New findings on the functional morphology of the male genitalia of the blood-feeding bug Rhodnius prolixus in the light of a different observation on living tissue.

Among insect species, the male genitalia evolved many different anatomical features to ensure reproductive success. Males of primitive insects do not copulate but transfer sperm packaged in a spermatophore to the female, whereas males of the most advanced insects copulate and deliver free sperm to the storage organ, the spermatheca, in the female reproductive tract. Based on previous studies on several species of triatomine bugs (Rhodnius prolixus included), Triatominae are thought to use an intermediate form of sperm transfer in which the male genitalia have evolved to carry out both copulation and spermatophore formation. Previous observations on chemically fixed tissue of R. prolixus appear to show that the penis, the aedeagus, contains a much-folded internal cuticle which is a collapsed sac that everts from the aedeagus during copulation for the formation and delivery of the spermatophore directly to the female genital chamber. However, observations on living tissue of these structures in R. prolixus show that this internal cuticle functions as a tube through which male secretions pass through the aedeagus to the vagina. The organization of this cuticle in the context of the various anatomical structures of the aedeagus, its different morpho-functional meaning during sperm transfer in R. prolixus, the use of living versus chemically fixed tissue and a new understanding of previous observations are discussed.

Reproductive physiology in the blood feeding insect, Rhodnius prolixus, from copulation to the control of egg production.

The study of copulation and the control of egg production in the blood-feeding insect, Rhodnius prolixus, continues to offer a fertile ground for the cultivation of new insights into the physiological processes associated with reproduction. We begin this paper by describing the male organs of copulation showing that the aedeagus contains a structure which may serve as part of a pumping mechanism or valve to enable the male to fully pack the vagina with his secretions. We then summarize previously published work which identifies possible sensory and chemical aids that can be used by the male as he forms a naked spermatophore within the vagina of the female. With respect to the control of egg production, published anatomical and endocrinological experiments give rise to the intriguing possibility that a vascular portal system exists in the head of this insect, and that this system explains why circulation is required for egg production. By documenting the steps taken by the male during copulation, and by providing a new paradigm to explain the control of egg production, this paper identifies some assumptions that need verification, and offers a foundation upon which future scientists can explore reproductive physiology in this incredible bug.

Feeding through artificial membranes reduces fecundity for females of the blood-feeding insect, Rhodnius prolixus.

The blood-feeding insect, Rhodnius prolixus, has been raised in the laboratory for close to 100 years. Various feeding techniques have been employed ranging from the use of warm-blooded hosts, to the use of previously collected blood offered through artificial membranes. This study compared the fecundity in mated and unmated females fed rabbit blood directly from the shaved belly of a rabbit to that of females fed defibrinated rabbit blood through an artificial membrane. These results confirm previous reports that this insect's feeding efficacy is reduced using an artificial membrane. It also demonstrates for the first time that the fecundity index, which measures the efficiency of turning the blood meal into eggs, is significantly reduced. We suggest that the natural feeding on a warm-blooded host may provide cues that have the short-term effect of enhancing the act of feeding and the long-term effect of increasing egg production efficiency. Until an artificial feeding method that does not interfere with feeding and fecundity is devised, experiments on reproduction in R. prolixus warrant the use of a warm-blooded host to emulate feeding in its natural setting.