| Summary: | Application of the organophosphorus insecticide temephos to a natural pond in central Minnesota was followed by reduction within 24 hr in all cladocerans, in Diaptomus leptopus and in Chaoborus americanus, and increases in cyclopoid copepods, copepod nauplii and rotifer Keratella cochlearis. aphnia ulex that reappeared 35 days post-application were ex-ephippial. fter application, reproduction of cladocerans and Diaptomus was markedly reduced compared to the previous year, an effect attributed to temephos. aphnia population density was strongly reduced into the fall season, long after the spring applications, compared with both a reference pond's and the previous season's populations. On-site bioassays demonstrated 24-hr mortalities of Daphnia and Chaoborus that were comparable to the population decreases in the pond. aboratory toxicity tests showed Daphnia was the most sensitive followed by Chaoborus and Diaptomus. Comparable results were seen in the pond population changes, in situ bioassays arid laboratory toxicity data for Daphnia and for Chaoborus but sensitivities in the pond were somewhat greater than in the laboratory. isk assessment research calls for long-term field reproduction analysis to avoid a false "recovery" report, combined with laboratory life cycle analysis and short acute exposure tests.
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