Overwintering of spotted wing drosophila in Ontario - 2012-2013

Spotted wing drosophila (Drosophila suzukii) is a recent invasive tender fruit and berry pest in Ontario. Unlike other fruit flies, female SWD are able to lay eggs in ripening fruit. The developing larvae destroy fruit and introduce secondary rots before harvest. To improve management of this pest more knowledge about its biology and ecology is needed.

Little is known about the ability of spotted wing drosophila to overwinter in Ontario. It has been suggested that cold winter temperatures exclude the possibility of winter survival in fields, and that yearly infestations are due to winter survival in warmer, man-made habitats or from seasonal dispersal and re-infestation. However, infestations of spotted wing drosophila last year as far north as Quebec and its ability to survive cold winters in its native Japan seem to indicate overwintering potential.

High captures of spotted wing drosophila in Ontario in summer of 2012 may have been due to mild winter temperatures in 2011-2012. Therefore, in winter 2012-2013 we assessed the potential of spotted wing drosophila to overwinter in forested field edges where there are alternate wild hosts and abundant leaf litter and under row covers in fields

Near Vineland ON, flies were captured until Dec. 21, 2012 and again during the week of Jan. 11-18, 2013 (Fig. 1A). No flies were captured from Dec. 22 - Jan 10 or after Jan. 18. Near Halton Hills, traps were set-out during periods of relatively warmer weather, and flies were captured during each of the three trapping periods (Fig. 1B). At both sites there is a trend towards capturing more flies in the forest edge and fewest flies in the field centre (Fig. 1). At the end of November, none of the trapped females were carrying eggs, which is the normal state in which they pass the winter. Over the course of the winter, possible overwintering sites such as leaf litter, row covers, plastic tunnels and a greenhouse were sampled for spotted wing drosophila, but none were found after Jan. 18.

Trapping for spotted wing drosophila will continue in spring 2013 at these and other locations to detect when flies are first active and whether captures are higher initially in forest edges. Determining the overwintering habitats and early season flight patterns of spotted wing drosophila will help develop better management tools, particularly if edge based controls can be used to reduce populations and damage to fruit.

Figure 1. Mean numbers of spotted wing drosophila captured in traps placed in and around fields near Vineland ON

Figure 1. Mean numbers of spotted wing drosophila captured in traps placed in and around fields near Halton Hills ON

Figure 1. Mean numbers of spotted wing drosophila captured in traps placed in and around fields near Vineland ON (A) and Halton Hills ON (B) during late 2012 and early 2013. There were no flies captured Dec. 22 - Jan. 10 in Vineland. The means of the daily maximum and minimum temperatures during each trapping period are shown.


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