Reproduction of the ambrosia beetle, Xyleborus pfeili (Ratzeburg) (Col., Scolytidae), on semi-artificial diet

Abstract: Reproduction of the ambrosia beetle Xyleborus pfeili (Ratzeburg), in relation to galley formation, was examined by artificial rearing in test tubes. Unmated females produced only male offspring, while broods that originated from fertilized females had strongly female-biased sex ratios. Thus, the reproductive process of X. pfeili is arrhenotokous parthenogenesis. Oviposition took place over a long time, as eggs were present in the tunnels throughout the experiments (up to 40 days after inoculation). Total length of a gallery system and number of offspring per tube were positively correlated. Pupation and eclosion of males were later than those of some females. In the case of two males (offspring in pupal and/or adult stages) in the same gallery system, most of the males coexisted in the condition of both different stages and different branch tunnels. These results imply that a mother beetle of X. pfeili determines the number of her eggs in response to the size of each branch tunnel (= amount of ambrosia fungus), and produces at least one male egg in the tunnel after laying some female eggs.