Susceptibility to insect growth regulators and cuticle deposition of the cat flea (Siphonaptera: Pulicidae) as a function of age.

Abstract

Wandering larval, pharate pupal, pupal, and pharate adult stages of the cat flea, Ctenocephalides felis (Bouché), were identified by examination of cuticular cross sections via scanning electron microscopy. Visible morphological characteristics of each stage were identified and described. Various stages of the flea throughout metamorphosis were exposed to juvenile hormone mimics and insect developmental inhibitors. Wandering larvae treated with juvenile hormone mimics were unable to pupate, whereas treated pharate pupae ecdysed to the pupal stage but were unable to enclose. Pupae and pharate adults did not succumb to juvenile hormone mimic exposure, even at concentrations 3 orders of magnitude greater than those that killed 100% of the wandering larvae and the pharate pupae. Adult females were more susceptible to juvenile hormone mimics than males. Possible explanations for the variation in tolerance to juvenile hormone mimics of the differing stadia are discussed. None of the stages were susceptible to insect developmental inhibitor exposure. Analysis of catecholamines that are precursors of cuticle sclerotization and melanization were measured in the wandering larval through the pharate adult stages of the cat flea. N-acetyldopamine concentration was highest in the pupa stage when the flea had a hard, clear cuticle; N-beta-alanyldopamine concentration was highest during the production of the hard, dark cuticle of the pharate adult; and dopamine fluctuated throughout development but was highest in the pupal stage.