Abiotic and biotic variables affect aphid natural enemy population estimates on sorghum

Authors: Elliott, Norman; HAYASHIDA, RAFAEL - Oklahoma State University; GILES, KRISTOPHER - Oklahoma State University; VAZQUEZ, NINA - Oklahoma State University; MUYOMBO-DIBUE, EPHRAIM - University Of Florida; HOBACK, WYATT - Oklahoma State University

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2026
Publication Date: 4/27/2026
Citation: Elliott, N.C., Hayashida, R., Giles, K.L., Vazquez, N., Muyombo-Dibue, E., Hoback, W. 2026. Abiotic and biotic variables affect aphid natural enemy population estimates on sorghum. Biological Control. 119(3):2365-2372. https://doi.org/10.1093/jee/toag115.
DOI: https://doi.org/10.1093/jee/toag115

Interpretive Summary: Arthropods that prey on aphids in grain sorghum fields in the U.S. Great Plains provide naturally occurring biological control of aphids and are thought to be important for greenbug and sorghum aphid control. However, more detailed research is required to determine their importance. We evaluated four methods for sampling in sorghum for their reliability for estimating population densities of the natural enemies. Mathematical regression models for natural population density (D) versus relative density (R) obtained using the sampling methods fit the data well for many species of natural enemy, but not all of them. The results are encouraging because they indicate that useful estimates of population for the natural enemies can be obtained using relative sampling methods. The significance of the research lies in the fact that measurements of population density are essential for studies of to determine the importance and relative importance of each type of natural enemy for controlling aphid pests in sorghum.

Technical Abstract: Aphidophagous arthropods inhabit grain sorghum, Sorghum bicolor (L.), fields in the U.S. Great Plains. They provide naturally occurring biological control of aphids in sorghum, and are important for greenbug, Schizaphis graminum (Rondoni) and sorghum aphid, Melanaphis sorghi (Theobald), control. We evaluated four methods for sampling aphidophagous arthropods in sorghum for their reliability for estimating population densities: suction sampling, sweepnet sampling, counting natural enemies for a fixed time, and counting natural enemies on two sorghum leaves per plant. We compared population estimates obtained by these methods to estimates of absolute population achieved by complete enumeration of natural enemies on sorghum plants. Using partial correlation analyses we found that sorghum plant growth stage, aphid population intensity, and some meteorological variables were related to relative population and population intensity estimates for some natural enemies. Aphid population intensity and sorghum plant growth stage were the ancillary variables most frequently correlated to natural enemy relative density or population intensity. Significant partial correlations tended to be specific to particular natural enemy categories and sampling methods. Regression models were constructed to relate absolute population density (D) of natural enemies to relative population density or population intensity (R). Regression models for coccinellid adults and large larvae had relatively large R2 ranging from 0.66 to 0.80 for all sampling methods. Regression models for A. nigritus from 2-leaf counts and timed counts had small R2 of 0.16 and 0.33. Regression models for lacewing larvae were not significant. Relative density (R) was the only variable that entered significantly into regression models for absolute population density (D) for most natural enemy categories. Ancillary variables entered more frequently in D versus R models for converting 2-leaf counts than for any other sampling method. The results are encouraging because they indicate that useful estimates of absolute population can be obtained using relative sampling methods.