Use of multiple natural enemies for inoculative biological control of Bemisia tabaci in greenhouse poinsettia production

Abstract

Two natural enemies, Eretmocerus eremicus Rose & Zolnerowich (Hymenoptera: Aphelinidae) and Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae), that differ in their feeding niches were selected to determine whether the combination of natural enemies provides superior suppression of sweetpotato whiteflies, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), on poinsettias [Euphorbia pulcherrima Willd. ex Klotz. (Malpighiales: Euphorbiaceae)] compared to either natural enemy species alone. I started by surveying initial B. tabaci densities on poinsettia cuttings received by growers and retailer thresholds of finished poinsettias over two years. Initial B. tabaci densities were 0.1 nymphs per cutting received by growers and up to an average of 73 B. tabaci nymphs per finished poinsettia at any given retailer.

In caged greenhouse experiments, I investigated B. tabaci suppression by the combination of E. eremicus and A. swirskii compared to each natural enemy alone. Ultimately, the combination treatment suppressed B. tabaci population growth similarly to either natural enemy alone. In a separate set of caged greenhouse experiments, I challenged natural enemy (single species or combination) suppression of B. tabaci by modifying the natural enemy release schedule (one-week delay at weeks 4 and 8) and simulating B. tabaci immigration (at weeks 4 or 8). The combination of E. eremicus and A. swirskii maintained superior suppression of B. tabaci compared to E. eremicus alone. All combination natural enemy treatments ultimately resulted in B. tabaci densities that were below retailer thresholds on finished poinsettias.

Lastly, I compared the use of a seasonal inoculative biological control program using E. eremicus and A. swirskii to manage B. tabaci compared to conventional insecticide use in commercial poinsettia production at three grower facilities in east Texas. At all grower locations, B. tabaci densities were consistently similar or higher than the conventionally managed greenhouse; however, final B. tabaci densities were below retailer acceptable densities in all treatments. The cost of inputs for the biological control program was lower ($0.057) or higher ($0.178) than frequently reported insecticide input costs for 15.2-cm potted poinsettias ($0.09). My dissertation demonstrates effective and potentially economic use of multiple natural enemies for B. tabaci suppression in commercial poinsettia production for the first time.