Biological Observations on the Scolytid Ambrosia Beetles, Tea Root Borer, Xyleborus germanus BLANFORD and Tea Stem Borer Xyleborus compactus EICHHOFF

Abstract

1. Artificial culture of the ambrosia fungi.Xyleborus germanus and X. compactus fungi develop mycellia very actively but produce spore very poorly in artificial culture media, in which fresh wood containing medium proved, better. However, when the female beetles bore into the artificial media with ambrosia fungi, the spore formation is observed along the way of galleries, it is, therefore, clearly suggested that the spore formation is promoted by the component of saliva or unknown secreted substances of the beetles. The larvae feed on myceilium as well as spore.With potato agar media in a test tube, the fungi grow better in plate culture than in slant culture. The optimum temperatures of the fungi development are about 23°C. in X. germanus and about 26°C. in X. compactus.2. Artificial rearing of ambrosia beetles.X. germanus can be reared in the artificial culture throughout whole generation of the beetles.Fresh tea roots (1-1.5cm. in diameter) are cut 2-3 cm. in length and about 100g. of the material are put in 300 ml. Erlenmyer flasks, the flasks are stoppered with cotton plugs and are steam-sterilized in an autoclave. After sterilization, pieces of isolated fungi are inoculated aseptically into the flask and incubated at 23°C. for about 10 days.When the mycellium of fungus covers the culture medium, 2-3 adult female beetles are introduced into the flask without sterilization. In the flask, ambrosia fungus grows vigorously and can suppress the development of all extraneous fungi, so that the beetles can be reared throughout 1-2 generations in the laboratory.The female beetles immediately make new galleries and the spore of fungus is formed in the root. Ten or twelve days after invasion, eggs are laid and 2-3 days thereafter larvae are hatched out. The development of the beetles can be observed from outside of the flask.X. eompactus can not be reared similarly to X. germanus as described above.3. Biological observation of Xyleborus germanus.In neighbouring Makinohara tea plantation (200 m. high above the sea level), X. germanus occurs 2 times a year and overwinters in roots forming colony of several broods at adult female stage.The optimum temperature range of rearing is 21-23°C. and over 25°C. a majority of beetles is dead in the laboratory culture.The first generation period occurs from June to July and the population increases at maximum rate. The second generation period occurs in September, from July to August the beetles spend in adult female stage and the population is lowest throughout the year.The adult female beetles prefer to bore into tea roots (1-1.5 cm. in diameter) at about 30 cm. depth under ground and sometimes into tea twigs.A female lays about 30 eggs, at one time 10 eggs on the wall of ambrosia fungus. It takes 30-49 days at the controlled temperature of 23°C. from the entry of a female to the emergence of the successive adult female.4. Biological observation of Xyleborus compactus.X. compactus occurs 2 times a year and overwinters in twigs at adult female stage.The first generation occurs from July toAugust and the second from August to September.Surroundings of attacked parts in living stems become brownish discolored and cause die-back.The female beetles prefer to bore into slender branches (5-8 mm. in diameter) under the bush surface, but in a high population, they bore into big trunks contacted on the ground level.The optimum temperature range of rearing in the laboratory is 25-27°C.A female lays 12-15 eggs in a gallery and it takes 25-27 days from the entry of a female to the emergence of the successive adult female.