CHANGES IN WEIGHT AND WATER CONTENT DURING THE LIFE CYCLE OF THE WOOD-EATING BEETLE, PASSALUS CORNUTUS FABRICIUS

¹ Department of Zoology, Duke University

The changes in weight and water content from egg to adult have been shown for the wood-eating beetle, Passalus cornutus.

In the egg little change occurs for the first 5 days of development; then the weight of the egg, the volume of the egg, and the amount of water increase steadily until hatching. The increase in weight is due to water uptake. As weight, volume, and water content increase the color of the egg changes from bright red to dark green.

During larval life, which in the laboratory at 27° C. lasts approximately two months, the weight may increase more than 10,000 per cent. A slight fall in weight occurs when the larva ceases to feed and enters the prepupal stage. On emergence of the adult there is a sharp drop in weight amounting to about one-sixth the maximum larval weight.

The water content of a newly laid egg is about 68 per cent. This increases to 83 per cent at time of hatching. Newly hatched larvae contain about 85 per cent water, but after feeding begins this increases to about 90 per cent. A slight fall in percentage of water occurs when the larva ceases to feed, but increases again in the prepupal and pupal stages until, in the late pupa, it reaches a high of 93 per cent. The fall in per cent water is gradual in newly transformed adults and several months may be required for it to reach the level of 67 per cent characteristic of old adults.

The gradual change in water content of the new adults is correlated with the slow increase in dry weight, slow sclerotization of the integument, and with changes in color from red to black.