Date of Award

Winter 2023

Project Type

Thesis

Program or Major

Animal and Nutritional Sciences

Degree Name

Master of Science

First Advisor

Anna K Wallingford

Second Advisor

Rebecca G Sideman

Third Advisor

Iago L Hale

Abstract

Spotted wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), is an economically important pest that damages small, soft-skinned fruits. Female spotted wing drosophila (SWD) have a heavily sclerotized, serrated ovipositor which allows them to lay their eggs in ripe and ripening fruits. Woven polyethylene weed mat has been reported to influence ambient temperature and relative humidity within blueberry canopies. There is a lack of context-specific evidence regarding the mechanisms impacting its efficacy and how it may interact with other control methods, like crop sanitizer sprays containing peroxyacetic acid (PAA) and hydrogen peroxide (HP).This study was a two-year, split-plot field experiment in which blueberries were harvested twice a week from spray treatment plots (PAA-HP and water) within plots with ground cover treatments (black weed mat, white weed mat, and grower standard woodchips). In 2022, both black and white weed mats reduced SWD infestation compared to the grower standard. In 2023, black weed mat was consistently effective in reducing infestation while white weed mat was not different from control plots in some weeks. There was no effect of the PAA-HP spray on reducing infestation but there were fewer adult female flies trapped in black weed mat plots that had been sprayed with PAA-HP in 2023. There were fewer adults captured in black weed mat plots compared to white weed mat and control plots. The mechanisms influencing the efficacy of weed mats were investigated by recording ambient temperature, relative humidity, and surface temperature within each ground cover plot. Larval photobehavior and the thermal tolerance of larvae was also explored to better understand how this life stage was potentially impacted by weed mats. No significant differences in air temperature or relative humidity were detected between ground covers. Black weed mat had significantly higher surface temperatures than white weed mat and woodchip surfaces regardless of full sun or overcast conditions. Larvae were shown to have low thermal tolerance, with fewer adults emerging from infested fruit that were exposed to temperatures above 30ºC. The choice assay provided evidence for photophobic behavior in third instar larvae, with more larvae choosing dark conditions over light conditions. These results indicate that third instar larvae may be making choices that affect their exposure to extreme temperatures. Overall, these results suggest that black weed mat may be an effective cultural control method for reducing infestation by SWD in blueberries. Based on the recorded abiotic conditions and observed larval behavior, this cultural control is likely acting on the larval life stage of SWD.

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