Control of Bemisia tabaci (MED whitefly) on Saliva, 2018

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 afidopyropen, a pyropene insecticide 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 and placed inside Plexiglass-screened cages (61 × 91 × 61 cm) for ~8 wk to prevent contamination prior to experimentation. Plants in seedling trays were then transplanted into 1-gal plastic pots and placed in mesh-screened cage (61 × 61 × 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). Four treatments—1) control, 2) afidopyropen, 3) swirskii, and 4) swirskii + afidopyropen 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 1 wk after first whitefly inoculation and prior to insecticide application. Plants in cages were sampled to obtain pretreatment counts and to confirm whitefly biotype. Foliar application of afidopyropen was made at the recommended rate of application (7 fl oz/ 100 gal) using a handheld sprayer. 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 Fisheris 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.

Weekly samplings showed overlapping generations of A. swirskii on host plants in combination treatment (A. swirskii + afidopyropen) throughout the study period, indicating that foliar application of afidopyropen at the applied rate was compatible with A. swirskii. No significant difference in A. swirskii eggs and motiles between mite treated and combination treatment was reported on any of the sampling dates (except week 1; Table 1). In afidopyropen treatment, a significantly lower number of whitefly eggs, nymphs, and adults compared with the untreated control was recorded throughout the study period (Table 2). Amblyseius swirskii releases were as effective as afidopyropen treatment in suppressing the number of whitefly, and numerically, combination treatment provided the best suppression in MED whitefly population. Overall whitefly immatures (eggs + nymphs) mortality in different treatments during 7-wk period, ranged between 65 and 100% (mean mortality = 85%) for A. swirskii, 92–98% (mean mortality = 95%) for afidopyropen, and 93–100% (mean mortality = 99%) for combination treatments. No phytotoxicity was observed for any treatment.

Funding

This research was supported by the Floriculture and Nursery Research Initiative and USDA Farm Bill.