New Anatomical Evidence from the Male Asian Citrus Psyllid (Hemiptera: Liviidae) Invokes Controversy Over the Accepted Function of Some Male Reproductive Organs in Psylloidea

Abstract

Males of many Psylloidea are known to possess a characteristic structure at the functional hub of their reproductive apparatus, between afferent and efferent passage of seminal fluid. The structure is a squat, cylindrical endoskeleton consisting of two sections. Classical authors named them as ‘sperm pump’ and ‘ejaculatory duct’, based on superficial resemblance to a spring-loaded, thimble-shaped cylinder, encircled by smooth, vertical columns interpreted to be muscles which, when contracted, compress the cylinder and affect seminal fluid discharge. The discovery of numerous spherules of unknown composition and function in and around the columns of the Asian citrus psyllid male genitalia invoked rigorous scrutiny of the classical literature for evidence to support its claims, and determined that the grounds for vetting the structure as a sperm pump were fully teleological. This paper raises several objections to modern acceptance of this classical interpretation, presenting them as problematic, thought-provoking, and sometimes controversial anatomical features. The two sections are herein called ‘drum’ and ‘spout’. As an endoskeleton, the sections are an invagination of the exoskeleton and therefore cannot receive seminal fluid into their hollow. A phallus is identified inside an aedeagal tube, indicating that it is the ejaculatory duct—the tube, drum, and spout are considered its housing. A sheath envelopes the drum and is directly continuous with the spout hypodermis, another problematical feature raising the question of whether it is detached from adherence to the drum cuticles. Also, there are four afferent tubes but only two openings in the drum to receive their seminal fluids.