Rat-control procedures on the Pacific islands, with special reference to the efficiency of biological control agents. I : Appraisal of the monitor lizard, Vuranus indicus (Daudin), as a rat-control agent on Ifaluk, Western Caroline Islands’)

Two kinds of rats, i.e., roof rats, Rattus rattm (Linnaeus) and Polynesian rats, Rattus exulans (Peale) have become widespread among the islands of the Central and South Pacific. Coconuts are being subjected to extremely heavy rat damage. Not only is there ensueing economic loss, but rat-gnawed coconuts are intensively utilized as larval habitats by mosquitoes including vectors of Bancroftian filariasis and dengue. Effective integrated rat control procedures are therefore of pressing importance to the Pacific islands in general. Such procedures would call for the joint use, against an adequate background of ecological knowledge, of chemical and biological control measures. The latter might well involve the use of predators, and in this connexion it has been reported that Varanus indicus (Daudin), a large grey-green monitor lizard which has been introduced into certain Micronesian islands, is of local importance as a rat-control agent, To appraise whether this lizard merits consideration for introduction elsewhere in Micronesia and Polynesia for the purpose of decreasing rat damage to coconuts, the present study was thus undertaken on the atoll of Ifaluk (lat. 07” 15’ N, long. 144” 27’ E), Western Caroline Islands. While it was established that V. indicus certainly makes some contribution to rat control, it is concluded that the data reported herein do not favour further consideration of an experimental introduction of this predator in the South Pacific area. It is submitted that a better candidate for a field trial against coconut-gnawing rats in the South Pacific would be the Japanese weasel, Mustela sibiricu itatsi Temminck & Schlegel. This animal is thus discussed in some detail xvilh reference to its environmental requirements and the practicability of establishing it under tropical conditions