The System Under Study
Individual dipterocarp can trees can produce millions of fruit each, but these are often destroyed by insects, particularly beetles and moths.
This destruction can have a major effect on how many seeds germinate, and could be the reason why many dipterocarp species fruit at the same time, in order to overwhelm predators.
Identifying the insects, and their associations with host trees, will help in understanding and protecting this forest ecosystem.
Dipterocarp fruit are winged, and spin as they fall, drifting away from the parent tree. Dipterocarps can be extraordinarily prolific in seeding, with some mature trees producing up to 20 million flowers at a time.
In much of South-East Asia, the majority of dipterocarp trees flower and fruit together at intervals of five to six years, thought to be triggered by the El Niño-Southern Ocean Oscillations.
This synchronous or ‘mast’ fruiting, overwhelms animals that feed on the fruit, enabling the surviving seeds to germinate. This strategy is known as ‘predator satiation’.
Even within the masting areas some trees fruit every year. For these species insect predators are particularly damaging.
Dipterocarp fruit is eaten by a variety of animals, but insects tend to prefer the fruit of specific tree species.
All of the known insect predators of dipterocarp fruit, up to germination, are beetles and moths. A range of flies, termites and other insects have been found in decaying fruit, but are not recorded in the dipterocarp insect seed-predator host database.
The beetles found feeding in dipterocarp fruit are mainly weevils (Curculionoidea). In all cases it is the larva that feeds on the fruit, but when the eggs are laid is dependent on the species of weevil.
- Members of the genera Alcidodes, Nanophyes, Diplophyes and Damnux lay eggs in the young fruit. Adults may emerge from the fruit before it dispersed (Nanophyes, Damnux, Diplophyes), or after dispersal (Alcidodes).
- Niphades in Borneo lays its eggs either just before fruitfall or just after it, and the larvae develop in the base of the fruit feeding on the cotyledons, even while the seedling is developing.
- Coccotrypes, Sitophilus and possibly Trochorhopalus, are post-dispersal seed predators, laying in the fruit once it has fallen.