Bactrothrips brevitubus Takahashi 1935

Bactrothrips brevitubus Takahashi (Figs 3, 10 & 89) Bactrothrips (Bactridothrips) brevitubus Takahashi, 1935: 61–63. This species was originally described from Amami Is., the Ryukyu Islands, Japan, and is rather widely distributed in the subtropics and warm temperate zone of China, Japan and Taiwan. In Japan, it is widely distributed in evergreen broad-leaved forests, but not in the Ogasawara Islands. It is recorded here from Vietnam for the first time. This species is very similar to B. malayanus sp. nov., from which it is not always easy to distinguish depending on the local populations. However, the relative length of antennal segment III and the male abdominal tubercles, and the shape of the female Bournier’s Apparatus are slightly different. It is also closely related to B. idolomorphus, but the form of the female Bournier’s Apparatus is significantly different (see below under B. idolomorphus). These three species have antennal segment III relatively long, the male tubercles on abdominal tergite VI curved inwards in medium to large sized individuals, the female Bournier’s Apparatus with tufted area well-developed (Figs 55, 78 & 89) and the male subgenital plate slender and tie-shaped (cf. Fig. 10). They are probably sister species and constitute a species-group, idolomorphus -group. Since B. brevitubus is widely distributed, it exhibits very complex intraspecific variation, and is not easy to define. It shows not only variations related to body size, but also to geographical area. The variation related to body size is common to all congeners, so we will not discuss it here. The specimens from Taiwan are usually not distinguishable from the specimens from Japan including the Ryukyu Islands, the type-locality, but sometimes the male abdominal tubercles are more yellowish.The specimens from Vietnam are slightly different from them, but there is not significant difference to divide the species. In particular, the female Bournier’s Apparatus is indistinguishable from the typical form of this species. The specimens from Central Vietnam (Quang Binh Prov.) have the postocellar setae short, almost as long as a diameter of a posterior ocellus. The specimens from South Vietnam (Lam Dong Prov.) are listed under the doubtful-specimens because they are the most morphologically unique population. They have the intermediate antennal segments with the club-head paler, the pedicel weakly tinged with pale brown and the postocellar setae somewhat longer, longer than a diameter of posterior ocellus. This population is very similar in appearance to B. malayanus sp. nov. and is not always easy to distinguish, but antennal segment III is slightly but definitely longer. The relative lengths of their antennal segment III are almost typical of brevitubus, 0.61–0.68 times as long as head in female (means±SD=0.63±0.01, n=32), 0.63–0.70 in male (means±SD=0.66±0.02, n=17). To determine the exact taxonomic status of this population, it is necessary to study more populations in the surrounding area. Specimens examined. Japan, numerous females and males from Honshu, Shikoku, Kyushu and the Ryukyu Islands (detailed data are omitted). Taiwan, numerous females and males (detailed data are omitted). C. Vietnam, 3 females and 1 male, Quang Binh Province, Bo Trach District, Son Trach, nr. Phong Nha, 14.viii.2007, SO. Doubtful-specimens. S. Vietnam. 32 females and 17 males, Lam Dong Province, Bao Loc, Dam Bri, on dead leaves, SO.