Contents - LAC Biosafety

48 An overview of tropical forest insects
Although the feeding habits of the dominant taxonomic groups were indicated
in Section 2.2.1, insects can be grouped into feeding guilds across the taxonomic
groups. A group of species that all exploit the same class of resource in a similar
way is called a guild and guild membership cuts across taxonomic groupings.
This kind of grouping helps to focus attention on the ecological functions of
insects as discussed in the next chapter and also on the impact of insects on the
forest. Under each feeding type some examples are given, but the major pest
insects will be discussed elsewhere.
Leaf feeders
Leaf feeders constitute a large proportion of forest insects. Members
of the orders Lepidoptera, Coleoptera and Orthoptera are the common leaf
feeding insects. Leaf is consumed in a wide variety of ways by different insects.
The simplest is the wholesale consumption of leaf by groups such as caterpillars
and beetles, of which there are thousands of species, together feeding on almost
all species of trees. Defoliation by caterpillars often results in widespread
damage to forest plantations. Some caterpillars, such as the teak leaf
skeletonizer Eutectona machaeralis and the early instars of most caterpillars,
feed only on the green leaf tissue between the network of veins which results in
skeletonization of leaves. Some caterpillars tie the leaf together or roll the leaves
and feed from within. Bagworms or case moths feed on leaves, hiding themselves
within bags made of leaf or other plant material. Some lepidopteran caterpillars
and some fly maggots (Agromyzidae) mine into the leaf between the upper and
lower epidermal layers and feed on the green matter, creating mines, blisters or
blotches of various shapes.
Sap feeders
Sap feeders constitute a comparatively small proportion of species, but
some are of economic significance because of population outbreaks or because
they act as vectors of disease. Most sap feeders belong to the order Hemiptera
although some Diptera (fly maggots) and Thysanoptera (thrips) also feed by
sucking. They feed on succulent plant parts such as tender leaf, shoot, fruit,
flower or seed by sucking the sap or liquefied tissues. Cicada, leaf hoppers,
psyllids, mealy bugs, scale insects and aphids are examples. Extensive outbreaks
of the leucaena psyllid Heteropsylla cubana and the conifer aphids Cinara spp. and
Pineus spp. have occurred across continents. Some bugs, like the tingid Tingis
beesoni on Gmelina arborea saplings and the mirid Helopeltis spp. on eucalypt
seedlings and saplings, inject toxic saliva during feeding causing necrosis of
plant tissue and shoot dieback. Others like the sandal bug Rederator bimaculatus
transmit pathogens to host trees (Balasundaran et al., 1988). Yet others, like