Reduced Drosophila suzukii Infestation in Berries Using Deterrent Compounds and Laminate Polymer Flakes

Abstract

Drosophila suzukii (Matsumura) is a recent invasive pest of soft fruits in North and South America and Europe. Control relies on frequent applications of synthetic insecticides. Additional tactics are needed for development of an effective integrated pest management program. Study objectives were to evaluate the repellency and oviposition deterrent capability of compounds in plant essential oils and the effect of select compounds on infestation rates in strawberries, using laminate polymer flakes as a carrier. Of 14 compounds from 5 essential oils, thymol was the most repellent to adult D. suzukii males and females for up to 24 h in the laboratory. Citronellol, geraniol and menthol were moderately repellent. In a choice assay, thymol on cotton wicks adjacent to ripe raspberries reduced female fly landings and larval infestation levels. In a no-choice assay, thymol reduced female fly landings by 60%, larval infestation by 50% and increased fly mortality compared to controls. Neither citronellol alone nor a blend of four repellent compounds was as effective as thymol alone at reducing fly landing, larval infestation, or increasing fly mortality. In a choice assay using polymer flakes, larval infestation was greater in raspberries near untreated flakes than in raspberries near flakes treated with thymol or peppermint oil. In the field, thymol and peppermint flakes reduced larval infestation levels by 25% in strawberries at 4, but not 7, days after application, compared to untreated flakes. With future improvements in application strategies, deterrent compounds may have a role in improving the management of D. suzukii.

Keywords: citronellol; essential oils; peppermint; repellents; spotted wing drosophila; strawberry; thymol.

Figure 1

Percentage of male Drosophila suzukii on cotton wicks with blueberry (filled bars) or blueberry juice + repellent compound(s) (empty bars) at 2, 6 and 24 h after start of experiment. Oils applied at 10 mg/cotton wick, individual compounds at the proportion in which they occurred in the oil (i.e., citronella at 3.4 mg/wick), and blends at the sum of the proportions of individual compounds. Significant differences (G-test): *** (p < 0.001), ** (p < 0.01), * (p < 0.05), ‘NS’ no significant difference (p > 0.05).

Figure 2

Percentage of female Drosophila suzukii on cotton wicks with blueberry (filled bars) or blueberry juice + repellent compound(s) (empty bars) at 2, 6 and 24 h after start of experiment. Oils applied at 10 mg/cotton wick, individual compounds at the proportion in which they occurred in the oil (i.e., citronella at 3.4 mg/wick), and blends at the sum of the proportions of individual compounds. Significant differences (G-test): *** (p < 0.001), ** (p < 0.01), * (p < 0.05), ‘NS’ no significant difference (p > 0.05).

Figure 3

Number of female Drosophila suzukii flies landing at 6 h and 24 h after the start of the experiment on (a,b) and number of larvae recovered in (c) raspberries next to cotton wicks treated or not treated with repellent compounds. Significant differences (G-test): *** (p < 0.001), ** (p < 0.01), * (p < 0.05), ‘NS’ no significant difference (p > 0.05).

Figure 4

Number of female Drosophila suzukii flies landing on (a,b), number of dead flies on (c) and level of larval infestation in (d) raspberries next to cotton wicks either treated or not treated (control) with repellent compounds. Means with the same letter in each panel are not significantly different, Tukey’s HSD test (p > 0.05).

Figure 5

Release rate (%w/w) of thymol and peppermint oil formulated Bio-flakes^® at 30 °C. Non-linear regressions fitted to the data.

Figure 6

Location of female Drosophila suzukii flies in arenas at 2, 6, 10 and 22 h when Bio-flakes^® treated with either peppermint oil or thymol were compared to untreated Bio-flakes^® and placed in Petri-dishes below raspberries.

Figure 7

Numbers of Drosophila suzukii larvae recovered in raspberries near Bio-flakes^® treated or not treated (blank) with repellent compounds in a laboratory choice bioassay. Significant differences (G-test): *** (p < 0.001).

Figure 8

Mean (±SE) numbers of drosophilid larvae per gram of strawberry or per strawberry. Strawberries were picked 8 (a,b) or 11 (c,d) September 2014 from plots treated 4 September with untreated or thymol or peppermint treated (10% w/w) Bio-flakes^®. Means with the same letter in each panel are not significantly different, Tukey’s HSD test (p > 0.05).