Imidazole derivative KK-42 reduces ecdysteroid titers and interferes with reproductive processes in adult females of Tenebrio molitor

KK-42, an imidazole derivative considered as potent inhibitor of ecdysteroid biosynthesis, was tested on adult females of Tenebrio molitor. The compound was applied topically (0.1, 1, 5, and 10 μg/insect) on 0- or 2-day-old adult females or added to the culture medium (1 and 10 μM) of ovaries. To test the effect of KK-42 on the reproduction capacity, ovaries were explanted from 2- and 4-day-old females corresponding, respectively, to follicles at the beginning and the end of vitellogenesis. KK-42 treatment reduced the fecundity and the longevity of females, and in addition, it delayed oviposition and affected growth and development of oocytes as evidenced by measurements of the ovarian weight, the number of oocytes per ovaries, and the size of the basal follicle. Hence, the effects were stronger in newly emerged females compared to 2-day-old females. Interestingly, RH-0345, an ecdysteroid agonist, could partly restore the effects on reproductive events induced by KK-42. In a second series of experiments using an enzyme immunoassay to measure ecdysteroid titers, KK-42 reduced the amounts of ecdysteroids in ovaries after application on newly emerged adult females. In 2-day-old females, it caused a significant effect with the highest doses. In addition, the compound significantly reduced the amounts of ecdysteroid released into the culture medium by ovaries explanted from 2- or 4-day-old females. The results are discussed in relation to the mode of action of KK-42 on reproduction. © 2004 Elsevier Inc. All rights reserved.