Enzyme immunoassay measurements of ecdysteroids in the last larval stage of Culex pipiens L. (Diptera, Culicidae): Hormonal profile and correlation with cuticle secretion

Abstract

The molting hormone (ecdysteroids) in whole body extracts of 4th-instar larvae of Culex pipiens L. (Diptera, Culicidae) was measured by an enzyme-immunoassay (EIA) using two specific antibodies, the rat monoclonal EC 19 antibody showing a high affinity for 20-hydroxyecdysone (20E) and the rabbit polyclonal B antibody six times more sensitive to ecdysone (E) than to 20E. EIA measurements revealed the presence of the two main hormones seen in C. pipiens: E (ca. 30 %) and 20E (ca. 70 %). Furthermore, change in ecdysteroid amounts during the 4th-larval stage was down using only a rat monoclonal because 20E was the major hormone. The ecdysteroid amounts presented a single peak that occurred at day three during the last larval development. In a second series of experiment, the cuticle cycle was determined by a histological study of the larval integument in order to establish temporal correlations with the hormonal levels. Thus, the ecdysteroid peak recorded during the last larval stage coincides with the apolysis and could be related with the induction of a new cuticle secretion.

Key words: Mosquitoes, Culex pipiens, hormone, ecdysteroids, enzyme-immunoassay (EIA), histology, cuticle.