Maternal effects increase survival probability in Drosophila subobscura larvae

Drosophilid flies breeding on ephemeral resource patches (e.g., decaying fruits) are assumed to transfer yeasts to their oviposition sites, presumably in order to positively affect offspring development. We tested this hypothesis with Drosophila subobscura Collin (Diptera: Drosophilidae) by manipulating their nutritional (yeast-fed vs. non-yeast-fed) and reproductive status (mated vs. non-mated). Flies were then released into vials containing decaying fruits (either sloes, crab apples, or Syrian plums). After a constant residence time in the vials, the flies were removed, 16 first-instar larvae were transferred to the fruits and their survival probability to the adult stage was recorded. Whereas previous exposure of the larval substrate to yeast-fed males and virgin females (yeast-fed and non-yeast-fed) had no effect on survivorship, exposure to yeast-fed and mated females that deposited eggs on the fruits (subsequently removed) led to a significant increase in the survival probability of the transferred larvae to the adult stage. Although the exact mechanism of yeast transmission remains to be determined, we suggest an active inoculation of the breeding substrates with yeast by ovipositing females. In agreement with previous studies, we found a negative effect of mould growth on larval survival, which, however, depended on the fruit type. We discuss various scenarios of yeast involvement in benefits to the insect larvae and suggest that insect-mould interactions should be examined in detail in order to better understand the behavioural and life-history traits of insects that depend on ephemeral resources.