Pyriproxyfen bait for control of plague vector fleas (Siphonaptera:Ceratophyllidae) on rock squirrels (Rodentia:Sciuridae)

Abstract

Research was conducted in Albuquerque, Bernalillo County, New Mexico, to investigate the efficacy of orally administered bait cubes containing pyriproxyfen for control of the plague vector flea, Oropsylla montana (Baker), on rock squirrels, Spermophilus variegatus (Erxleben). Pyriproxyfen, accumulated in the squirrel blood, was ingested by feeding adult fleas, and was absorbed in the developing eggs preventing maturation of oocytes or hatching of larvae. Initially bait cubes containing another growth regulator, lufenuron, were fed to rock squirrels in the field. Fleas were collected from trapped squirrels and maintained in the laboratory to determine percent egg mortality. However, techniques for bait studies in the field proved inadequate. Flea eggs became desiccated, and bait consumption by the squirrels was uncontrollable. Consequently, additional studies were conducted with wild-caught squirrels maintained in an environmentally controlled laboratory. Squirrels were housed in individual cages containing nest boxes and infested with fleas to provide a continuous source of eggs. The use of lufenuron was discontinued. Instead, caged squirrels were fed bait cubes containing concentrations of pyriproxyfen ranging from 60, 100 and 200 mg per kg of body weight to determine the dosage needed to prevent egg hatch. Flea eggs were collected from the squirrel cages weekly, and egg hatch was determined for fleas fed on each group of test squirrels and compared with that for fleas fed on an untreated control group of squirrels. Results showed that 100 and 200 mg/kg dosages of pyriproxyfen effectively inhibited egg hatch for nearly two months or more. At a dose of 60 mg/kg of body weight, egg hatch rose to 50% during the third month after treatment, whereas the higher dosages of 100 to 200 mg/kg continued to prevent egg hatch at rates greatly exceeding 50%. At 200 mg/kg, pyriproxyfen prevented hatching of over 90% of the eggs for ~11 weeks in at least one of three replicates and for ~9 weeks from averaged data.