TOXICITY AND PATHOGENICITY OF METARHIZIUM ANISOPLIAE VAR. ACRIDUM (DEUTEROMYCOTINA, HYPHOMYCETES) AND FIPRONIL TO THE FRINGE-TOED LIZARD ACANTHODACTYLUS DUMERILI (SQUAMATA: LACERTIDAE)

摘要

Reptiles in arid and semiarid zones are frequently exposed to insecticides sprayed to control locusts and grasshoppers. We evaluated the toxicity and pathogenicity of new biological and chemical control agents to the fringe-toed lizard Acanthodactylus dumerili in Mauritania, West Africa. A mycoinsecticide based on spores of the entomopathogenic fungus Metarhizium anisopliae van acridum (isolate IMI 330189, Green Muscle~(~R)) was tested at high challenge concentrations, using three exposure routes. Thirty-minute inhalation exposure to 3.9 X 10~8 viable conidia/L had no adverse effect. Locomotor activity, feeding activity, food consumption, body weight, and liver-to-body weight ratio were similar among treatments. Gross necropsy revealed no pulmonary lesions, hyphal mats, clumps of spores, or other abnormalities associated with fungal infections. Oral exposure to an oil-miscible flowable concentrate administered at approximately 10~7 viable conidia/g body weight had no effect on locomotor activity, food consumption, and body weight of survivors. However, two of the treated lizards died within one week of exposure. Feeding activity (sexes pooled) and relative liver mass of female survivors were significantly reduced. This was also observed in lizards treated with deactivated (nonviable) conidia, indicating an inherent toxicity of the formulation. Limited necropsy examination at four weeks posttreatment revealed that one lizard treated with viable spores had developed a pulmonary mycetoma that contained a clump of viable spores and fungal mycelium. The toxicity of mycotoxins was tested by feeding mycosed nymphs of desert locust Schistocerca gregaria to lizards. An average consumption of 231 mg (females) or 260 mg (males) nymphs/g body weight showed no adverse effect for any of the endpoints. No risk due to the pathogen is anticipated at recommended field application rates. The second agent tested was fipronil (Adonis~(~R)), a phenylpyrazole insecticide. A single dose of 30 μg fipronil/g body weight was administered via contaminated prey or stomach instillation. The percentage of dead or moribund lizards at four weeks posttreatment was 62.5% in animals fed contaminated prey and 42.0% in gavaged animals. In both tests, survivors showed significantly reduced feeding activity, food consumption, body weight, and organ-to-body-weight ratios (liver and/or fat body). The high toxicity of fipronil to lizards was not previously known, suggesting that follow-up studies (e.g., subacute dietary tests) are needed to provide adequate data for risk assessment.