Testicular oocyte development and other toxic effects in the common hourglass tree frog exposed to three commercial insecticide formulations

The endocrine-disrupting effects of insecticides on wildlife have received increasing attention in the literature in recent years. Here we tested the lethal and sub-lethal effects of three commercial insecticide formulations of profenofos, carbosulfan, and diazinon on the common hourglass tree frog, Polypedates cruciger, under laboratory conditions. Acute and chronic exposures to the three chemicals on the survival, growth and development of malformations were studied. The acute toxicity (at Gosner stages 23, 25 - 26, and 31) in terms of LC₅₀ was highest in profenofos followed by diazinon and lowest in carbosulfan. Chronic exposure (at Gosner stage 25) to environmentally relevant concentrations of three insecticides showed a reduction in the survival of the tadpoles. It also affected the growth where the exposed individuals were smaller and took longer to metamorphose than unexposed tadpoles. Histological preparations of the testes of male frogs exposed to all three insecticides developed oocytes, reporting a profound effect in carbosulfan exposure. The concentrations of more than 2 ppb caused oocyte development in 100% of the exposed frogs. However, none of the chemicals induced any external malformations. These laboratory findings highlight the importance of examining the frogs in chemically contaminated environments for testicular oogenesis, leading to demasculinization of male frogs.