Abstract

Direct radiochemical determinations of juvenile hormone (JH) biosynthesis by corpora allata (CA) isolated from starved and re-fed Periplanteta americana have been employed to elucidate the humoral mechanisms involved in the modulation of reproductive activity in response to food availability. When starvation was initiated in mature adult females at the time of formation of an oötheca the next oötheca was normally deposited 5 to 6 days later, a delay of 2–3 days, and a third oötheca was formed by only 50% of starved females. The terminal oöcytes in the remaining females were either resorbed or maintained in an arrested state. Ovarian development had effectively ceased after 2 weeks of starvation but recommenced within 3 days of re-feeding. The CA of most starved females exhibited 2 activity cycles following food withdrawal. The first peak occurred on day 1 of the starvation period and was coincident with the timing for fed controls. The second peak was delayed by about 2 days and the activity of the CA then declined to the extent that glands from animals starved for more than 11 days were completely inactive. Feeding, after 10 or 16 days starvation, resulted in a resumption of CA activity which was detectable in some animals within 24 hr, and very high rates of JH biosynthesis were found 4 or 5 days later. The results suggest that P. americana can readily and efficiently modulate egg production in response to food supply, and that control is effected through alterations in JH production by the CA. The use of farnesenic acid as a biochemical probe indicates that CA inactivity after long periods of starvation does not arise because malnutrition has caused complete metabolic shut-down in the glands, and that JH biosynthesis is basically modulated at a control point prior to the last two enzymic stages in the pathway.

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