Insects have adapted to a wide variety of resources and habitats, making them the most species-rich and ecologically successful taxa in terrestrial ecosystems. Recent studies integrating extensive sampling with DNA barcoding have revealed remarkable diversity within the family Cecidomyiidae (Diptera). This family not only exhibits extraordinary species richness but also encompasses a broad array of feeding habits. Understanding the mechanisms underlying this diversity is essential for elucidating insect diversification and ecological adaptation.
Among Cecidomyiidae, some mycophagous species display an unusual reproductive strategy known as paedogenesis, in which the ovaries develop inside a “mother larva” or “mother hemipupa,” and offspring larvae are produced through ovoviviparous parthenogenesis. These paedogenetic species are able to shift their reproductive mode and complete holometabolous development to emerge as adults. However, the factors triggering this shift remain poorly understood. Identifying these factors is crucial for clarifying both the adaptive significance of paedogenesis and the evolutionary processes shaping cecidomyiid diversification.
In this study, we conducted rearing experiments to investigate the factors underlying reproductive mode shifts using a Flammulina velutipes mycelial medium routinely employed in our successive-generation rearing system. In this system, paedogenetic larvae are maintained over multiple generations by transferring them onto fresh mycelial media every few weeks. During the procedures, we occasionally observed adult emergence from old media that remained after larval transfer. These observations led us to hypothesize that the degree of desiccation of the mycelial medium may influence reproductive mode shifts.
To test this hypothesis, we used the paedogenetic gall midge Mycophila speyeri. PDA media inoculated with F. velutipes mycelia were cultured for 10 days, and larvae were then transferred onto the media. The media were assigned to either a desiccation treatment or a control group. The number of adults emerging within one month after larval transfer was significantly higher in the desiccation treatment group. These results indicate that desiccation is likely to influence reproductive mode shifts in M. speyeri. In this presentation, we will further discuss factors associated with reproductive mode shifts in mycophagous paedogenetic gall midges, incorporating additional data from rearing experiments using other species.