THE RELATIVE EFFICIENCY AND RELIABILITI ’ OF THREE METHODS FOR SAMPLING ARTHROPODS IR: AUSTRALIAN COTTON FIELDS

Population densities of 26 species or groups of arthropods were assessed by: (I visual field inspection of single cotton plants: (2) laboratory inspection of single plants placed in plastic bags in the field: and (3) laboratory inspection of sweep-net catches from 30 m ofcrop row. Sampling was carried out in a total of 6 fields in 3 years. The sweep method gave the lowest estimates of population densities for almost all cate orieb Fewer bag than visual samples were required fora given level ofreliability ofpopulation estimate. The%ag method was the most expensive and the sweep method the least expensive at any level ofreliability. Thesweepmethodcould not beused todetect eggsand verysmall larvaeofH~~liorhi.sspp. norcould i t beused to sample cotton fruit. Choice between the visual and sweep methods depends on the arthropods it is wished to sample