Biological notes on Xanthochroa waterhousei Harold (Oedemeridae) : Studies on poisonous beetle, II

Abstract

1. A series of investigations have been made on the bionomics and life history of the dermatitiscausing beetle, Xanthochroa waterhousei Harold, Collections and observations were made at various localities of Japan. 2. Adults of the present species is distinguished from those of allied species mainly by the structure of the apical part of abdomen. Larvae are characterized by possessing asperated ambullatory ampullae on the dorsum of three thoracic and first two abdominal segments as well as on the venter of 3rd and 4th abdominal segments, though in the first instar they are inconspicuous. Eyes of the last instar larvae absent, but 2 pairs of ocelli are discernible in the first instar. Eggs are subcylindrical, tapering towards both rounded tips, somewhat curved in whole shape, milky white in colour and 1.3 to 1.4mm in length. 3. The seasonal occurence of the adults varied by the localities, but was confined to early summer as the principle. In warmer parts of Japan such as in Kyushu, they could be collected from April to June; in Tokyo and in Kobe from May to July; in the mountains of Honshu as well as in Hokkaido where the climate is colder, they were found to be active until September. In other words, the seasonal distributions of the adult beetle and occurence of the dermatitis seem to be much influenced by the local climate, i. e. they appear earlier in season as climate gets warmer. 4. Diurnal activities of the adult beetle in nature was investigated. In the daytime, they usually stay still beneath leaves of trees. They become active towards evening and often fly around chestnut flowers in swarms. Through field observations, feeding experiments and dissections of the digestive organs, they were found to feed mainly on pollens of various kinds of flowers. 5. The results of light trap collections made repeatedly at Narimasu, Tokyo, showed that activities of the beetle were confined mainly in the first few hours of the darkening or of the premidnight type. 6. Secretions of the poisonous or dermatitiscausing fluid of the adult beetle (determined by the author and Watanabe as cantharidine) take place by compression on any part of the body. The fluid may be secreted from sublateral parts of the anterior and posterior margin of pronotum, longitudinal costae of elytra or the tip of each tarsus. 7. During copulation, a male stays on the back of a female in a parallel position. However, some of the females were often found to ride on other females and protrude their ovipositor, acting as if they were males in mating positions. 8. Females in cage insert their long ovipositor into narrow crevices and deposit eggs in a mass. Eggs are covered with a glutinous substance and are abhesive to each other. The numbers of eggs in a cluster varied from 56 to 221 in five times of observations. The incubation period was 7 to 14 days under the room temperature of 13.9℃ to 31.6℃. 9. Larvae in nature were found to burrow into rotten timbers of Sugi-tree (Japanese ceder) making holes just above or beneath the soil surface. In a laboratory breeding experiment, first instar larvae kept with the rotten timber emerged in May of the following year. The beetle seems to pass one generation in a year. 10. In the daytime collections in nature, the sex ratio of male to female was 43 to 57. In the light trap collections, males were much fewer than females only 2% of the total. Attractiveness towards the light source seem to be much stronger in the female.