STUDIES ON THE INFLUENCE OF INANITION ON THE DEVELOPMENT AND THE DURATION OF LIFE IN INSECTS

STEFAN KOPE ¹

¹ GOVERNMENT INSTITUTE FOR AGRICULTURAL RESEARCH, PULAWY, POLAND

1. Intermittent starvation of young caterpillars of Lymantria dispar L. causes considerable prolongation of the larval life as well as a certain abbreviation of the pupal period but has no influence on the duration of life of the imago. These changes increase in proportion as more intense starvation is applied. Larger effects are elicited by longer and less frequent than by more frequent, but shorter, feeding intervals.

2. The differences of results obtained by various authors in regard to the influence of starvation on metamorphosis depend on differences of age of the animals experimented upon. The caterpillars subjected to inanition approximately from the seventh day after their last moult had retarded pupation, whereas this process is accelerated by starvation of animals approximately since the tenth day after the last moult.

3. The development of imaginal discs is not the consequence of histolytical processes which cause pupation of caterpillars, but they take place simultaneously from the first days of larval life. The brain causes, probably by its secretion (or secretions), histolysis of larval tissues and it also seems to check in the caterpillar the development of the imaginal discs.

4. The prolongation of the larval period in starved specimens may be explained by certain disturbances in the hypothetical secretory function of the larval brain, which are caused by inanition; the abbreviation of the pupal stage may be ascribed to analogous decrease of the influence of this organ, which retards the development of imaginal discs.

5. The average limit of larval growth expressed in the average weight of the new-formed chrysalids is in direct proportion to the quantity of food given and inverse to the prolongation of larval and to the abbreviation of pupal life. (The decrease of weight of caterpillars is larger in cases of longer though more rare food-intervals than in cases of more frequent but shorter ones.) These rules may be applied only to differently starved whole experimental materials, having no application to separate specimens of separate broods, both starved and control.

6. The capacity to grow as well as the capacity to undergo metamorphosis exists in starved specimens far beyond the age at which control caterpillars cease to grow and undergo transformation.

7. During long lasting starvation organisms get accustomed to the abnormal conditions: the rate of growth of the caterpillars starved every second day during their whole life becomes in time considerably greater than that of specimens analogically deprived of food since their last moult but one.

8. Hunger death of caterpillars is probably caused first of all by exhaustion of reserve substances. Natural death of the imago probably is a function of the character of metabolism, as death is delayed by the changed metabolism of intermittent starvation.