The Relative Efficiency and Reliability of Three Methods for Sampling Arthropods in Australian Cotton Fields

Population densities of 26 species or groups of arthropods were assessed by: (1) 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 of crop 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 categories. Fewer bag than visual samples were required for a given level of reliability of population estimate. The bag method was the most expensive and the sweep method the least expensive at any level of reliability. The sweep method could not be used to detect eggs and very small larvae of Heliothis spp. nor could it be used to sample cotton fruit. Choice between the visual and sweep methods depends on the arthropods it is wished to sample.