Fourth International Bemisia Workshop International Whitefly Genomics Workshop
Monitoring the U. S ornamental industries B’s and Q’s
1 Subtropical Insect Research Unit, U. S. Horticultural Research Laboratory, USDA-ARS, Fort Pierce, FL, USA. Correspondence: cmckenzie@ushrl.ars.usda.gov
2 Department of Entomology, University of California, Riverside, CA, USA
3 Valent USA Corporation, Snellville, GA, USA
4 Cornell University Cooperative Extension of Suffolk County, Long Island Horticultural Research and Extension Center, Riverhead, New York, USA
5 Texas Cooperative Extension, Texas A&M University, Overton, TX, USA
6 College of Agriculture and Environmental Sciences, University of Georgia, Griffin, GA, USA
7 Mid-Florida Research and Extension Center, IFAS, University of Florida, Apopka, FL, USA
8 Society of American Florists, Alexandria, VA, USA
Biotype “Q” of Bemisia tabaci was first detected in the United States on poinsettias from a southwest retail outlet in Arizona during December 2004. During the past 20 months, biotype Q has been detected in 22 states and appears to be spreading. Although indistinguishable in appearance from silverleaf whitefly (biotype B), these insects are much less susceptible to insect growth regulators and many neonicotinoid insecticides. Our primary objective was to monitor populations of B. tabaci from grower sites throughout the United States, in an effort to document the distribution of the Q-type within the ornamental industry. The ornamental grower response to the Q biotype issue has been tremendous, and many have sent in samples for testing. Without their contribution, the extent of the Q problem in the United States would not be known. Molecular techniques used to distinguish whitefly biotypes included esterase assays, analysis of mitochondrial COI DNA sequence, and microsatellite technology. Q biotype Bemisia can be distinguished from B biotype insects based on electrophoresis of the banding patterns of their esterases and this method was used to routinely confirm biotype status results utilizing cytochrome oxidase I (COI) sequence and microsatellite data analysis. For COI and microsatellite biotype determination, DNA was extracted from single whitefly using the Cartagen Genomic DNA extraction kits following the manufacturer’s protocols (Cartagen Molecular Systems, Inc. Seattle, WA). Mitochondrial COI sequence analysis was performed, by first PCR amplification of an approximately 800 bp COI DNA fragment and then sequencing the PCR amplified DNA. Sequencing reactions were analyzed on an Applied Biosystems 3730XL sequence analyzer and the resulting sequence was compared and edited using Sequencher software (Gene Codes, Ann Arbor, MI). Biotype determination was inferred from neighbor joining methods of phylogenetic analysis of the COI sequences using CLUSTALW alignments of each sequence type. Two microsatellite primers developed by De Barro et al. (2005), BEM6 -(CA)8IMP and BEM23 -(GAA)31IMP, were found to be diagnostic for B and Q biotypes and were used to determine biotype status in conjunction with analysis of mitochondrial COI DNA sequence. Results of the monitoring effort revealed 100 % concurrence in biotype determination using COI sequence and microsatellite markers. More than one positive Q sample was reported from some states and currently 22 states have reported biotype Q. Interestingly, in over 1,000 B-biotype individuals collected from throughout the continental U.S., there was no variation in the COI sequence. However, in the Q biotype COI data from approximately 750 individuals, there were 12 polymorphic sites that created 4 different COI haplotypes. The host plant from which growers were sampling whiteflies were varied, but were predominantly poinsettias. Other host plants included gerbera daisies, hibiscus and verbena. States that were identified as positive were not overrun with biotype Q and all populations were managed. With knowledge of the whereabouts of this biotype, more effective action can be taken to manage its spread, thereby preventing considerable economic losses to the ornamental industry.