Yutaka Johki

A new type of microhabitat, the interface between the log and the ground, observed in the passalid beetle of borneoTaeniocerus bicanthatus (Coleoptera: Passalidae)

The Passalidae are a pan-tropical family of Coleoptera, all species of which apparently live in rotting wood in colonies composed of both adults and larvae, though a few species have been known to live in other microhabitats (Schuster 1978; Reyes-Castillo & Halffter 1983). Since first being reported by Ohaus (1900), the subsocial behaviour of passalid beetles has often been cited in the entomological literature (Wheeler 1923; Gray 1946; Wilson 1971; Matthews & Matthews 1978; Eickwort 1981; Halffter 1982; Reyes-Castillo & Halffter 1983). However, all these studies were restricted to New World species. Although Gravely (1914) suggested that, in Oriental species also, adults of nearly all species lived in decaying wood in pairs with their young, relatively little is known about the life of Oriental passalid beetles. We had an opportunity to collect some passalid beetles in Sabah, North Borneo in August, 1985 and found the Bornean species, Taeniocerus bicanthatus, living on the ground under the log in colonies, not tunneling into the log. We report briefly its unique microhabitat, body shape and colony composition. Thirteen colonies were collected in the plantation at Brumas. They occurred in bisexual pairs or as pairs with their young, excepting one colony composed of one female adult and 2 larvae (Table 1), and were living in the interface between the log and the ground. In addition, 2 single females were collected in the same microhabitat, but it was not observed that the larvae occurred alone without adults. It has been reported by some authors (ReyesCastillo & Halffter 1983; Johki & Kon 1987) that, in passalid beetles, flatter species tend to be found under the bark, more convex species deeper in the log, while a few species occur in other microhabitats, e.g., among decaying vegetable refuse (Gravely 1914), under epiphytic bromeliads, in the nests of leaf-cutter ants, in caves with a large colony of oilbirds (Schuster 1978) and among the rhizomes of epiphytic ferns (Johki & Kon 1986). However, the microhabitat of the interface between the log and the

Group feeding in larvae of the albizia borer,Xystrocera festiva (Coleoptera: Cerambycidae)

Larval aggregation in insects has been widely studied by ecologists and ethologists, and several authors have also discussed its adaptive significance (Fujisaki 1972; Morimoto 1972, 1979; Tsubaki 1981; Tsubaki & Shiotsu 1982). In the longicorn beetles (Cerambycidae), however, there is no report on larval aggregation. In all species of Cerambycidae in which the immature stages are known, the larvae do not aggregate and are known to tunnel solitarily in the plant (Duffy 1968; Kojima & Hayashi 1969). When 2 larvae are digging tunnels and encounter, severe combat and cannibalism occur between the 2 insects (Yukawa 1977). Powell (1982) reported that in the Eucalyptus borer, Phoracantha sernipunctata, the major mortality factor in the larval stage was intraspecific competition due to severe overcrowding in the logs. During the course of a biological survey in Sabah, Malaysia in 1981, we found the larvae of the Albizia borer, Xystrocera festiva (Coleoptera: Cerambycidae), aggregating in the same gallery under the bark of a living Albizia tree, Paraserianthes falcataria (Hidaka et al. 1983). Subsequently, other Japanese investigators studying the forest pests in Sabah have reported on this behavior (Abe 1983; Mori 1986). In this paper the curious behavior of X. festiva larvae is reintroduced and reemphasized as the first and only example of larval aggregation in longicorn beetles. The adaptive significance of X. festiva will also be discussed in comparison to Xystrocera globosa, which is a congeneric but solitary species. Observations were made at Luasong and Brumas, south-eastern sector of Sabah, in July, 1981 and in August, 1985. The rapid-growing leguminaceous trees, Paraserianthes falcataria, have been planted in large scale by Sabah Softwoods Co. Ltd., and such plantations are subject to attacks by X. festiva (Fig. 1). Combining the results of our observations with the descriptions of X. festiva by Duffy (1968) and Franssen (1937), its life history can be summarized as follows. This species attacks healthy Albizia trees, but the eggs are laid into man-made wounds and dead stumps of fallen branches. A batch of 2 0 4 0 eggs is laid in one place. After hatching, larvae aggregate and feed on the sapwood just underneath the bark (Fig. 2). They dig a wide tunnel downwards along the tree trunk. This aggregative behavior is maintained throughout the larval stage until they make pupal chambers. Pupal chambers are made individually by digging an upward tunnel into the xylem. The entrance of the chamber is closed with a thin lid of calcium carbonate and the pupa is situated head down. Adults creep out easily from the tree by breaking the cover of the chamber and emerge through the bark which has been made ragged by the larval infestation. Feeding, migration and mating behaviors in adults are still unknown, although copulation appears to occur on the healthy trunk of Albizia trees. In 1981 and 1985, we investigated 6 groups of feeding X. festiva larvae. Larvae were preserved in 80 % ethanol and the body length and the head capsule width were measured. Table 1 shows the number of larvae, mean body length and mean head capsule width for each feeding