Efficacy of Insecticides Against Drosophila suzukii (Diptera: Drosophilidae) in Blueberries, 2014 *

The efficacy of formulation of malathion currently unregistered in blueberries, Atrapa, was compared with a standard malathion formulation and a recently registered material, Exirel for efficacy against SWD in May and June, 2014. Exirel treatments were compared with and without a surfactant. This experiment was conducted at the Horticultural Crops Research Station near Castle Hayne, NC in a planting of southern highbush blueberries, var. “Legacy.” Plots were 0.05 acres each and consisted of two rows of five plants. Treatments were replicated four times and arranged in an RCB design, blocked by rows, with a one-row untreated buffer in between blocks. Treatments ( Table 1 ) were applied using a CO ₂ pressurized backpack sprayer fitted with three solid cone nozzles (TeeJet TG 5 with medium size filter) calibrated to deliver a spray volume of 50 gpa at 45 psi pressure. Both sides of a row were treated to ensure full plant coverage. Applications began on 29 May and continued weekly for 3 wk.

SWD infestation in field grown fruit was measured by collecting 30 apparently undamaged berries per plot, approximately 7 d postapplication. Fruit were randomly collected from the center three plants in each plot and placed in plastic SWD rearing containers. Samples were brought back to the lab, weighed, and held for 7 d after which fruit were examined for infestation under a stereo microscope. Berries were weighed to determine if there were any impacts of the treatments on fruit size. Adult SWD monitoring traps (yeast, sugar, and water solution) were placed near the trial plots to determine local presence of SWD.

Because field infestation rates can be highly variable, semifield bioassays were also conducted to assess the performance immediately after treatment (0 DAT, acute activity) and 7 d after treatment (7 DAT, residual activity). Standard bioassay arenas, constructed from 32 oz. deli containers fitted with a floral water wick in the bottom, were used. An approximately 10-inch long stem and five sound appearing berries from each plot were collected from the middle bush in each plot and placed into each arena. In the laboratory, the berries were placed into a 1 oz plastic cup then placed back into the arena to prevent movement of the berries during the experiment. Five female and five male SWD, from a laboratory maintained research colony, were placed in each arena and mortality was assessed at three time points: 1, 3, and 5 d after infestation (DAI). Fruit from bioassay arenas were dissected to measure fly reproduction 7 DAI and the total number of live offspring (larvae plus pupae) were counted. All data were subjected to ANOVA via SAS PROC MIXED (v. 9.4), and means were separated using the LSmeans procedure. Treatment and replicated were considered independent variables.

Presence of Drosophila suzukii was low in the field throughout the experiment, with an average of two flies collected per monitoring trap per week. Similarly, field infestation was undetectable with no larvae found in any fruit. SWD mortality was higher in bioassays with treated materials as compared with the untreated controls ( Table 2 ). Mortality was higher in flies exposed to branches and fruit treated with the two Malathion formulations, Atrapa and Malathion 8F, than those from either Exirel treatment, with 90% of both adult male and female SWD dead within 1 DAI. The larval infestations in bioassay fruit followed a similar trend and was lower in the fruit treated with Atrapa and Malathion 8F ( Table 3 ).

The two malathion formulation had very slight residual effects, but Exirel and Exirel plus a surfactant appear to have some degree of residual activity ( Table 4 ). Both these treatments had higher mortality than either of the other treatments and the control in 7 DAT bioassays ( Table 5 ). There were also relatively fewer larvae recovered from these samples than from the other treatments and the control. The surfactant did not appear to improve either the initial efficacy of Exirel or the residual activity. There were no significant impacts of any treatment on the average berry mass ( Table 6 ).

Author notes