Abstract
Investigations have been made on the arrested development of fully grown larvae of the Indianmeal moth, Plodia interpunctella HÜBNER under the controlled temperature conditions in the laboratory using rice bran as the food of the larvae.
The onset of arrest in this species is governed by the temperature conditions. When they were reared at 30°C from their parental stage up to the egg stage, the 1st, 2nd and 3rd larval stages, and removed into 20°C respectively, all of them entered a state of arrested development at the fully grown stage.
However, when the larvae were removed at the 4th and 5th instar stages, some or no larvae entered an arrested state at the fully grown stage, and the larvae which have no resting stage pupated promptly even under the temperature condition of 20°C and produced adults.
The arrested larvae are not completely inactive, but differ from the non-arrested larvae not only in physiological but also in morphological and behavioristic characters as shown in the table.
When the arrested larvae are removed from 20°C to the high (30°C) temperature condition they pupate promptly without any interruptions.
The arrested larvae, however, show the characteristics, just like “diapause” insects, such as the interruption of pupation at about 20°C, the strong resistance to cold, the chilling effect of 5∼10°C conditions upon the pupation at 20°C.
It is also one of the features of the “diapause” that the stage of arrest is characteristic of the species. In adition to this, the changes of the body weight and the water content of the arrested larvae at about 20°C resemble those which are observed in the “diapause” larvae of insects.
In view of the results described above it can be suggested that the larval hibernation of the Indianmeal moth is not the “quiescence” owing to low temperature but one of the types of “diapause”. This type of diapause can be expected to exist among other insects.
