Resource use by individual Drosophila suzukii reveals a flexible preference for oviposition into healthy fruits

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.

Figure 1

Experiment 1 – Total number of eggs laid per female as a function of total resource availability, i.e. in total 3, 9, 18 or 30 fruits. The line depicts the results of the generalised linear regression model (see Supplementary Table S1). For better visibility data are staggered around the actual number of fruits.

Figure 2

Experiment 1 – Proportion of eggs allocated to healthy (blue), wounded (dark blue) and fermenting (yellow) fruits, as a function of resource availability, i.e. in total 3, 9, 18 or 30 host fruits. The proportion of eggs deposited differed significantly between wounded and fermenting fruits (Wilcoxon signed rank test on arcsine square-root-transformed proportions; p = 0.0102).

Figure 3

Experiment 1 – Proportion fruits used as oviposition sites, independent of the total number of eggs deposited per fruits, as a function of healthy (blue), wounded (dark blue) and fermenting (yellow) fruits, and resource availability, i.e. in total 3, 9, 18 or 30 host fruits. (see Supplementary Tables S3 and S4 for more information).

Figure 4

Experiment 2 – Proportions of eggs allocated to healthy fruits as a function of different proportions of healthy and wounded fruits but otherwise constant total fruit availability. The dashed grey line depicts the average allocation of eggs under the null hypothesis, the blue line the results of logistic generalised linear regression model. For better visibility data are staggered around the actual number of fruits.

Figure 5

Experiment 3 – Egg-to-adult survival (A), development time (B) and adult dry weight (C) of D. suzukii that developed at different densities (eggs per mg blueberry) in healthy (blue, n = 111) or wounded (dark blue, n = 111) blue berries. Lines depict the most parsimonious GLM regression models (see Supplementary Tables S6 and S7). In C, triangles and crosses represent female and male body weight, respectively. Dashed lines depict regression models for male weight.