Superpropulsion of liquid droplets in sharpshooter insects

Sharpshooters are plant-sucking agricultural pests that constantly discharge large quantities of discrete water-based droplet excreta while feeding on plant’s xylem. Owing to a catapult-like mechanism powered by a biological spring located at their anal stylus, sharpshooters are able to blast away discrete droplet excrements at high accelerations reaching 200 m/s². Here, we unravel the propulsion mechanism exploited by sharpshooters that enables them to optimize the droplet ejection kinematics. Unlike the take-off speed of a rigid projectile that is set by maximum speed of the launching spring, we find that the elastic liquid droplets in sharpshooters can achieve take-off velocities that are up 3X faster than the underlying spring. This ‘superpropulsion’ behavior reveals that the frequency of the insect stylus is tightly tuned to the Rayleigh frequency of droplets (f₀~R^-3/2), providing insight into the physical limits on the maximum size and speed droplets in these extraordinary insects.