Fourth International Bemisia Workshop International Whitefly Genomics Workshop
Monitoring of Imidacloprid Resistance in Biotype B of Bemisia tabaci in Florida
1 University of Florida, IFAS, Gulf Coast Research and Education Center, Wimauma, FL, USA. Correspondence: mannrs@ufl.edu
2 B & W Quality Growers, Inc., Fellsmere, FL, USA
3 Bayer CropScience, Lakeland, FL, USA
Biotype B of the sweetpotato whitefly, Bemisia tabaci (Genn.), is a worldwide pest that has developed resistance to many insecticides, including the novel neonicotinoid class. Field populations were collected from 2000 to 2006 from different locations in Florida and were compared for their susceptibility to the neonicotinoid imidacloprid (Bayer Crop Science) using a cut leaf petiole bioassay method. Three whitefly populations collected in 2000 showed high susceptibility to imidacloprid, with a maximum resistance ratio (RS50) of 6.00. Whitefly susceptibility was lower in 2001, 2002 and 2003 with 3 out of 12 bioassayed populations indicating RS50 values over 10.0 during 2001, 4 out of 15 during 2002 and 14 out of 21 during 2003. The maximum resistance ratio also showed a similar pattern with RS50 values of 14.6, 35.2 and 28.1 for 2001, 2002 and 2003, respectively. The populations showed increased susceptibility during 2004 and 2005 with only 2 populations out of 17 recording RS50 values over 10.0 during 2004 and none out of 2 during 2005. The maximum RS50 value also decreased to 11.4 during 2004 and 2.59 during 2005. Whitefly populations collected during 2006 again showed reduced susceptibility, with 6 out of 8 populations recording RS50 values above 10.0 and with the maximum RS50 value being 45.51. Rearing whitefly populations in the laboratory for 4–6 generations without exposure to imidacloprid resulted in RS50 values declining by 75 to 80 per cent to acceptable levels during 2001 and 2002. Similar decreases are also being observed with 2006 populations. All of the 2006 populations were tested and confirmed to be biotype B. Therefore, biotype B possesses the potential to develop unstable tolerance to imidacloprid, and monitoring for imidacloprid resistance needs to continue in Florida.