Abstract
The invasive pest fruit fly Drosophila suzukii is thought to be a specialist on healthy, i.e. unwounded, non-fermenting fruits. Morphological (sharp ovipositor) and neurophysiological/behavioural adaptations have been suggested to contribute to distinct adult feeding (wounded/microbe-laden fruits) and reproductive (healthy fruits) sites. We tested whether (1) variation in the overall availability of fruits, (2) variation in fruit type (healthy, wounded, fermenting), and (3) the relative abundance of different fruit types are ecological determinants of D. suzukii egg-laying decisions. Even though individual flies reduced their reproductive output when resource availability (blueberries) was low, a significantly higher proportion of eggs was allocated to healthy fruits, relative to wounded and fermenting fruits. However, the preference for healthy over wounded fruits declined continuously with a decrease in the relative abundance of healthy fruits and the overall reproductive output did not change. Under laboratory conditions, D. suzukii larvae achieved a higher developmental success on wounded than on healthy blueberries, but suffered less from density-dependent competition in healthy fruits. These data suggest that D. suzukii, despite showing an egg-laying preference for healthy fruits, also uses wounded/fermenting fruits as egg-laying sites, and that it may thrive well in windfall fruits.
Highlights
Drosophila suzukii reveals a flexible preference for oviposition into healthy fruits Renate Kienzle, Lara B
The proportion of eggs individual D. suzukii females laid into healthy blueberries did not depend on resource availability (Type II ANOVA, p = 0.470) nor was it influenced by the total number of eggs the females deposited (Type II ANOVA, p = 0.745)
The overall proportion of eggs laid into healthy fruits was 0.565 ± 0.381 s.e., that is D. suzukii females laid a significantly higher proportion of eggs into healthy fruits than the 1/3 ratio expected under the null hypothesis (GLM estimate: 0.867 ± 0.162 s.e., t-value: 5.363, p < 0.001), whereas wounded fruits received the significantly lowest proportion of eggs, and seem to be the least preferred oviposition sites (Fig. 2)
Summary
Drosophila suzukii reveals a flexible preference for oviposition into healthy fruits Renate Kienzle, Lara B. We tested whether (1) variation in the overall availability of fruits, (2) variation in fruit type (healthy, wounded, fermenting), and (3) the relative abundance of different fruit types are ecological determinants of D. suzukii egg-laying decisions. Even though individual flies reduced their reproductive output when resource availability (blueberries) was low, a significantly higher proportion of eggs was allocated to healthy fruits, relative to wounded and fermenting fruits. D. suzukii larvae achieved a higher developmental success on wounded than on healthy blueberries, but suffered less from density-dependent competition in healthy fruits These data suggest that D. suzukii, despite showing an egg-laying preference for healthy fruits, uses wounded/fermenting fruits as egg-laying sites, and that it may thrive well in windfall fruits. At higher fruit densities we expected females to oviposit more often into the presumably non-preferred decay stages (wounded/fermenting fruits), which leads to a random distribution of eggs across all fruit categories. In a third experiment we examined potential fitness consequences of an oviposition preference, and provided a first test of the developmental success of D. suzukii larvae in healthy and wounded blueberries
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