Contents - LAC Biosafety

90 Insect pests in natural forests
Hemiptera
Phytolyma spp. (Psyllidae) on Milicia spp. in Africa
The psyllids Phytolyma spp. attack Milicia (syn. Chlorophora) spp. in Africa.
P. lata on M. regia is the most damaging (Wagner et al., 1991). The insect lays eggs
on buds, shoots or leaves of the host plant. The newly hatched nymph bores into
the plant tissues causing the formation of a gall which completely covers the
nymph. Galls may develop on bud, shoot or leaf and may occur singly or in
clumps. Several galls will often coalesce and become a bunched mass affecting
the growth of the shoot, particularly of young plants. When the infestation is
heavy, the shoots and leaves become a putrefying mass, the stem dies back and
the seedling may eventually die. While damage by Phytolyma has been noticed in
natural forests, the injury is more severe in nurseries and young plantations
below one year old; 100% failures have sometimes been reported in nurseries
and plantations in Ghana (Wagner et al., 1991). A pest profile of Phytolyma spp. is
given under Milicia species in Chapter 10.
Udonga montana (Pentatomidae) on bamboos in India
The pentatomid bug, Udonga montana feeds on the developing seeds
of bamboos. Very heavy build up of this bug has occurred periodically in bamboo
forests in India and Myanmar, coincident with gregarious flowering of bamboos.
Huge swarms of the insect assemble on all sorts of trees and vegetation during
these periods. Characteristics of these outbreaks are described more fully under
bamboos in Chapter 10.
Hymenoptera
Shizocera sp. (Argidae) on Manglietia conifera in Vietnam
Larvae of the sawfly Shizocera sp. feed on the leaves of the Mo tree,
Manglietia conifera (Magnolaceae) in mixed natural forests in Vietnam. Outbreaks
have occurred often in pure stands of the tree in the northern temperate region of
Vietnam with an average temperature of 21–24 °C (Tin, 1990). The insect passes
through one or two generations per year depending on the temperature
conditions. Additional details are given in Chapter 10.
4.3 Discussion and conclusion
The empirical evidence shows that contrary to conventional wisdom
tropical forests are not free of pest outbreaks. All gradations of insect damage,
from minor feeding with no significant impact, to large-scale outbreaks
resulting in massive tree mortality have been observed.