Under ordinary conditions a healthy Hevea tree is practically immune from the attacks of boring insects, owing to the presence of latex, which is found an effectual check to the progress of these pests. If, on the other hand, an area of bark is killed by wounding or by the attacks of fungi, the latex soon dries up. Boring beetles and other insects then readily obtain access, and contribute materially to the damage done to the tree. The insect attacks are however purely secondary, and fiheir prevention is essentially bound up with that of the original cause of damage, which is usually a fungus disease
There is however one insect, prevalent in the Malay Peninsula, which is able to cause considerable damage to living Hevea trees without the assistance of fungi. This is a species of white ant known as Termes Gestroi, which is apparently able to effect an entry through the roots of entirely healthy trees. The insects then rapidly proceed to eat out the interior of the wood. Tertnes Gestroi is a pest which requires to be seriously taken in hand at its very first appearance. By digging a shallow trench round an affected tree it is often possible to locate the position of the termites' nest, because the insects quickly build covered ways across the bottom of the trench in order to obtain access to their food supply, and by following these up the direction of the nest can be determined. The best means of exterminating the white ants is by pumping into their nests the fumes of sulphur and white arsenic, generated by heating these substances over burning charcoal in a special apparatus. The channels excavated in the affected tree may be similarly fumigated, but if the damage has proceeded far it is simpler and more effective to cut down the whole tree and burn it.
In its early stages of growth Hevea is susceptible to the attacks of a somewhat larger variety of insect pests. Young plants in nurseries, and those which have recently been planted out in clearings, are subject to damage from cockchafer grubs, cutworms and similar subterranean creatures which gnaw the roots. These may be got rid of to some extent, at least in nurseries, by treating the soil with kainit or with " vapourite," a preparation sold for the purpose.
One animal against which the presence of latex is no protection is a slug Mariaella Dussumieri which actually drinks the latex, and appears to thrive upon a beverage which most animals would find decidedly indigestible. These slugs may do considerable damage by eating off the buds and young leaves. They may be prevented from climbing the trees by painting a band of tar round the trunk. Another method is to steep sawdust in a ten per cent, solution of carbolic acid, and sprinkle it round the bases of the trees. Such measures, in addition to protecting the trees for the time being, soon lead to a diminution in the numbers of the pest by cutting off the latter from its principal supply of food.