Implantable Systems for Delivery of Insect Growth Regulators to Livestock.II

During the past several years, our laboratories have been investigating the application of controlled-release technology to the control of arthropod pests of livestock.1 As a result we have developed methods whereby an active ingredient can be delivered at a controlled rate into the circulatory system of a host animal via implanted pellets or microcapsules to affect feeding parasitic insects or ticks. Our initial experiments involved the preparation and bioevaluation of injectable microcapsules of the systemic pesticide famphur (O-[p-(dimethylsulfamoyl)phenyl]O, O-dimethyl phosphorothioate) in biodegradable polymers.2 Subcutaneous injections of a suspension of these microcapsules into guinea pigs killed feeding ticks over an extended period by continuously releasing active ingredient into the host’s circulatory system. However, large injections were required because of the relatively low activity of famphur and the volume of sesame oil used to suspend the microcapsules. Thus, this treatment was impractical for cattle. We therefore sought to avoid these problems by developing controlled-release implants of systemic insect growth regulators (IGR’s).