How tight are beetle hugs? Attachment in mating leaf beetles.

Area of Science:

• Entomology
• Biomechanics
• Sexual Selection

Background:

• Leaf beetles, including Chrysolina americana (rosemary beetles), display sexual dimorphism in tarsal attachment setae.
• Male rosemary beetles possess unique setal discoid terminals, hypothesized to facilitate long-term attachment to female elytra during copulation and mate guarding.

Purpose of the Study:

• To investigate the attachment capabilities of living male and female rosemary beetles on female elytra.
• To quantify the pull-off forces and compare attachment strength between sexes and substrates.

Main Methods:

• Utilized a custom-made tribometer with a self-aligning sample holder for pull-off force measurements.
• Tested attachment strength of live male and female beetles on both female elytra (convex) and flat glass substrates.

Main Results:

• Both male and female beetles demonstrated significantly stronger attachment to female elytra (45 and 30 times body weight, respectively) compared to glass.
• Males generated higher attachment forces than females on both convex elytra (1.2x) and flat glass (6.8x).
• Convex substrates, like elytra, enhance beetle attachment due to favorable leg, tarsus, and seta angles.

Conclusions:

• Sexual dimorphism in tarsal setae contributes to differential attachment strengths in rosemary beetles.
• Elytra provide an advantageous substrate for attachment, enhancing the beetles' ability to maintain grip.
• The custom tribometer with a self-aligning holder is effective for studying attachment forces in living biological specimens.