Time-dependent oviposition deterrence by an oviposition mark in a fungus-farming lizard beetle

Abstract

In insects, the selection of a suitable oviposition site is critical for offspring performance. Avoiding hosts already occupied by conspecific immatures in oviposition is one of the mechanisms to reduce intraspecific competition. The avoidance of such hosts by ovipositing females has been well-documented in parasitoid wasps and phytophagous insects but remains unknown in mycophagous insects. Here, we report that oviposition marks (OMs) of the fungus-farming lizard beetle, Doubledaya bucculenta (Coleoptera: Erotylidae: Languriinae), deter conspecific females from oviposition. The females excavate a wall of host bamboo internodes to access cavities for oviposition and plug the holes with excised bamboo fibers after oviposition. A larva completes its development within a single internode. To determine what types of OMs function as oviposition deterrents and how the oviposition-deterring pattern associates with offspring survival, we examined the oviposition behaviors, egg-period lengths, and reactions of larvae to eggs. When a single internode was provided, most females laid eggs in internodes with no OMs, incomplete OMs, or plug-removed completed OMs (COMs), but fewer females laid in internodes with fresh COMs and no females laid in those with old COMs. When eggs were reared under constant temperatures, egg-period lengths varied, suggesting that later-laid eggs sometimes hatch earlier than earlier-laid eggs. When a larva encountered an egg, all eggs were killed shortly. These results suggest that the females avoid internodes associated with high offspring mortality and that the COM’s plug contains an oviposition-deterring cue. Given that larvae of oviposition-deterring insects including D. bucculenta inhabit spatiotemporally-limited sites and have limited mobility, high resource competition in the larval stage may have driven the evolution of oviposition deterrence.