Contents - LAC Biosafety

interacting factors are involved in determining the population size of a pest
and it is often difficult to identify which factor is responsible for precipitating
large-scale build up. Preventive measures are possible in some cases where
the causes of population build up are known. These measures usually consist of
silvicultural interventions aimed at tree health improvement in order to ‘tune
up’ the tree’s innate defence mechanisms. They are effective where pest build-up
is caused by poor tree health. Thus, as discussed in Chapter 10, preventing injury
to trees by lopping can prevent infestation by the teak trunk borer Alcterogystia
cadambae and prompt removal of overmature trees and regular thinning of
stands of Shorea robusta, as well as trapping and killing of moderately high
populations of adult beetles, can prevent outbreak of the sal borer Hoplocerambyx
spinicornis. Similarly, improvement of tree health and removal of dead and
unhealthy trees in a pine stand can prevent pine bark beetle outbreak. Prompt
removal of tree-felling refuse from a plantation site can prevent the build-up of
pests like bark beetles which infest and breed on freshly felled trees and
eventually attack healthy standing trees. In the case of teak defoliator outbreaks,
as discussed in Chapter 10, destroying the early epicentre populations during
the pre-monsoon period can prevent at least part of the subsequent large-scale
outbreaks. Silvicultural practices such as retention of plant species that support
alternative hosts of pest insects, as discussed under teak in Chapter 10, or
raising mixed-species plantations, as discussed in Chapter 8, can also reduce
pest build-up by enhancing natural enemy action. In the case of pests introduced
from other countries, quarantine measures, where potential pests are
intercepted at the ports of entry of commodities such as wood or planting
material, is also a preventive measure.
Use of pest-resistant trees can also be considered a preventive measure.
Resistance refers to the genetic capability of trees to prevent, restrict or
withstand pest infestation. There are not many instances of trees showing useful
resistance to pests. When present, tree resistance to insects is usually polygenic.
It may also be based on physical factors such as resin system characteristics.
Conventional breeding for resistance is constrained by the long reproductive
cycle of trees.
For pests of stored timber, preventive measures include immersing the logs in
water and debarking newly felled logs to prevent some groups of borers from
laying eggs beneath the bark.
9.3.2 Remedial measures
9.3 Overview of pest management options 157
Remedial measures aim to reduce the pest population level by killing
the insects by one means or other. A large variety of remedial measures has been
developed and tried against insects.