The Male Reproductive System of the Kissing Bug, Rhodnius prolixus Stål, 1859 (Hemiptera: Reduviidae: Triatominae): Arrangements of the Muscles and the Myoactivity of the Selected Neuropeptides

SIMPLE SUMMARY: The kissing bug, Rhodnius prolixus, is a blood-gorging insect that is medically important, being a principal vector of Trypanosoma cruzi, which causes Chagas disease. Understanding the reproductive biology of R. prolixus is, therefore, of some importance from a scientific perspective, but also in the medical context in order to control the spread of the disease. Here we show that the male reproductive system of R. prolixus is composed of muscular tissues performing contractions that aid in the transfer of sperm and other fluids into the female during mating. These contractions are further shown to be controlled by neuropeptides released by the nervous system that act on the receptors to either increase or inhibit the contractions. The male reproductive structures are, therefore, coordinated for successful copulation, whereby the transfer of sperm and fluid occurring during copulation is facilitated through a coordination of the contraction of the muscles within the male reproductive system. This study is critically important to provide novel options for pest management. ABSTRACT: The gross anatomy of the male reproductive structures and their associated musculature are described in the blood-gorging vector of Chagas disease, Rhodnius prolixus. The male reproductive system is composed of muscular tissues each performing contractions that aid in the movement of sperm out of the testis into the vas deferens, seminal vesicle and then into the ejaculatory duct, along with proteins and lipids from the transparent and opaque accessory glands. Phalloidin staining shows the various patterns of muscle fiber layers, from thin circular to more complex crisscross patterns, implying subtle differences in the form of the contractions and movement of each of the structures, allowing for waves of contractions or twisting patterns. The transcripts for the receptors for proctolin, myosuppressin (RhoprMS) and for the extended FMRFamides are expressed in the various regions of the reproductive system, and the nerve processes extending over the reproductive structures are positive for FMRFamide-like immunoreactivity, as are neurosecretory cells lying on the nerves. Proctolin and AKDNFIRFamide are strong stimulators for the frequency of the contractions, and RhoprMS can inhibit the proctolin-induced contractions. Taken together, this work implicates these two families of peptides in coordinating the male reproductive structures for the successful transfer of sperm and the associated accessory gland fluid to the female during copulation.