Intraspecific Competition May Drive Resource Use Diversity in Drosophila suzukii

Intraspecific competition can increase resource use diversity within natural populations and may favor individuals who are willing to accept a wider range of hosts and/or host qualities. Drosophila suzukii (Matsumura) is a highly polyphagous, invasive vinegar fly that severely threatens berry and cherry production in North America, Europe, and South America. To determine if intraspecific competition affects D. suzukii host use and population growth, we compared oviposition and infestation patterns in ripe and unripe blackberries, a highly preferred host, as fly numbers increased in an unmanaged research planting with a history of high D. suzukii infestation. We hypothesized that females would oviposit in unripe berries, which are suboptimal hosts compared to ripe berries, as levels of intraspecific competition increased. We haphazardly collected 20 ripe berries and secured drawstring mesh bags over 20 purple, red, and green-pink berries, and deployed traps to catch adults, weekly in June-August 2015. Infestation occurred first in ripe berries, whereas unripe berries were infested only after the number of female D. suzukii caught in traps increased sharply. These results suggest that intraspecific competition affects D. suzukii host use and population growth, and may help growers better time management treatments and more effectively manage D. suzukii populations.