Pest management decisions in an integrated pest management strategy rely on pest thresholds; however, thresholds have been poorly defined and investigated in greenhouse ornamental production, often resulting in prophylactic use of insecticides. For example, management of whiteflies (Aleyrodidae) on poinsettia (Euphorbia pulcherrima) historically has relied on regular applications of insecticides (Palumbo et al., 2001; Sharaf, 1986; Stevens et al., 2000), with some growers applying insecticides every 3 to 5 d (Hoddle and Van Driesche, 1996). However, relying on regular insecticide applications as a pest management strategy may be short-sighted because of the risk of insecticide resistance (Palumbo et al., 2001; Schuster et al., 2010; van Lenteren, 2012), increasingly tighter federal and state pesticide regulations (U.S. Environmental Protection Agency, 2017), and increasing pressure from retailers against the use of specific insecticide classes by commercial growers (Friends of the Earth, 2017). Augmentative biological control (i.e., the regular release of natural enemies to reduce the target pest population to acceptable levels) is a promising strategy that has been increasingly adopted in many areas of the world, including parts of Europe, Asia, and Latin America (Barratt et al., 2018). However, information related to starting pest densities at the grower and acceptable pest densities by the retailer needed for development of an augmentative biological control strategy in ornamental production in the United States is lacking.
Successful management of whiteflies in an augmentative biological control program for poinsettias requires favorable conditions: lack of insecticide residue, few or limited pest species, and low starting whitefly densities (Van Driesche et al., 1999). Suppression of whiteflies has been considered unsuccessful using parasitic wasps, such as Eretmocerus eremicus, when initial whitefly densities were greater than 1.0 whiteflies (all life stages) per poinsettia cutting (Van Driesche et al., 1999). Propagative plant materials have been suggested as a major source of whitefly populations in poinsettia production (Buitenhuis et al., 2016); however, there is limited published data to support this assertion. Dipping cuttings, or “immersion,” in a pesticide mixture has been suggested as a method to start “clean” as a prerequisite for a successful biological control program (Brownbridge et al., 2014; Buitenhuis et al., 2016; Krauter et al., 2017). More surveys of poinsettia cuttings from propagators will aid in determining whether the cost of preemptive insecticide treatments of poinsettia propagative materials is justified.
Poinsettias at retailers are not likely completely free of pests, but the acceptable density of whiteflies at retailers has not been determined. The economic threshold on ornamentals has been generally defined as “low” (Stevens et al., 2000) or “essentially zero” (Bethke and Cloyd, 2009), because any pest injury is considered unacceptable. Documented final densities for whiteflies on poinsettias has been limited to retailers in Massachusetts (Hoddle and Van Driesche, 1996; Van Driesche et al., 1999). Implementation of augmentative biological control in poinsettia production requires a better understanding of current accepted whitefly densities at the retailers. In this study, we determine the starting infestation levels of whiteflies on rooted poinsettia cuttings at grower facilities and determine whitefly densities on finished poinsettias at the retailer.
Barratt, B.I.P., Moran, V.C., Bigler, F. & van Lenteren, J.C. 2018 The status of biological control and recommendations for improving uptake for the future BioControl 63 155 167
Benjamini, Y. & Hochberg, Y. 1995 Controlling the false discovery rate: A practical and powerful approach to multiple testing J. R. Stat. Soc. B 57 289 300
Brownbridge, M., Buitenhuis, R., Saito, T., Brommit, A., Cote, P. & Murphy, G. 2014 Prevention is better than cure: Early-season intervention to control whitefly on poinsettia Integr. Control Prot. Crop. Temp. Clim. IOBC WPRS Bull. 102 23 28
Buitenhuis, R., Brownbridge, M., Brommit, A., Saito, T. & Murphy, G. 2016 How to start with a clean crop: Biopesticide dips reduce populations of Bemisia tabaci (Hemiptera: Aleyrodidae) on greenhouse poinsettia propagative cuttings Insects 7 48
Friends of the Earth 2017 Nursery and retailer commitments. 20 Oct. 2019. <https://foe.org/nursery-retailer-commitments/>
Hoddle, M.S. & Van Driesche, R.G. 1996 Evaluation of Encarsia formosa (Hymenoptera: Aphelinidae) to control Bemisia argentifolii (Homoptera: Aleyrodidae) on poinsettia (Euphorbia pulcherrima): A lifetable analysis Fla. Entomol. 79 1 12
Krauter, P.C., Heinz, K.M. & Arthurs, S. 2017 Protecting unrooted cuttings from sweetpotato whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae), during propagation J. Insect Sci. 17 4 486 491
Liu, T.-X., Oetting, R.D. & Buntin, G.D. 1993 Distribution of Trialeurodes vaporariorum and Bemisia tabaci (Homoptera: Aleyrodidae) on some greenhouse-grown ornamental plants J. Entomol. Sci. 28 102 112
Medina-Ortega, K.J. 2011 Poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch: Euphorbiacea) resistance mechanisms against the silverleaf whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) biotype B. Ohio State Univ., Columbus, PhD Diss
Schuster, D.J., Mann, R.S., Toapanta, M., Cordero, R., Thompson, S., Cyman, S. & Morris, R.F. 2010 Monitoring neonicotinoid resistance in biotype B of Bemisia tabaci in Florida Pest Mgt. Sci. 66 186 195
Stevens, T.J., Kilmer, R.L. & Glenn, S.J. 2000 An economic comparison of biological and conventional control strategies for whiteflies (Homoptera: Aleyrodidae) in greenhouse poinsettias J. Econ. Entomol. 93 623 629
U.S. Environmental Protection Agency 2017 Revised certification standards for pesticide applicators. 4 May 2017. <https://www.epa.gov/pesticide-worker-safety/revised-certification-standards-pesticide-applicators>
Van Driesche, R.G., Lyon, S.M., Hoddle, M.S., Roy, S. & Sanderson, J.P. 1999 Assessment of cost and performance of Eretmocerus eremicus (Hymenoptera: Aphelinidae) for whitefly (Homoptera: Aleyrodidae) control in commercial poinsettias crops Florida Entomol. Soc. 82 570 594
van Lenteren, J.C. 2012 The state of commercial augmentative biological control: Plenty of natural enemies, but a frustrating lack of uptake BioControl 57 1 20
Wickham, H. 2016 ggplot2: Elegant graphics for data analysis. Springer-Verlag, New York, NY