Females invest more energy in flight: flight characteristics of Platypus quercivorus (Murayama) revealed by a flight mill

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ABSTRACT Dispersal flight is an essential component of the life history of bark and ambrosia beetles. Previous studies have shown considerable variation in flight distance between individual beetles; however, different factors drive this variation between species. Furthermore, when the ecological role of dispersal flight differs between sexes (i.e., males locate hosts and females follow), influencing factors might also vary. Here, we evaluated the factors driving variation in the dispersal flight distance of the ambrosia beetle Platypus quercivorus (Murayama) (Coleoptera: Curculionidae: Platypodinae), which is a vector insect of Raffaelea quercivora, the causal agent of the Japanese oak wilt, and we estimated sex-based differences for each influencing factor. A flight mill was used to measure flight distance, flight duration, and initial and terminal flight speed. Because flight speed was not constant during beetle flight, we estimated both initial and terminal flight speed, and assumed that initial flight speed represents a relative measure of energy allocated to flight. Flight distance was mainly determined by flight duration, with an average flight speed of 4.22 km/h for both sexes. Initial and terminal flight speed affected flight distance; however, these factors had contrasting effects between sexes. Specifically, a simultaneous increase in initial and terminal flight speed by males increased flight distance. In comparison, increased flight distance by females was mainly achieved by increasing the initial flight speed. These different patterns in increased flight speed likely reflect differences in the relative importance of flight in the life history of the two sexes.