Evaluation of Sampling Techniques for Three Biological Control Agents of Carduus Thistles

Publisher Website
Google Scholar
Abstract
Suction, visual, and pan sampling were evaluated in relation to their efficiency for population estimates of Rhinocyllus conicus, Trichosirocalus horridus, and Cassida rubiginosa. The duration of suction did not influence their removal from musk thistle rosettes. Significantly fewer R. conicus adults were removed from thistle rosettes in a simulated grazed habitat than in an ungrazed habitat. No differences occurred in removal by suction sampling between habitats for either T. horridus or C. rubiginosa. Removal by suction sampling was not dependent on density. Suction sampling and visual searches provided for equal numbers of R. conicus for short (50 cm) thistles. More T. horridus were found by suction sampling than by visual counts for all thistle height categories. Pan sampling yielded nearly equal numbers of T. horridus and slightly fewer R. conicus and C. rubiginosa when compared with visual counts. The pan technique was less variable. Relative net precision estimates indicated that the pan technique was superior in overall efficiency to visual counts for each insect.