Pesticides are known to transform in the environment, but so far the study of their effects in the environment has concentrated on the parent compounds, thereby neglecting the effects of the degradation products. The embryotoxic, developmental, and teratogenic effects of chloroacetanilide herbicides and their environmentally stable aniline degradation products were investigated in this study in view of the massive application of alachlor and metolachlor. Embryos at midblastula to early gastrula stages of a locally abundant African clawed frog Xenopus laevis were used as test organisms. The embryos were exposed to the test chemicals for 96 h in each experiment. Alachlor is more embryotoxic (the concentration causing 50% embryo lethality, 96-h LC50 = 23 microM [6.1 mg/L]) and teratogenic (teratogenic index [TI] = 1.7) than metolachlor (96-h LC50 = 48 microM [13.6 mg/L], TI = 0.2). The degradation products of alachlor and metolachlor, respectively, 2,6-diethylaniline (96-h LC50 = 13 microM [19.4 mg/L], TI = 2.1) and 2-ethyl-6-methyaniline (96-h LC50 = 509 microM [68.8 mg/L], TI = 2.7), are less embryotoxic but more teratogenic than their parent compounds. The most common teratogenic effects observed were edema for alachlor as opposed to axial flexures and eye abnormalities for 2,6-diethylaniline and 2-ethyl-6-methylaniline. Metolachlor is found to be an example of a nonteratogenic herbicide that upon degradation loses toxicity but gains teratogenicity, and both the herbicides, metolachlor and alachlor, are potential sources of teratogenic transformation products.
A tick assembly pheromone present in the excretory waste product of the soft tick, Ornithodoros porcinus porcinus (Walton), has been separated by high performance liquid chromatography (HPLC). It has been identified as guanine on the basis of absorption and mass spectral data, and bioassays using nymphs of Argas persicus (Oken). Guanine was active at a low concentration of 8 × 10 −12 M/cm 2 of filter paper. Guanine was shown to induce assembly in Amblyomma cohaerens Donitz larvae and Rhipicephalus appendiculatus Neumann adults.Various purines and ammonium salts tested in the assembly bioassay, and with exception of adenine, were shown to be active for A. persicus.
The assembly behavior of the tickArgas persicus Oken in response to guanine has been found to be humidity dependent. Nymphal and adult maleA. persicus assemble on guanine-treated paper disks only at low relative humidities (25 ± 5%). Exposure of the ticks to high relative humidities (85 ± 5%) results in a gradual induction of a negative response to the pheromone.
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