Amphibian populations are declining globally, and pesticides have been suggested as one of the contributing factors. Field experiments involving ponds immersed in agricultural environments have been observed to have dramatically lower biodiversity and amphibian abundance than ponds located in non-agricultural settings. There has been much work involving in situ pond experiments, and a plethora of laboratory pesticide experiments often involving test concentrations much higher than those observed in the field. To determine which pesticides impact amphibian embryo survivorship and tadpole development, three insecticides currently used in British Columbia were tested at their detected field concentrations in a laboratory environment. The commercial formulations of endosulfan, azinphos-methyl and diazinon were tested alone and in combination. Embryos of the Great Basin Spadefoot (Spea intermontana and Pacific Treefrog (Pseudacris regilla) were collected from reference sites in the South Okanagan of BC, and transported to a federal government laboratory facility in North Vancouver, BC. Here, 8-day LC20 experiments were conducted on the young embryos and young tadpoles with the following toxicological endpoints: acute mortality, behavioral abnormalities, morphological abnormalities and developmental abnormalities. Overall, endosulfan (LC20₈d = 77.1 ng/L) was the most toxic pesticide to both species in the tadpole stage, causing acute mortality, behavioral abnormalities and morphological abnormalities. Embryos were observed to be very resilient to the low test concentrations of endosulfan, with the majority of mortalities occurring post-hatch (LC20₈d = 2872.7 ng/L). The second most toxic insecticide was found to be azinphos-methyl (LC20₈d > 50 000 ng/L); and lastly, diazinon was found to be the least toxic (LC20₈d > 175 000 ng/L) to both life stages of amphibians. In addition to acute mortality, several behavioral abnormalities arose in the tadpoles exposed to endosulfan, including extreme agitation in both species of amphibians, tail kinking and melanophore aggregation in P. regilla tadpoles.

Amphibian populations are declining globally, and pesticides have been suggested as one of the contributing factors. Field experiments involving ponds immersed in agricultural environments have been observed to have dramatically lower biodiversity and amphibian abundance than ponds located in non-agricultural settings. There has been much work involving in situ pond experiments, and a plethora of laboratory pesticide experiments often involving test concentrations much higher than those observed in the field. To determine which pesticides impact amphibian embryo survivorship and tadpole development, three insecticides currently used in British Columbia were tested at their detected field concentrations in a laboratory environment. The commercial formulations of endosulfan, azinphos-methyl and diazinon were tested alone and in combination. Embryos of the Great Basin Spadefoot (Spea intermontana and Pacific Treefrog (Pseudacris regilla) were collected from reference sites in the South Okanagan of BC, and transported to a federal government laboratory facility in North Vancouver, BC. Here, 8-day LC20 experiments were conducted on the young embryos and young tadpoles with the following toxicological endpoints: acute mortality, behavioral abnormalities, morphological abnormalities and developmental abnormalities. Overall, endosulfan (LC20₈d = 77.1 ng/L) was the most toxic pesticide to both species in the tadpole stage, causing acute mortality, behavioral abnormalities and morphological abnormalities. Embryos were observed to be very resilient to the low test concentrations of endosulfan, with the majority of mortalities occurring post-hatch (LC20₈d = 2872.7 ng/L). The second most toxic insecticide was found to be azinphos-methyl (LC20₈d > 50 000 ng/L); and lastly, diazinon was found to be the least toxic (LC20₈d > 175 000 ng/L) to both life stages of amphibians. In addition to acute mortality, several behavioral abnormalities arose in the tadpoles exposed to endosulfan, including extreme agitation in both species of amphibians, tail kinking and melanophore aggregation in P. regilla tadpoles.

Amphibian populations are declining globally, and pesticides have been suggested as one of the contributing factors. Field experiments involving ponds immersed in agricultural environments have been observed to have dramatically lower biodiversity and amphibian abundance than ponds located in non-agricultural settings. There has been much work involving in situ pond experiments, and a plethora of laboratory pesticide experiments often involving test concentrations much higher than those observed in the field. To determine which pesticides impact amphibian embryo survivorship and tadpole development, three insecticides currently used in British Columbia were tested at their detected field concentrations in a laboratory environment. The commercial formulations of endosulfan, azinphos-methyl and diazinon were tested alone and in combination. Embryos of the Great Basin Spadefoot (Spea intermontana and Pacific Treefrog (Pseudacris regilla) were collected from reference sites in the South Okanagan of BC, and transported to a federal government laboratory facility in North Vancouver, BC. Here, 8-day LC20 experiments were conducted on the young embryos and young tadpoles with the following toxicological endpoints: acute mortality, behavioral abnormalities, morphological abnormalities and developmental abnormalities. Overall, endosulfan (LC20₈d = 77.1 ng/L) was the most toxic pesticide to both species in the tadpole stage, causing acute mortality, behavioral abnormalities and morphological abnormalities. Embryos were observed to be very resilient to the low test concentrations of endosulfan, with the majority of mortalities occurring post-hatch (LC20₈d = 2872.7 ng/L). The second most toxic insecticide was found to be azinphos-methyl (LC20₈d > 50 000 ng/L); and lastly, diazinon was found to be the least toxic (LC20₈d > 175 000 ng/L) to both life stages of amphibians. In addition to acute mortality, several behavioral abnormalities arose in the tadpoles exposed to endosulfan, including extreme agitation in both species of amphibians, tail kinking and melanophore aggregation in P. regilla tadpoles. / Land and Food Systems, Faculty of / Graduate

Thesis (M.S.)--East Tennessee State University, 2001. / Original full text available electronically. Includes vita. Includes bibliographical references (leaves 54-58) and abstract.

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Specimens from the National History Museum, London, and from the United States National Parasite Collection, Beltsville, United States of America., which had all previously been identified as Mescoelium monas from a variety of definitive hosts (amphibians, reptiles and/or fish), were evaluated using all available literature and the body-type keys developed by Norman Dronen. None of these 85 putative M. monas specimens appeared to fit the original description of M. monas. There are likely multiple species of Mescoelium worldwide, and the M. monas complex, as currently defined, is not a unified monospecific grouping. The present study leads to the conclusion that there can be no fewer than 9 species of Mescoelium (6 body types, 3 of which can be divided into 2 separate groups based on the median or submedian placement of the genital pore). The specimens of M. monas I examined represented 3 of the 6 body types identified by Norman Dronen: the M. monas body type, the M. lanceatum body type, and the M. pesteri body type. Because Mesocoelium is a difficult group within which to distinguish species, it may be expedient in endoparasitic surveys of amphibians, fish and reptiles to consider any specimen of Mesocoelium found to be M. monas. Because Mesocoelium is a difficult group within which to distinguish species, it may be expedient in endoparasitic surveys of amphibians, fish and reptiles to consider any specimen of Mesocoelium found to be M. monas. Subsequent reevalations must consider these key characteristics: genital pore placement, cecal length, vitelline follicle distribution, along with other supporting characteristics.