Host plant utilisation of two Dicraeus species (Diptera: Chloropidae) feeding on bamboo flowers

Bamboos are known for flowering simultaneously over a wide geographic range at long intervals of more than several decades. Florivory by Dicraeus phyllostachyus and D. nartshukae causes severe damage to bamboo seed production. However, the nature of the life history of the two Dicraeus species, particularly how they sustain populations during non-masting years of bamboos such as their host plant range, is poorly explored. We hypothesised that the two Dicraeus species host on other plant species and/or on non-floral organs of bamboos and move to bamboo florets during masting years. We tested whether the two Dicraeus species oviposit and develop on florets of grasses excluding bamboos (other grasses), and on non-floral organs of bamboos, including branch buds and bamboo shoots, by conducting a natural population survey and laboratory experiments. We found that the two Dicraeus species utilise short, slender shoots of Phyllostachys nigra var. henonis and a few other grass florets in the natural populations. Laboratory experiments also showed that the two Dicraeus species oviposited and fed on non-floral organs of bamboos and several species of other grass florets, although the oviposition rate and number of eggs varied among organs and the survival rate was low on most other grass florets. The generalised feeding ability may have enabled the two Dicraeus species to utilise the bamboo florets during masting years and become the dominant florivorous insect of bamboos. Unravelling their life history strategies may contribute to understanding adaptation in florivorous insects of masting plants as well as their impact on the evolution of masting in plants.