Studies on the Use of Radioisotopes for the Control of Red Palm Weevil, <i>Rhynchophorus ferruginues</i> F. by the Sterile Insect Technique

Preliminary radioecological investigations were carried out and a technique for labelling red palm weevil with radioisotopes emittingtfradiation was developed. The weevils were tagged by inserting pieces of radioactive Ir idium wire, 1 9 2 I r into the flight muscles. Wi th a flight carrousel it was shown that tagging in this manner did not affect the ability of weevils to fly. The distances upto which marked weevil could be located were estimated. At a distance of 18m, the activity was reduced to approximately 30-40 %. Thus it is possible to detect labelled weevils at a considerably long distance. The half thicknessess of fresh and dry coconut timber for radiation emitted by radioctive Iridium, 1 9 2 I r and for radioactive Iodine, 1 3 1 I were also determined. The range of detection of radiation traversing through a coconut trunk was larger for 1 3 1 I than for 1 9 2 I r . However 1 9 2 I r was chosen for the tagging because of its longer half-life and as Iridum wire could be cut into small pieces of the required length for labelling the weevils. I N T R O D U C T I O N Red palm weevil is a serious pest of coconut in Sr i Lanka. Harmful systemic insecti cides have to be used to treat the weevil infested palms. However as grubs of the weevil feed on the tissues inside the trunk or crown and are not visible from outside, early detec tion of infested palms is difficult. Hence the damage is often fatal. Kloft (1984) reported that the Sterile Insect Technique (S.I.T.) is highly specific to the target pest and its use for pest control would minimise environmental disturbances within balanced ecosystems. Very intensive studies on the biology and behaviour of the target insect is a prerequisite to the use of S.I.T. For these studies, a convenient method of marking of insects with radioisotopes would be very useful as radiolabelled insects could be located by using radiation detectors. Rahalkar et al (1971) reported the work carried out in labelling adults of this weevil With Cerium for detection by Neutron activation analysis. However, only* emitting sources allow detection at a distance and through obstructions (Kloft, 1977 & 1984).