The pre-dispersal insect fruit-predators of Dipterocarpaceae in Malaysian rain forest
This study examines fruit predation of species in the family Dipterocarpaceae. It was conducted in Pasoh Forest Reserve, a Lowland Dipterocarp Rain Forest in West Malaysia. The work concentrates upon the pre-dispersal weevil predators, whose larvae develop within dipterocarp fruit. After describing the pre-dispersal predators the host specificity of their larvae is examined. A comparison of host records determined in this study with records in the literature demonstrates statistically significant generic specialization by the larvae of some weevil species. The larvae of other species are also restricted to hosts within one genus, but sampling effort was insufficient to demonstrate generic specialization. The most abundant pre-dispersal weevil predator was Nanophyes shoreae. Aspects of the biology of this species are described. These include: the activity of the adult weevils during dipterocarp flowering events; the timing of oviposition; the length of the pre-imaginal development period; the survivorship of adult beetles kept under laboratory conditions. The period of pre-imaginal development varied between host species but was consistent between trees of one species. Quantitative analyses of Nanophyes shoreae's pre-imaginal mortality are also described. The primary mortality factors were abortion of fruit containing eggs and consumption of pupae and III instar larvae by vertebrates. Adaptations that may reduce losses to these primary mortality factors are considered. They include oviposition within those fruit that are least likely to abort and variability in the length of the pre-imaginal development period, causing synchronous development in larvae developing from eggs that were deposited on different dates. None of the dipterocarp fruit predators could be located during periods when dipterocarp fruit were not available. Analyses of their population recruitment during fruiting events and of the availability of fruiting trees (as determined by a phenological survey of Pasoh Forest Reserve) indicates that they are unlikely to have dispersed widely in search of fruiting dipterocarps. The existence of an alternative larval or adult host is discussed.