In a study of the incidence of damage to coconut palms in Madagascar and the Comores Archipelage caused by species of Oryctes (Scarabaeidae) it was found that attack is heaviest in localities where there are abundant breeding sites for the beetle, and that tall palms are more often attacked than short ones. The most important larval breeding sites are dead standing coconut palms and decaving coconut trunks and stumps. Larvae also breed in decaying satra trunks (Medemia sp.), wood of Albizia in coffee plantations, decaying Raphia trunks, and occasionally in rubbish heaps and manure, but are only rarely encountered in decaying wood in forests. Coconut palms are important feeding sites for O. gigas, O. blucheaui and O. simiar. O. pyrrhus attacks coconut seedlings and young oil palms. Forest palms are occasionally attacked. O. ranavaloattacks bamboo on the east coast. Banana plants are occasionally attacked by O. simiar.

Scoliid parasites of the larvae of Oryctes are widely distributed but not commonly found. Gregarines in larvae are also widespread but of rare occurrence. Oxyurid nematodes were often found in the fermantation chamber at the gut of Oryctes and Cetonid larvae. The fungus Cordyceps sp. was found at only one locality where it was attacking 56 per cent. of the larvae of Oryctes. Examples of infection by the fungus Metarrhizium were rarely encountered. Namatodes often occurred in the aedeagus of adult males of O. gigas and in the bursa copulatrix and colleterial glands of adult females, as well as under the elytra. They were less common in the other species of Oryctes examined. Mermithid nematodes were found in adults of Oryctes on rare occasions. No insect parasites of the adult stage of Oryctes were found. Elaterid larvae, possibly predacious on those of Oryctes were occasionally found but did not appear to be of much importance.

It is concluded that the major factor limiting Oryctes populations in Madagascar and the Comores is the number of suitable breeding sites.