci. We consider such a high and significant difference in response to imidacloprid is most likely caused by an unknown cross‐resistance that may compromise any future development of imidacloprid for use against T. tabaci. Thrips remain susceptible to spinetoram.
Document Type: Research Article
Affiliations: 1: Industry and Investment NSW, Elizabeth Macarthur Agricultural Institute, Private Bag 4008, Narellan, NSW 2567, Australia 2: Industry and Investment NSW, Yanco Agricultural Institute, Private Mail Bag, Yanco, NSW 2703, Australia
Publication date: November 1, 2011