Effect of Foliar Application of Xxpire on Bemisia tabaci (MED Whitefly) and Amblyseius swirskii, 2016* Open Access

With the overall goal to integrate predatory mite Amblyseius swirskii in the management program of MED whitefly, the specific objective of this study was to evaluate Xxpire, a premixed formulation of spinetoram and sulfoxaflor for whitefly control, and assess its compatibility with swirskii mite. The trial was conducted on an ornamental host, Salvia nemorosa L. (New dimension blue) under greenhouse condition at U.S. Horticultural Research Laboratory (USHRL). Salvia plants were grown from seed in Premier Pro-mix General Purpose Growing Medium in seedling trays (72 wells), and placed inside plexiglass screened cages (61 cm × 91 cm × 61 cm) for ∼8 wks to prevent contamination prior to experimentation. Plants from seedling trays were then transplanted into one-gallon plastic pots and placed in mesh screened cages (61 cm × 61 cm × 61 cm). Potted plants were irrigated as needed and fertilized with 50 ml/pot of Peters Professional^® 20-10-20 (325 ppm) (Scotts Co., Marysville, OH) once every week. Four treatments—(1) control, (2) Xxpire, (3) swirskii, and (4) swirskii + Xxpire were arranged in a randomized complete block design with six replicates, where each replicate (cage) consisted of four plants per cage. Salvia plants were inoculated with MED whitefly by releasing 100 adults per cage (25 per plant) three times at weekly intervals. Treatment cages with swirskii mite were inoculated with 20 mites/plant (3×) starting one week after first whitefly inoculation and prior to insecticide application. Pretreat counts of whitefly and mites and whitefly biotype confirmation was made prior to the foliar application of Xxpire. Treatment evaluation was made at weekly intervals for a period of 7 wk by destructive sampling five leaves per replicate (cage) and recording the number of A. swirskii eggs and motiles (nymph + adult) per leaf, and MED whitefly eggs and nymphs on two discs (∼1 cm²) per leaf, using a binocular microscope. Whitefly adult count was taken per leaf sample by leaf-turn method (visual counting of adults before removing leaves from the plant). Counts of whitefly and swirskii mite observed in different treatments were analyzed independently using a generalized linear mixed model with the SAS (SAS Institute, Cary, NC) procedure GLIMMIX. The model was used to determine the effect of insecticide treatments, sampling period and their interaction on the arthropod counts. Since the response variable was count data with no upper bound, in model statement distribution was specified as Poisson. The autoregressive correlation structure was applied to take care of the correlation between observations collected on the same experimental units over time. Differences among treatment means were separated using Fisher’s LSD test (α = 0.05) in the repeated measures model. As the number of whitefly life stages in the efficacy trial was not uniform, Henderson–Tilton’s formula was used to calculate corrected mortality.

In mite only treatment, a significantly higher mean number of A. swirskii eggs on wks 1, 4, 5, 6 and motiles on wks 1, 2, 4, 5, 6 were found compared to rest of the treatments (Table 1). In the combination treatment (A. swirskii + Xxpire), A. swirskii eggs and motiles were observed sporadically on different sampling weeks, and mite counts were not significantly different from the control. Xxpire was effective in suppressing MED whitefly life-stages during the study period. In the insecticide only treatment, a significantly lower number of whitefly eggs and nymphs were recorded (compared with the untreated control) on wk 3–6 and 2–6, respectively (Table 2). A. swirskii was also effective in reducing whitefly eggs (except for wk 2 and 7), and immatures (except for wk 7) on different sampling weeks. Suppression of various stages of whitefly in combination treatment, was similar to Xxpire and A. swirskii applied alone, except for wk 5 for whitefly eggs and wk 4 for nymphs (Table 2). Combination treatment provided significant reduction whitefly adults on all the sampling dates except for wks 4 and 6. Overall whitefly mortality in different treatments ranged between 35 and 85% (wk 1–wk 6) for A. swirskii, 36–96% for Xxpire, and 44–91% (wk 1–wk 6) for the combination treatments. Based on the insecticide efficacy results, we speculate that the low whitefly (prey) count (lack of sufficient food) and/or the incompatibility of the insecticide may have resulted in reduced population of A. swirskii in the combination treatment. No phytotoxicity was observed for any treatment.

Author notes