Development models

The effects of toxicants on the development of nematodes can be investigated by counting the number of individuals in each stage of their life cycle: egg, L1, L2, L3, L4 and adults, at regular time intervals up to 96 h after treatment. The development through the larval stages can be estimated using the following criteria: L1 if they have four or fewer gonadal cells; L2 if they possess over four gonadal cells which have begun to spread along the length of the animal; L3 if there is a further extension of the gonad, and vulval morphogenesis has started; L4 if there is a dorsal rotation of the gonad; and adults if they have observable eggs. Entrance into the dauer state can be used to analyze toxicity since dauer formation is induced by causing starvation in nematodes. Usually, treated nematodes in state of gravidity are placed on agar plates until laying eggs at 20 °C. This progeny is changed to 27 °C, and 72 h later. The organisms in the dauer stage are counted.