A review of dipterocarps - Center for International Forestry Research

Pests and Diseases of
Dipterocarpaceae
C. Elouard
Introduction
There has been relatively little research on the pests
and diseases of dipterocarps. Most investigations have
been directed to forest products commensurate with
their economic value. Now that dipterocarps are being
established by enrichment planting in forests or in
extensive plantations, more attention will have to be
directed to the pests and disease problems of living
trees.
Pests and diseases on dipterocarps affect seeds,
seedlings, saplings, trees and their products. A large
proportion of earlier studies catalogued dipterocarps’
pests and diseases. Little is known about their ecology,
natural enemies, management and control. The only
well-studied species is Shorea robusta, an important
timber species in central and northern India and grown
in plantations. Pests have been investigated on forest
trees only when mortality resulted in economic loss,
as for Shorea robusta in India. There has been
considerable work on pests of Indian dipterocarps
(Stebbing 1914, Beeson 1941, Bagchee 1953, 1954,
Bagchee and Singh 1954, Bhasin and Roonwal 1954,
Bakshi 1959, Mathur and Balwant Singh 1959, 1960a,
b, 1961a, b, Mohanan and Sharma 1991). Dipterocarp
diseases are mainly recorded as fungal diseases. The
only record of bacterial disease is Agrobacterium
tumefaciens, causing leaf gall formation on saplings
(Ardikosoema 1954, Torquebiau 1984, Smits et al.
1991). An alga, Cephaleuros virescens, is reported
causing leaf disease (Mittal and Sharma 1980, Elouard
1991).
The establishment of forest plantations and the
enrichment planting of logged-over forests with local
species such as dipterocarps requires collection of
fruits, seed storage and raising of seedlings in nurseries.
Chapter 7
Thousands of seedlings growing in a confined place can
lead to the development and proliferation of nonspecific
and even specific pathogens and pests. A timber
trend study in India (Anon. in Bakshi et al. 1967) shows
that combined loss in forest wealth due to causes like
fire, decay, insects and windfall is 13 per cent. This
emphasises the need for proper integrated pest and
disease management to protect investments.
Pests and pathogens are present in forest
ecosystems at all stages and take an active part in their
ecological balance and dynamics. Though pathogen and
pest damage is kept controlled at non-epidemic levels
in natural forests (Augspurger 1990), logging activities
change the natural balance of the forest ecosystems,
and can favour proliferation of pests and pathogens.
Moreover, enrichment planting and forest plantations
can be a dramatic source of pest and disease
propagation, particularly on monospecific plantations
such as the case of the leaf blight (Microcydus ulei) of
rubber in South America. The major epidemics recorded
on dipterocarps are caused by insects on Shorea
robusta, e.g. Hoplocerambyx spinicornis
(Cerambycidae), an important heartwood borer in India
and Pakistan, and the mealybug Drosicha stebbingi
(Coccidae) which have caused considerable damage
(Beeson 1941).
The main constraints to research on dipterocarp
pests and diseases are shortage of trained staff, lack of
cooperation among scientists and institutions in Asia,
inadequate funding and infrastructure facilities, high
cost of pest and disease identification, lack of
information on the economic effects of pests in
plantation forestry, and need for more contacts between
researchers, foresters and staff of timber companies.