Aaron Shurtleff

Monitoring neonicotinoid resistance in biotype B of Bemisia tabaci in Florida

BACKGROUND Biotype B of the sweetpotato whitefly, Bemisia tabaci (Genn.), is a worldwide pest that has developed resistance to many insecticides, including the neonicotinoid class. Florida field populations were monitored for susceptibility to the neonicotinoids imidacloprid and thiamethoxam using a cut leaf petiole bioassay method. RESULTS Average RR(50) values for imidacloprid increased from 3.7 in 2000 to 12.0 in 2003; decreased to 5.0 and 2.5 in 2004 and 2005, respectively; and then increased to 26.3 and 23.9 in 2006 and 2007, respectively. Populations with RR(50) values of about 50 to 60 during generation one reverted to RR(50) values of < or =4 in six generations, when reared without further exposure to imidacloprid. Average RR(50) values for thiamethoxam increased from 2.0 in 2003 to 24.7 in 2006 and decreased to 10.4 in 2007. Populations with RR(50) values of about 22, 32 and 53 during generation one declined to 8, 5 and 6, respectively, after being reared for five generations without exposure to thiamethoxam. The correlation coefficient from the 26 populations that were bioassayed both with imidacloprid and thiamethoxam showed a significant positive correlation (R(2) = 0.58) between these populations. CONCLUSION The high level of RR(50) values to imidacloprid and thiamethoxam suggest an unstable decline in the susceptibility of B. tabaci to imidacloprid and thiamethoxam, with possible cross-resistance or predisposition for dual resistance selection.

MANAGEMENT OF THE SILVERLEAF WHITEFLY ON FRESH MARKET TOMATOES WITH SOIL AND FOLIAR INSECTICIDE APPLICATIONS, SPRING 2002

On 28 Feb, transplants were set 18 inches apart on raised beds of EauGallie fine sand soil covered with white on black low density polyethylene mulch. Plots were three, 21-ft-long rows on 10-ft aisles and 5-ft centers and were irrigated by a seepage sub-irrigation system. Treatments were replicated four times in a RCB design. Admire, Platinum and V-10112 were applied on 28 Feb to each plant in 4 oz of water. Activol, Aza-Direct and Hexacide were applied weekly. The remaining products were to have been applied at the pre-determined density of five whitefly sessile nymphs and/or pupae/10 leaflets (Table 1); however, on 9 May only treatments with Oberon were applied before uncontrollable circumstances stopped spraying. All treatments were applied on 26 May. Foliar applications were made with a high clearance, self-propelled sprayer operated at 200 psi and 3.4 mph. It was fitted with eight Albuz orange nozzles per row and delivered 90 (six nozzles open) or 120 (eight nozzles open) gpa. Because of a heavy population of southern armyworm larvae, Javelin (2 lb/acre), XenTari (2 lb/acre), Confirm 2F(16 oz/acre) or Avaunt 30WG (3.5oz/acre) were applied weekly. The number of plants in each plot with definite visual symptoms of whitefly-vectored geminivirus, primarily tomato yellow leaf curl virus (TYLCV), were recorded weekly beginning 19 Mar. The numbers of sessile nymphs (2nd and 3rd instars) and pupae (4th instar or red eye nymphs) of the silverleaf whitefly were counted on the terminal leaflet from the 7th to 8th leaf counting from the top of each of ten plants in the center row of each plot about weekly beginning on 31 Mar. Fruit were harvested on 4 Jun from the middle 10 plants of the middle row of check plots and plots treated only with either Admire or Platinum. Fruit with zippering, cat-facing or large blossom-end scars were culled as defective and counted and weighed. The remaining fruit were graded for size by machine where extra large fruit were > 2.75 inches in diam, large were 2.51 to 2.75 inches in diam, medium were 2.26 to 2.5 inches in diam and small were ≤ 2.25 inches in diam. All size categories were counted and weighed. Small fruit are considered too small for marketing and are culled.