SWD series #1
Most spotted-wing drosophila (SWD) that survive the winter do so as adult females. Winter morph females mate during fall, store the sperm over winter, and infest the first ripening fruits in early spring. As temperatures fall below 50°F (10°C), few SWD females carry eggs and the population decreases. When temperatures rise above 50°F (10°C) for periods longer than five days, the fertilized eggs within SWD females start to mature and the population begins to increase above the overwintering level (see Figure 1, page 2).
When temperatures reach 64°F (18°C), adult females lay more eggs (Figures 1 and 2, page 2). Eggs hatch into larvae, which develop into pupae and then adults at increased rates as temperatures climb during the summer. As the season progresses, it is possible for the generations to overlap, resulting in a relatively stable distribution among different life stages (egg, larva, pupa, adult). In Oregon, approximately 90% of all life stages are eggs, larvae and pupae during this period, with only 10% in the adult life stage (Figure 3, page 2).
One reason SWD is so difficult to manage is that eggs, larvae and pupae are well protected within the fruit or in the soil. Also, a steady stream of adults reaches reproductive maturity and attacks the crop. When average daily temperatures drop below 50°F (10°C) or increase above 82°F (28°C), SWD become less active and reproduce at lower rates. However, the insect can optimize its behavior to daily temperature cycles. During hot summer periods, the majority of activity, including egg-laying, occurs during the cooler dusk and dawn periods (Figure 4).
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This publication is one of a series of nine publications focused on strategies for controlling spotted-wing drosophila in Oregon. Find them at https://catalog.extension.oregonstate.edu/. The publications in this series include: