PESTICIDES AS CHEMICAL-AGENTS INDUCING HELMET FORMATION IN DAPHNIA-AMBIGUA

1. Daphnia ambigua was exposed to harmful concentrations of pesticides (six insecticides, two herbicides, one fungicide) for 10 h from the final embryonic stage to the first instar, and effects on morphology were investigated. 2. The animals developed helmets at the second instar after exposure to the insecticides, but did not show the same response when exposed to the herbicides and the fungicide. 3. Some stimuli due to the insecticides on the nervous system of the animals may switch on the formation of the helmet, an antipredator morphology, which originally evolved as a response to chemicals released by predators. 4. lt is suggested that a range of chemicals other than the predator/prey kairomone can induce the helmet formation in Daphnia.