The puncture mechanics: an example from the bed bug Cimex lectularius showing traumatic insemination using the paramere

Cimicidae are well-known for traumatic insemination, and males pierce
females with their parameres and transfer sperm through them. The shape of
parameres is relatively stable in the family, but in some genera the
paramere is elongated, appearing less resistant against lateral
deflection. To understand the mechanical limitations of the paramere, we
studied its penetration mechanics of the common bed bug, Cimex
lectularius. We examined the postabdominal morphology, paramere geometry,
and material properties and conducted breaking stress experiments on the
paramere under wet and dry conditions. Mechanical property gradients are
present with the paramere tip as the stiffest region and the base as the
most flexible one. These mechanical properties relate to the presence of
Ca, Zn, and Si. The basal wing-shaped structure is flexible, enabling it
to interlock with the anal region during mating. The paramere is slightly
twisted; the tip region is circular in cross-section, and the geometry of
the rest is rather complex. In the mechanical test, wet parameres mainly
buckled, while dried parameres broke off. The level of structural failures
depended on the directions from which the compression forces were applied.
Structural, material, and mechanical strengthening mechanisms preventing
the paramere from mechanical failure are discussed.