Piercing Mechanics of Bed Bug Tarsi
The mechanical properties of bed bug (Cimex lectularius L.) tarsi were investigated in order to evaluate their vulnerability to piercing by plant trichomes (sharp microscopic hairs). This information will help inform development of physical methods for control of insect pests such as bed bugs. Nanoindentation was used to measure the force required to insert a sharp probe into the cuticle of the tarsi in different regions, as well as to determine creep and reduced elastic moduli for the cuticle. Scanning electron microscopy was used to visualize the indents that had been generated by nanoindentation. Scanning electron microscopy was also used to visualize the process of indent formation while poking the cuticle with a nanomanipulator. Focused ion beam milling was used to determine cuticle thickness for different regions of the tarsi. The force required to insert a sharp object into the cuticle of the tarsus was determined for depths ranging from 1 to 9 microns at strain rates ranging from 0.003 to 0.5 s-1. Greater force was required to insert a sharp object at greater depth or at faster strain rates. A specific region of the pretarsal claws (membrane with microtrichia) was more frequently pierced by trichomes during bed bug locomotion, and was more easily pierced, exhibited more creep, and had a lower reduced elastic modulus. The combination of these mechanical attributes, in addition to the presence of natural infoldings in the cuticle of this area, make the membrane with microtrichia of the pretarsal claws particularly vulnerable to piercing.