Contents - LAC Biosafety

102 Insect pests in plantations: general aspects
eucalypt insect fauna have been recorded in the temperate region. The
comparatively higher number of insects in the case of bamboos and Acacia
mearnsii is also due to inclusion of some insects from the temperate regions.
About half of the tree species examined had 40 or fewer number of associated
insect species and about a quarter had 10 or fewer. A smaller percentage of trees
had higher numbers of associated insects. Obviously the number of species of
insects associated with a plantation tree species will be influenced by several
factors – the chemical profile of the species, the extent and climatic diversity
of the geographical area covered, the period over which the species has been
cultivated on a large scale etc.
Although fairly large numbers of insects are associated with all tree species,
most of them are casual or minor pests. Only a few species have acquired major
pest status on any given tree species. While some of these are chronic pests
causing serious damage every year, others cause serious damage occasionally.
The number of serious pests listed in Table 5.2 is therefore based on subjective
judgement. Serious pests include defoliators, sap suckers and stem borers.
Leaf-feeding insects occur on all tree species, with serious pests occurring on
Ailanthus, Dalbergia sissoo, eucalypts, Falcataria moluccana, Gmelina arborea,
Neolamarckia cadamba and Tectona grandis. Sap-sucking insects are not major
pests except in Leucaena leucocephala, Milicia and pines. Among the trees not
included in the detailed case studies in Chapter 10, a sap-sucking bug, Rederator
bimaculatus (and possibly other bugs) is responsible for transmitting a serious
disease known as spike disease, caused by a mycoplasma-like organism in the
sandal tree, Santalum album. Stem borers are major pests of Dalbergia
cochinchinensis, Falcataria moluccana, pines and Shorea robusta. Detailed accounts
of these pest problems are given in Chapter 10.
In summary, most tree species raised in plantations are attacked by one or
more serious pests; freedom from pests is exceptional. This is in contrast to the
situation in natural tropical forests where serious pest attack is exceptional.
5.4.1 Impact of pests in older plantations
For some tree species, pests have a devastating impact in plantations,
much more serious than in the mixed species natural stands. The details are
covered in Chapter 10. In Asia, annual defoliation caused by the caterpillar
Hyblaea puera in teak plantations has ben shown to result in loss of 44% of the
wood volume increment. This pest is becoming increasingly important in exotic
plantations of teak in Latin America, but has not so far become serious in Africa.
Chronic defoliation caused by other insects on other trees must also be causing
serious economic loss, but the losses have not been quantified in most cases.
The sap-sucking leucaena psyllid has had a devastating impact on the cultivation