Drosophila suzukii preferentially lays eggs on spherical surfaces with a smaller radius

Abstract

Drosophila suzukii is an agricultural pest that predominantly harms small fruits, having a serrated ovipositor that is able to pierce the skin of ripening fruits. Its oviposition preference has been studied from various aspects including chemical and physical properties of oviposition substrates. However, its preference for certain shapes or sizes of substrates has not been explored. In this study, we tested the oviposition preference of D. suzukii for artificial oviposition substrates with different surface curvatures using 27 strains recently established from wild populations collected in Japan. We found that D. suzukii laid more eggs on a surface with smaller radii (4.8 and 5.7 mm) compared with larger radii (7.7 and 9.6 mm). We also found that the most preferred radius differed among strains. Notably, the preference was independent of the volume of substrates, suggesting that D. suzukii uses the surface curvature as a cue for its oviposition site selection. These results provide an additional explanation for why D. suzukii preferentially uses small fruits as its oviposition sites.

Figure 1

Schematic representation of the experimental setups. (A) Shape of the oviposition substrates. (B) Arrangement of the oviposition substrates in the oviposition assay. In a disposable petri dish, a piece of cotton pad was placed and soaked with water. Eight oviposition substrates were put on the cotton pad. “L” in two-choice assay designates oviposition substrates with either of 5.7, 7.7, or 9.6 mm radius.

Figure 2

Results of the four-choice assay. The proportion of the number of eggs on each size of substrates to the total egg number on all substrates was plotted. Each point represents a single replicate. Ten replicates were made for each of the 27 strains, in total 270 times of assay were conducted. Dotted lines indicate the proportion of 0.25, the expected value of the null hypothesis (no preference). Shading represents the range of proportion between the upper and lower quartiles that contains 50% of data.

Figure 3

Strain-wise plot of the results of the four-choice assay. Proportion of eggs laid on each size of the oviposition substrate to the total egg number is shown. The assay was repeated for 10 times for each strain.

Figure 4

Results of the two-choice assay. (A–D) D. suzukii strains #17, #20, #22, and #26, respectively. (E) D. melanogaster CS. The x axis indicates the radius of the larger substrates. The smaller substrates were fixed as 4.8 mm. Preference index = (Number of eggs laid on smaller substrates − Number of eggs laid on larger substrates) ÷ Total egg number. Positive values of the preference index indicate the preference for a smaller radius.