Effect of Temperature and Genetic Inheritance on the Number of Mycangium Pits in Female Platypus quercivorus (Coleoptera: Curculionidae: Platypodinae)

Ambrosia beetle Platypus quercivorus is a vector of Japanese oak wilt. Only females possess 4−12 mycangial pits on the pronotum, which are essential for carrying symbiotic fungi and are thought to be a significant determinant of beetle fitness. However, the factors influencing the pit numbers remain poorly understood. To elucidate the effects of environmental conditions and parental traits on the pit number, we conducted a controlled breeding experiment. Collected P. quercivorus broods were categorized into three groups (large, middle and small) based on their average number of maternal mycangial pits. Excluding the middle groups, male−female pairs from the same group (large or small) were inoculated into Quercus crispula logs and incubated under four temperature regimes: 18, 22, 26, and 30 °C. We analyzed offspring pit number and body weight relative to temperature and parental traits. Both traits increased at lower temperatures likely because accelerated metabolism and developmental rates at higher temperatures, reduces the time and resources available for body growth and pit development. Notably, the traits exhibited distinct inheritance patterns: offspring pit number was significantly influenced by maternal pit number but not by the body weight of either parent. In contrast, offspring body weight was significantly correlated with maternal pit number, paternal body weight, and maternal body weight. Thus, we conclude that temperature plays a critical role in shaping these traits. Parental effects indicate that both mycangium pit number and body weight are heritable in P. quercivorus. However, their distinct inheritance patterns suggest a weak genetic association between the traits, implying that they may evolve largely independently.