This article is contributed by Arthur Y.C. Chung of the Sabah Forestry Department
One of the many examples of remarkable diversity of live forms in Sabah’s forests is beetle. Scientifically known as Coleoptera, it is characterized by a pair of hardened forewings, called elytra, protecting the delicate membranous hind wings and the abdomen beneath it. The body and the elytra are usually heavily sclerotized, giving the beetle an armoured appearance, which also protect it from dehydration and ultraviolet radiation. Throughout the world, it has been estimated more than 400,000 species of beetles. This number has put beetles as the largest group of insects, representing a fifth of all living organisms and a fourth of all animals. Their diversity is not only seen in number, but also in size, colour, pattern, form, as well as strategies of behaviour, defense, reproduction, and adaptation which has been appreciated since the time of Pharaohs. This makes them an important group to study if we are to understand the assemblage structure and diversity of the insect fauna in various tropical habitats.
Importance of beetles in the tropical ecosystem
Due to their high diversity, beetles can be used as indicators of environmental change. They are found in numbers in most vegetation types and can be easily sampled using various techniques. Beetles are widely used in studies on diversity and ecology. Documentation of diverse and ecologically important insect groups, such as assemblages of beetles, can provide qualitative and quantitative measures of biodiversity that provide a basis for decision making in relation to conservation.
Many beetles attack living trees and, thus, reduce the commercial value of their timber. They also sometimes cause the death of the trees, either directly or by transmitting pathogens. Some scarab beetles attack and cause severe damage to oil palm and rattans. The gold dust weevil, Hypomeces squamosus, is one of the commonest defoliators that attacks many tree species, including dipterocarps and fast-growing exotic tree species. Many long-horned beetles are stem-borers: their larvae can severely damage trees, resulting in devaluation of timber and, sometimes, tree mortality, such as the ‘lubang pusing’ or Cyriopalus wallacei, on dipterocarps in Sabah. Ambrosia beetles (Scolytinae and Platypodinae) also cause damage to many species of forest trees and rattans.
Some beetles are beneficial to humans. The discovery of a weevil pollinator had a dramatic effect on production in Malaysian oil palm plantations. The weevil, Elaeidobius kamerunicus, was introduced into Malaysia in 1981 to replace the practice of assisted pollination. It was also reported that beetles of the families Chrysomelidae and other Curculionidae contributed to the pollination of timber trees. In addition, dung beetles (Scarabaeidae) are important decomposers and nutrient recyclers in the rain forest. As their name suggest, they feed on dung. By burying and consuming dung, they improve nutrient cycling and soil structure.
Beetles also contribute towards nature tourism, especially fireflies. Despite their name, they belong to the beetle family Lampyridae. In Malay, they are called ‘api-api’, ‘kunang-kunang’ or ‘kelip-kelip’. They have fascinated man for centuries because of their ability to produce a fascinating display of light. This light is used as a means of sexual communication between the males and females of a particular species. In Sabah, this amazing light display from the fireflies can be seen at the Klias Peninsula, Sg. Paitan, Abai in Kinabatangan, Labuk Bay, and various other riverine and mangrove areas.
Beetles are important source of food for other animals in the forest. Many predatory mammals feed on adult beetles while many birds often prey on the larval form of beetles. Even among the Kadazandusuns in Sabah, some of the larvae, pupae and adult beetles are procured for food. The commonest is the sago grub, Rhynchophorus vulneratus (Curculionidae). The grubs are mainly consumed by the local people in western Sabah where the sago palms are abundant. These creamy yellow larvae are collected from the felled sago trunk, left decaying for about 2-3 months. They may also breed in fallen coconut and arenga palms. The grubs are considered a delicacy in the village cuisine although they may not be so common nowadays.
Considering the diversity and some of their significance highlighted here, there is so much to explore on this insect group, and we are far from discovering the end of beetle diversity. Thus, the study of beetles is fundamentally essential to humans, in biodiversity, forestry, agriculture and contributes towards the socio-economic development of Sabah.