MOULTING HORMONE ACTIVITY IN THE ADULT COLORADO POTATO BEETLE,<i>LEPTINOTARSA DECEMLINEATA</i>SAY IN RELATION TO REPRODUCTION AND DIAPAUSE

Abstract

Ecdysteroid levels in Leptinotarsa decemlineata were measured by radioimmunoassay (RIA), using an antiserum with a 10 times higher affinity for ecdysterone than for ecdysone and polyethylene glycol as a means for separating free from bound hormone. In reproducing males, raised under long day conditions (LD: 16 h photophase, 25°C) there was a peak of 54 ng/g at day 3–4, declining thereafter to very low values. In LD-females, 50 ng/g was found at day 2 (just before the onset of vitellogenesis), decreasing to 20 ng/g at day 5 (start of oviposition) and increasing again thereafter to 95 ng/g at day 14. In prediapausing animals, raised under short day conditions (SD: 10 h photophase, 25°C) the level was practically the same in both sexes and it was significantly higher than in reproducing animals. In both sexes a peak of about 96 ng/g was found from day 2 to 4, thereafter the level dropped quickly. During diapause the level increased slowly and in 9 month diapausing adults it was about 75 ng/g. This is the first time that high ecdysteroid levels are reported in relation to diapause induction in an adult insect, and the first time that high levels are found in adult males, indicating that the ovary cannot be the only site of synthesis of moulting hormone. The content during metamorphosis was also determined, mainly as a test for our RIA method. Hitherto there was no indication whatsoever that moulting hormone (MH) might be present and play a role in the adult stage in this insect. Our results make necessary a reappraisal of the hormonal regulation of oogenesis and induction of diapause in the Colorado beetle. The nature of the ecdysteroids present in the adult stage, their site of synthesis, their metabolism and physiological significance remain to be determined.