Bet-hedging strategies in gall-inducing insects: Daphnephila gall midges (Diptera: Cecidomyiidae) exhibit quadrimodal adult emergence through two types of polymodality in Taiwan

Abstract Daphnephila gall midges (Diptera: Cecidomyiidae) inhabiting subtropical evergreen forests in Taiwan exhibit complex temporal diversification in their life histories. We conducted a 7-year field study (2004–2011) tracking four leaf-galling Daphnephila species on 105 Machilus thunbergii trees in northern Taiwan, integrating host phenology, gall development, adult emergence, and parasitism. The host tree displays bimodal bud flushing, producing winter and spring leaf cohorts that provide extended oviposition windows. Correspondingly, Daphnephila populations exhibit quadrimodal adult emergence generated by two forms of polymodality. Within a single generation, individuals display intraseasonal polymodality (Type A sensu Waldbauer 1978), emerging in both winter and spring. In addition, a proportion of larvae undergo extended diapause exceeding 1 year, corresponding to interannual polymodality (Type C). Offspring from the same female frequently diverged into univoltine and semivoltine pathways, demonstrating flexible life-history expression. Parasitism rates were significantly lower in winter-emergent individuals and in semivoltine cohorts, supporting enemy avoidance as a major driver of temporal diversification. This study represents the first explicit documentation of Type A polymodality in Cecidomyiidae and reveals a multi-layered bet-hedging strategy operating across seasonal and interannual scales in a subtropical gall-inducing insect system.