October 2005
Whitefly Q Biotype
The whitefly Q biotype has been found in Arizona and California in March of 2005, and more recently in northern Georgia. This whitefly has already become established as the dominant biotype in Europe, and its resistance to insecticides is well documented. This biotype is resistant or tolerant of nicotinoids such as imidacloprid, acetamidprid, and thiamethoxam, as well as growth regulators like pyriproxyfen and buprofezin. Endosulfan sensitivity is uncertain, but new materials such as spiromesifen and dinotefuran are reportedly effective. Unlike the current B biotype of whitefly present in Florida, the resistance in the Q biotype is stable, and does not diminish over time.
This fact should alert growers to follow resistance management recommendations, including rotation of chemicals, proper use of nicotinoids (once per season), and especially the inclusion of a two to three month crop-free period in the production cycle. Since the B biotype outcompetes the Q biotype in the absence of the aforementioned insecticides, a crop free period allows the Q biotype to move into non-crop, non-sprayed host plants where it will be displaced by the B biotype. Perimeter spraying is not recommended. Growers are also urged to refrain from using nicotinoid products on crops where they aren’t necessary to further decrease exposure to this class.
Good scouting will also be a key to control. Since the Q biotype is physically indistinguishable from the B biotype, unusual whitefly activity (higher than normal counts, reduction in control) should be reported immediately. Samples of suspect whiteflies can be sent to Cindy McKenzie at the USDA laboratory in Ft. Pierce. The guidelines are that only one whitefly should be collected per plant or plant part, 50 (10 minimum) should be collected, adults are desired (but 3rd or 4th instar nymphs or pupae accepted), and preserve them in >95% ethyl alcohol. Additional data such as collector, sample, and site specific information are also requested. Cindy can be contacted at (772) 462-5917 or cmckenzie@ushrl.ars.usda.gov (South Florida Vegetable Pest & Disease Hotline, 9/23/05).
