Whiteflies can develop resistance to insecticides used for their control in the greenhouse. The following is more information.
Unquestionably, chemical controls such as Marathon, Safari, Distance and Avid are presently some of the premiere whitefly management materials with poinsettias. Typically they have shown to be outstanding insecticides and have enabled growers to reduce the number of treatments previously required when managing a poinsettia crop. Unfortunately, these control materials have become regional wide management approaches with their use commonly applied during all phases of the crop’s development stages.
It needs to be remembered that insecticide resistance is a reality in our industry. For example, during the past few years Marathon has experienced widespread resistance problems against silverleaf whiteflies (Q-Biotype strain). When the same insecticide is used extensively over an extended period of time, then resistance will inevitably begin to occur. There are at least 3-dozen insecticides which whiteflies in the Bemisia genus (silverleaf whitefly) are resistant to. Consequently, it is important to try to break the cycle of continual applications of insecticides that presently work best. For example, for the past 2-3 years Safari has become the material of choice for many poinsettia growers. Simply loading up on the latest and greatest insecticide presently available will produce problems. Hoping the pest control industry will continue to be able to produce new materials after others become resistant is an approach that will eventually lead to failures.
Information from "Some Thoughts on the Biointensive IPM Approach for the Management of Whitefly on Poinsettias" by Steven K. Rettke, Ornamental IPM Program Associate, Rutgers University in the October 15, 2009 edition of the Plant & Pest Advisory, Landscape, Nursery & Turf Edition, A Rutgers Cooperative Extension Publication. http://njaes.rutgers.edu/pubs/plantandpestadvisory/2009/ln101509.pdf