Cannibalism and potential predation in larval drosophilids

1. Although yeast encompasses the major food source of Drosophila melanogaster, a recent study demonstrated that D. melanogaster larvae can complete their development on an exclusively cannibalistic diet. If cannibalism is an adaptive behaviour under nutritional stress, not only conspecific larvae but also allospecific larvae could be the target of predation. Under natural conditions, stings of parasitoids can cause a larval injury that attracts cannibalistic larvae, however, the effect of parasitism on larval cannibalism has never been investigated in drosophillids. 2. Here, we investigated the cannibalistic and predatory behaviour of four frugivorous Drosophila species (Drosophila simulans, D. melanogaster, Drosophila auraria, Drosophila triauraria) towards the conspecific or allospecific source of attraction (SOA) larvae. We also investigated their attraction to parasitised conspecific SOA larvae. 3. The present study demonstrates that the cannibalism observed previously could be potentially extended to predation in D. simulans and D. melanogaster, leading to intra-guild predation that has not been previously observed. Although D. auraria and D. triauraria were not significantly attracted to conspecific SOA, some level of attraction was suggested for allospecific SOA. In agreement with this, larvae of these species did not complete their development to adulthood when reared on an exclusively cannibalistic diet. The injury inflicted by parasitoid wasps was shown to attract cannibals in some cases. 4. The current results indicate that cannibalistic behaviour might not be a general feature in drosophilids. The environmental conditions or selective pressure that drives the evolution of cannibalism within this group should be a target of future studies.