Ecdysteroid and free amino acid content of eggs of the Colorado potato beetle, Leptinotarsa decemlineata.
In order to identify components of the Colorado potato beetle (CPB) egg that may be required by Edovum puttleri, a parasitic wasp that parasitizes the CPB egg, to complete development, ecdysteroid and free amino acid content of CPB eggs were analyzed by reversed phase high pressure liquid chromatography followed by radioimmunoassay to identify ecdysteroids. Ecdysteroid titers were relatively low (<300 pg/egg) through day 2 post-oviposition and then increased sharply, reaching concentrations >2,500 pg/egg on day 3 post-oviposition. Ecdysone (E), 20-hydroxyecdysone (20E), and polar conjugates of E were prominent ecdysteroids present in eggs sampled on days 0 and 1 post-ecdysis, and E, 20E, three peaks containing more polar ecdysteroids (metabolic inactivation products), and polar conjugates of E were present in eggs sampled on day 2. Thus, at a time when parasitization of CPB eggs by E. puttleri is relatively high (0-48 h), physiologically-active ecdysteroids (20E and perhaps E are physiologically active) are present at concentrations between 50 and 200 pg/egg. Ecdysone and 20E reached their highest levels in day-3 eggs, indicating that ecdysteroid may direct physiological processes associated with the completion of CPB embryonic development. In day-4 eggs, the concentration of E and 20E fall dramatically and polar metabolites of E and/or 20E are now responsible for the high ecdysteroid content of the eggs. Interestingly, conjugates of E decrease to relatively low levels in day-3 eggs and are absent in day-4 eggs. Therefore, it is likely that the increase in E in day-3 eggs is due, in part, to the breakdown of polar conjugates of E. Nine amino acids were present in significant quantities in eggs sampled at various times between 0 and 48 h post-oviposition. These include histidine, glutamine, proline, asparagine, serine, glutamic acid, threonine, lysine, and tyrosine. The first three amino acids were present at concentrations that were approximately 2 to 6 times greater than the concentrations of the last six amino acids. Amounts of most of the free amino acids varied with the age of the eggs from which the extract was prepared, but in general, there was no correlation between the levels at times of maximum parasitization (0 and 30 h) and the levels at the less favored times of parasitization (16 and 48 h). This information should facilitate the development of diets for both parasites and predators of pest species of beetles. Arch. Insect Biochem. Physiol. 44:172-182, 2000. Published 2000 Wiley-Liss, Inc.