Sampling Insects

Arthropod sampling in field crops and ground covers has been optimized at NMSU by building and using mechanical, pusher and self-propelled, 4,200 CFM high-vacuum machines (Insectavacs) which have been calibrated (relative/absolute) for 24 genera of beneficial and phytophagous arthropods. Taking samples with these machines is faster, more accurate, and more cost effective than conventional sampling methods but requires more hand counting for evaluation. The objective is to sample the primary consumers, parasitoids and predators in agricultural systems to predict mortality of phytophagous species. Cotton ecosystems are difficult to sample because there are so many species present and they generally occur in high numbers in clumped distributions (Ellington et al. 1996). Obtaining statistically relevant density estimations of primary consumers, predators and parasitoids requires large replicated samples (Ellington et al. 1996).

. Acquiring samples - A small four wheel drive (hydraulically driven) self propelled platform [Insectavac (IV)] with a 4,200 cfm high vacuum fan has been designed and built to take representative cotton insect samples (Ellington et al. 1984b).

. Calibration - The IV collector was calibrated for 24 genera of insects by comparing 83, 100 ft relative vacuum samples in three cotton fields to 830, 2.4 ft absolute samples in the same fields. Accuracy of density estimates depends on density and degree of clumping of insect populations and sampling protocol. Most primary consumers, predators and parasitoids can be collected very efficiently using the IV; however, bollworm eggs and larvae must be counted in traditional ways. IV densities can be converted to absolute or sweep net densities if needed (Ellington et al. 1984c).

. Sample size - The optimum size and number of samples needed to estimate the mean density of 24 genera of insects was determined by vacuum sampling 590, 100 ft quadrats end to end 12 times over a three year period in three cotton fields. Data for each date and location were pooled and the data analyzed as a nested design. It was found that it took four 100 ft vacuum samples per cotton field to estimate the mean density of most insect species to within 80 ± 5% of their true value (Ellington and Southward 1996). Density estimates for genera collected by sweep net were only within 7 ± 5% of their true value.