|Elliott, Norman - Norm|
Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/31/2006
Publication Date: 4/25/2006
Citation: Elliott, N.C., Tao, F.L., Fuentes-Granados, R., Giles, K.L., Elliott, D.T., Greenstone, M.H., Shufran, K.A., Royer, T.A. 2006. D-vac sampling for predatory arthropods in winter wheat. Biological Control. 38:325-330. Interpretive Summary: Predatory insects and other predatory arthropods are common in winter wheat fields in the United States. The role played by these predatory arthropods in biological control of cereal aphids in winter wheat has yet to be determined. It is exceedingly difficult and time consuming to obtain reliable estimates of populations of insects and other arthropods in crops. Several machines have been devised to simplify the process of estimating arthropod populations. The D-vac is a well-known machine for sampling arthropods based on the vacuum principle, much like a vacuum cleaner used in the home. However, the efficiency of the D-vac for collecting arthropods varies with the species of arthropod and with environmental conditions, so that samples taken with it may or may not yield reliable estimates of population density. We conducted a study to determine the utility of the D-vac for sampling predatory arthropods in winter wheat fields. We found that the sampling efficiency was variable for predators in wheat fields and depended on several environmental factors. The D-vac was a poor tool for sampling adult lady beetles (Coccinellidae) and adult ground beetles (Carabidae). But for larval Coccinellidae, lacewing (Chrysopidae) adults and nymphs, spiders, and rove beetles (Staphylinidae) the D-vac sampling was useful for estimating population density in winter wheat fields provided estimates were adjusted for environmental conditions (for example temperature and crop growth stage) at the time of sampling. The results of the study establish guidelines for how to use the D-vac to estimate populations of arthropods in winter wheat fields to determine their importance in the biological control of cereal aphids.
Technical Abstract: We evaluated the D-vac for sampling predatory arthropods in winter wheat fields in Oklahoma. Mean sampling efficiency of D-vac sampling was low for adult Coccinellidae and Carabidae. Capture efficiency was greater for coccinellid larvae than for adults. Capture efficiency was high for adult and immature Nabidae and Chrysopidae, for spiders, and for adult Staphylinidae. For most predators there was a significant correlation between the number of individuals captured in D-vac samples and the number of individuals per m2 in the field. However, the highest correlation was 0.82 for adult Staphylinidae, and correlations for most predators were < 0.60. Significant correlations between D-vac sample estimates and ancillary abiotic and biotic variables occurred for most predators indicating that the efficiency of D-vac sampling was affected by the environment. Among the variable measures, wheat plant growth stage and air temperature were most consistently correlated with D-vac estimates. Multiple regression models were constructed to relate population estimates from D-vac sampling to absolute density, by adjusting estimates for variation in abiotic and biotic environmental variables. Among abiotic variables, air temperature and wind velocity most frequently entered into step-wise regression models for predators. Among biotic variables, wheat plant growth stage and wheat tiller density, both of which are related to habitat structure, entered most frequently into models. Regression models had coefficients of determination ranging from 0.10 for adult Carabidae to 0.70 for Chrysopidae nymphs. Low coefficients of determination for adult Coccinellidae and adult Carabidae indicated that the D-vac was a poor tool for sampling those predators in wheat fields. Higher coefficients of determination for larval Coccinellidae, Chrysopidae adults and nymphs, spiders, and Staphylinidae indicated that D-vac sampling was useful for sampling those predators to obtain estimates of population density in winter wheat fields.