Morphogenetic and Histopathological Effects Induced by the Insect Growth Regulator Cyromazine in Musca Domestica (Diptera: Muscidae)

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Abstract
Cyromazine [Larvadex (N-cyclopropyl-l,3,5-triazine-2,4,6-triamine)], a triazine insect growth regulator (IGR), induced a range of delayed morphogenetic aberrations in treated 3rd-instar larvae and subsequent developmental stages of house flies. The most common effect at higher concentrations (1 and 1.5 ppm) in rearing medium was the formation of larviform puparia. These aberrant puparia were rodlike, C-shaped, or elongate and generally twice as long as normal puparia. At a concentration of 0.5 ppm, failure of adults to eclose properly was the most prevalent effect. The extent of this abnormality varied from no eclosion to complete eclosion with slight attachment of the adult legs to the puparium. Some other morphogenetic effects were also noted and are discussed. At the highest concentration (1.5 ppm), most of the morphogenetic aberrations were observed in the pupal stage, while at 0.5 ppm most of the morphogenetic aberrations occurred in the adult stage. Treated 3rd-instar larvae of house flies were examined histologically. The muscles of these larvae were vesiculated, irregular in shape, and abnormally dystrophic. Muscle attachment to the cuticle was disrupted as a result of damaged tonofibrillae. The significance of these muscular effects is discussed in relation to the formation of larviform puparia.