7 – The Role of Ecdysteroids in Reproduction

In female insects, the steroid hormone 20-hydroxyecdysone (20E) plays a major role in activating vitellogenesis, a process required for egg development. By contrast with vertebrates, production of large amounts of hormonal steroids has not been reported in adult male insects. In the present study, we analyzed steroidogenesis in both male and female adult of the malaria mosquito Anopheles gambiae and we found that A. gambiae male mosquitoes produce high amounts of the steroid hormone 20E. Importantly, we found that male accessory glands, but not testes, are the source of 20E. Moreover, this steroid hormone is stored in male accessory glands and delivered to females during mating. These findings suggest that male 20E may not act as a true male sex steroid, but more likely as an allohormone. Our results give new insights into species-specific physiological processes that govern the reproductive success of the malaria mosquito. This could thus lead to the identification of new target genes for manipulating male and/or female reproductive success, a promising way to reduce or eliminate mosquito population and therefore to control malaria transmission.

https://www.pnas.org/content/pnas/105/50/19631.full.pdf

Anopheles gambiae males produce and transfer the vitellogenic steroid hormone 20-hydroxyecdysone to females during mating

Publisher Summary Regulation of insect reproduction, involves numerous factors such as sensory receptors, and neuronal transmission and integration in the brain. These factors regulate the synthesis of two groups of insect hormones—the juvenile hormones (JH) and the ecdysterones—along with the production of their own neurohormones. The main reproductive events include sex determination, gonial mitoses, meiosis onset, differentiation of reproductive organs (gonads, ducts and accessory glands), spermatogenesis, previtellogenesis and vitellogenesis, accessory gland functioning, pheromone production, sexual behavior, mating, ovulation, oviposition, incubation of embryos or larvae, and parturition. The reproductive steps depend on mating, which allows fertilization of the oocytes by the spermatozoa, and in addition, triggers oocyte development, egg-laying, and monogamy, by enabling the transmission of male active peptides to the female. The steroid hormones and JH play a major role in various stages of reproduction. JH mostly triggers the functioning of organs. Ecdysone or ecdysterone is mostly involved in morphogenetic processes. Several feedback mechanisms help to regulate reproduction in various ways: these include the action of mature eggs on the functioning of the corpora allata and ovarian follicle, and the action of ecdysterone on the neurosecretory cells of the brain. Other chemical regulators which come from the accessory male glands or are produced by the female during copulation intervene actively in female reproduction, as they regulate oogenesis, egg-laying and sexual receptivity.

Insect Reproduction: Regulation of Successive Steps

Testes of last-instar larvae of the tobacco budworm release five times more ecdysteroid into incubation medium (judged by radioimmunoassay) in 2.5 hours than is found in testis homogenates. Incubation of testicular components indicates that the testis sheath may be the site of ecdysteroid synthesis. Fractionation of hemalymph, testis homogenate, and incubation medium by high-performance liquid chromatography produces a distinct ecdysteroid pattern in each case. Thus, released testis ecdysteroids are probably converted to other forms for use, sequestration, or general circulation. Their functions are unknown.

https://science.sciencemag.org/content/sci/218/4575/896.full.pdf

Larval testes of the tobacco budworm: a new source of insect ecdysteroids.

"Insects do not have sex hormones": a myth?

Male adult blowflies contain ecdysteroids. A considerable amount of ecdysteroid is concentrated in the testes and gives rise to a high local concentration. Analysis by high performance liquid chromatography and thin-layer chromatography indicate that ecdysterone is the most prominent ecdysteroid in male flies. The results can explain several hormone-dependant processes.

J. Koolman

Papers

Ecdysteroids in the adult male blowflyCalliphora vicina