Cytochrome oxidase activity during diapause and metamorphosis of the Japanese beetle, Popillia japonica Newman.

1. Determinations were made on the activity of cytochrome oxidase of individual Japanese beetles during growth, diapause, and metamorphosis. All readings were made on homogenates at a dilution of 1:1,000, except for adult beetles, when the final dilution was 1:10,000. 2. The activity of the enzyme increased during larval growth from a low value of 0.022 in the second instar, to high values ranging from 0.074 to 0.083 in diapause third instar larvae. 3. The high activity of cytochrome oxidase during larval diapause indicates that this condition may be physiologically different from that occurring in the egg or pupal stages of most other insects. 4. During metamorphosis, the activity of cytochrome oxidase follows the characteristic U-shaped curve associated with respiratory metabolism. It thus appears that most of the oxidation occurring in metamorphosing individuals is mediated through the cytochrome system. 5. The activity of cytochrome oxidase is significantly higher in the adult male than it is in the adult female; the values (calculated on the basis of a 1:1,000 dilution) were 0.40 +/- 0.028 and 0.25 +/- 0.012, respectively.