The lowest weight at which a final instar larva of the leafroller, Cnephasia jactalana (Walker) (Lepidoptera: Tortricidae) can initiate pupation, the larval critical weight, was unaffected by diet quality. Use of a non-nutritive artificial diet showed that the larval-pupal metamorphosis was possibly triggered by stretch receptors, and was not related to nutrition per se. However, a final-instar larva was not able to moult until it had ingested and assimilated the quantity of food required to attain the larval critical weight. The period between attaining the larval critical weight and the larval maximum weight is the latent feeding period which was found to be longer on higher-quality diets. The decrease from larval maximum weight to pupal weight depended on diet quality: optimum-quality diets gave the smallest decreases. The decrease from pupal to adult weight was not affected by diet. Reproductive performance was strongly affected by the quality of the diet during the latent feeding period.
