Japanese Shot-hole Borer-Dinoderus japonicus Lesne

Ghoon Borer-Dinoderus minutus Fabricius

Heterobostrachus aepualis Waterhouse

There are about 16 bostrychid species attacking post-harvest bamboos in Asia. The most important species are all from the genus Dinoderus and include D. japonicus Lesne, Dinoderus minutus Fab., D. ocellaris Stephens and D. brevis Horn. They are responsible for over 90% of insect damages on harvested culms and finished bamboo products. These species have very similar life histories and damaging habits. Both adults and larvae feed inside felled culms, but the latter causes the major damage. Adults burrow through wounds or cut ends into the culm and make horizontal tunnels around culms, where eggs are deposited. Larvae bore longitudinally in the culm. Heavy infestation results in numerous criss-crossing tunnels which are tightly filled with excreta. The fully developed larvae make chambers in which they pupate. Adults emerge out through the external rind just above their pupal chambers.

  Japanese Shot-hole Borer - Dinoderus japonicus Lesne

Widespread in almost all bamboo-growing countries.

The adult beetle is 3.5-5 mm long, dark brown in colour and covered with dense punctums and brown hair. The borer mostly has an annual life cycle and overwinters as adults. Individuals vary significantly in development rate. A small portion of adults emerge in July and produce the second but incomplete generation which overwinters as larvae. Adults emerging after July remain in the tunnel until the following April. The adult stage lasts from July to the following June, and larvae feed in culms from May to August. Adults have obvious preference in selection of egg-laying sites. Phyllostachys viridis is most favoured and P. pubescens and Pleioblastus amarus are free from attack when culms of the three species are stacked together. However, if P. viridis is not available, others are infested. They prefer newly-felled culms and basal, which has the highest market value (Liu Jinying 1956; Chang Lefeng et al. 1979).

  Ghoon Borer - Dinoderus minutus Fabricius

Bambusa bambos, B. polymorpha, B. textilis, B. vulgaris, Dendrocalamus giganteus, D. hamiltonii, D. strictus, Phyllostachys pervariabilis, P. pubescens.

This beetle is probably the most destructive and widespread insect pest on felled culms and finished bamboo products. The adult is about 3 mm long, reddish or dark brown in colour and covered with dense punctums and hair which are more obvious on the rear end of the wings. There are three generations in China and 3-4 generations in South Asian countries per year, but the generations are heavily overlapped. Adults and larvae can be found at any given time of the year and overwintering is not distinct, although they are less active in cold winter. Eggs, laid individually in tunnels mined by adults, hatch in 5-8 days. Larvae bore longitudinally in the culm and take about 40 days to develop. Pupation occurs in cocoons made at the terminal end of larval tunnels. The newly developed adult beetles may fly away or may explore other parts of the same bamboo.

DAMAGE CAUSED

Adult beetles burrow into felled culms through wounds, cracks and cut ends, and make horizontal tunnels along the fibrovascular tissues of the culm; larvae make longitudinal tunnels. The beetle shows strong preference to newly-felled culms of some species, while others ----such as Pseudosasa amabilis and Pleioblastus species ----are hardly ever attacked. Culms from level sites are more susceptible to attack than those felled from sloping sites. A large population of the borer will leave numerous tunnels in the culm, making it useless.

CONTROL

A chequered beetle (Coleoptera: Cleiridae) preys on the borer in the boring tunnels (Liu Yun and Xu FM 1982; Tan Zhongyi 1984; Wu Jianfen Huang Zenghe 1986). D. minutus, and D. brevis and D. ocellaris (two other major borers reported in South Asia as major pests of bamboos in storage), are parasitized by Spathius bisignatus Walkn. and S. vulnificus Walkn. (Hymenoptera: Braconidae). The larvae, pupae and beetles are preyed upon also by Tillus notatus Kulg. and T. succinatus Spin (Coleoptera: Cucujidae) (Beeson 1941; Chatterjee and Mishra 1974). These natural enemies cannot be relied upon as an effective control method, although they can cause high mortality of the borers.

Some preventive and preservative measures have been developed against these borers. The timing and age of felling are very important. Culms will have less soluble carbohydrates, proteins and moisture as they get older, and they are less active physiologically in winter season and thus more resistant to the timber borers. Hence, harvesting only culms over 3-4 years old and felling at winter season are particularly recommended.

After felling, treating culms physically or chemically can significantly improve their resistance to borers as well as to fungus. The traditional and most simple method is to immerse felled culms in water. This method may be effective only in preventing damages from bostrychid beetles. It is also suitable only for those bamboos with a low starch content (Sulthoni 1990), takes a long time, and culms treated in this way tend to blacken (Xu Tiansen 1983). Heating of culms by fire or boiling water, or putting them under direct sunlight in hot summer can kill borers in the culms. Some advanced microwave and infrared techniques have been developed recently for killing the borers in bamboo culms (Yao Kang et al. 1986).

BIOLOGY

This is a polyphagous species and a common pest of packing cases, plywood chests and other wood-based industrial products. It is a minor pest of dry bamboos. The adult beetle is black, 6-15 mm long, cylindrical and with a rough hooded prothorax, usually with curved hooks at the distal ends of elytra. Female adult lays eggs singly on rough surfaces of dry bamboos. The larvae, after hatching, bore into the soft portion and gradually make a wide tunnel. The tunnels are tightly packed with fine wood dust and the host bamboo is soon reduced to powder. The life cycle of the beetle is annual.