Contents - LAC Biosafety

50 An overview of tropical forest insects
Dead-wood feeders
The insect fauna that thrives on dead wood in the tropical forest is very
rich and includes members of the coleopteran family Cerambycidae, which feed
on freshly dead wood, as well as smaller beetles of several families and termites
which feed on drier wood. In addition, there are insects that feed on decaying
wood on the forest floor. The dead-wood feeders will be discussed in detail in
Chapter 3.
Insects that feed on litter, fungi, algae, root, animal dung, and soil
This heterogenous group of insects constitute a large proportion of
the total insect fauna, with members drawn from the orders Coleoptera,
Collembola, Hemiptera, Orthoptera and Isoptera. They are involved in the
breaking down of dead plant biomass. Litter-feeding insects are discussed in
detail in Chapter 3. A study of British insect fauna showed that more than half
of the insect species were carnivorous or saprophagous (Strong et al., 1984).
This must be true of tropical insects as well. A variety of coleopteran larvae feed
on roots, animal dung and soil, as do many species of termites. Many insects
feed on fungi associated with decaying matter. Even among the canopy
insects, many species are scavengers and fungivores (Table 2.2). Trees usually
have a large guild of Psocoptera feeding on fungal spores, algal cells and
lichen present as micro-epiphytes on the bark and leaf surface (Broadhead
and Wolda, 1985).
Predators and parasitoids
Predators and parasitoids constitute a large group of insects. They
feed mostly on other insects. Predators belong to several orders – Hemiptera,
Dictyoptera, Odonata, Dermaptera, Neuroptera, Coleoptera, Diptera and
Hymenoptera. Most parasitoids belong to Hymenoptera as discussed in
Section 2.2.1 and some to Diptera (family Tachinidae).
2.3 The concept of pests
The above discussion has shown that there is a great diversity of forest
insects adapted morphologically, physiologically and behaviourally to feed
on almost all forest vegetation and organic matter derived from it. By feeding on
a variety of substances, they perform some ecological functions which
are discussed in Chapter 3. As will be shown, the activities of some groups of
insects such as decomposers and pollinators are beneficial to trees, but insects
feeding on living trees have a negative impact on the growth and survival of
individual trees. This impact becomes all the more serious in plantations.