Attachment force (mN) of bed bugs Cimex lectularius males on Perspex (PMMA) in relation to surface roughness and wettability

Insects attach to various surfaces that differ, among others, in roughness and wettability. Identifying surface characteristics that allow or prevent insects from attaching is an important research avenue of pest control. Here we take an experimental approach to analyse the attachment of common bed bugs, Cimex lectularius Linnaeus (1758), to Perspex (PMMA) substrates. We construct a reliable centrifuge device that allows the measurement of attachment forces at substrate roughnesses, Ra, between 0.02 and 1.3 µm and at two wettabilities. Our results suggest that bed bug attachment to surfaces is minimal at a substrate roughness of 0.2 and 0.4 µm on normal PMMA, where the lowest attachment force was 0.8 mN and the safety factor 15. At lower and higher roughness, attachment forces were higher and the safety factor increased to a maximum of 133. On PMMA that was made superhydrophobic by spray-coating, the attachment was lowest (0.2 mN) at the lowest roughness and continuously increased with increasing roughness, reaching 2.5 mN and a safety factor of 46. For every roughness, attachment forces were lower on superhydrophobic than on normal PMMA. This knowledge may inspire the development of repelling substrates for bed bug control.

Methods
We designed a custom-made device incorporating a laser, phototransistor, and reed switch centrifugal method for measuring the attachment force.

A bed bug was placed onto the disc, more than 10 mm from the centre of the circle. Each of the ten males examined was tested on all PMMA surfaces at 22-23 °C and 45 % relative humidity. Each bed bug was tested five times consecutively on each surface but there were at least 24 hours between each surface testing. We used the maximum force of five attachment trials, rather than the mean. In total, 500 individual tests were carried out and statistically evaluated using the SigmaPlot 12.0 software (Systat Software, Inc.).

The disc constantly accelerated until the bed bug was no longer able to adhere. The maximum speed achieved was approximately 1600 rpm. The radius, r, of the position of the insect was recorded at the point of release. The radius, together with the rotational speed (number of rotations per unit time), and the mass, m, of the bed bug allowed the calculation of the force that is required for it to be displaced from the disk (attachment force F). F was determined from the angular velocity, ω (the rate of change of angular displacement per unit of time), at which the bug was detached from the disc, its mass, m, and the radius (F=m r ω 2).