THE RHINOCEROS BEETLE | Description, Types, Infestations, & Facts




Beetles are insects in which the first pair of wings has become modified to form wing cases or elyrra. These elytra have a thick cuticle, show no veins and meet in a straight line down the back of the insect, and in most species cover the entire dorsal surface of the abdomem. The hindwings, when not in use, are folded away under the elytra. During flight, the elytra are held out from the body but are motionless while the vibrating hindwings provide the propulsive force.


 There are over 40 species of beetles in the genus oryctes and 25 of them are known to attack palm trees. The life cycle outlined here is a general one, more or less applicable to several species, e.g. Oryctes monoceros or O. owariensis.


The mature female lays about 100 eggs in soft, dead Wood, e.g. rotten palm trunks or stumps, sawdust pits or the debris at the bases of dead leaf stalks of living palms.


The eggs, which are about 3 to 4 mm long, hatch within two weeks to small white larvae with brown heads. The larvae burrow in the dead wood, cutting it up with their powerful mandibles and eating it. The larva goes through three instars, moulting its cuticle between each instar and growing to as much as 100 mm long in ten to fifteen weeks.


If the larva has been living in wood, it makes an oval cell and blocks the entrance with sawdust and faeces. In softer or fibrous material, a kind of cocoon may be constructed from the fibres or sawdust by glueing it with semi liquid excretory matter. Pupation may also occur in the soil.


In about three weeks, the imago emerges from the pupa and eats its way out of the pupal cell or cocoon. In about 24 hours its cuticle, which was at first white and soft, becomes dark and hard and the adult beetle flies of and finds a mate.


The larva normally burrows in dead wood but it may invade the palm trunk, particularly if the tree is already diseased and unhealthy, and so cause damage to the living tree. Most damage is caused, however, by the imago which flies to oil, date or coconut palms. The adult insect bores into the crown of the tree, chews at the bases of the leaves, and then sucks up the juices released from them. Sometimes the adult may cut off the leaves entirely and frequent attacks by numerous beetles may completely kill the tree.


The adults have very thick cuticles and bore so deeply into the palm crowns that applications of insecticide do them little harm. The best method of control is to destroy the breeding grounds by cutting down and removing dead and diseased trunks, coating stumps in creosote and clearing all vegetable litter from the bases of trees.


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