A developmental switch from capillary rectification to elastic catapult enables honeydew ejection in the spotted lanternfly

TL;DR

The paper reveals how the spotted lanternfly switches its honeydew ejection mechanism from capillary rectification in nymphs to elastic catapult in adults, adapting biomechanics across development to maintain waste clearance.

Contribution

It uncovers the ontogenetic transition in honeydew release mechanics, linking biomechanics to developmental stages in a plant sap-feeding insect.

Findings

Nymphs use a capillary rectifier with an anal stylus for droplet detachment.

Adults employ an elastic stylus with greater momentum for droplet ejection.

Both stages operate at low Weber and Bond numbers, but differ in droplet deformation regimes.

Abstract

Plant sap-feeding insects must dispose of excess fluid, yet at millimeter scales droplet release is constrained by capillary adhesion and contact-line pinning. How phloem-feeding insects solve this puzzle, particularly as the excretory apparatus changes in size and form from nymph to adult, has remained unclear. Combining micro-CT, high-speed imaging, measurements of honeydew properties, and reduced-order modeling, we show that the spotted lanternfly (Lycorma delicatula) uses distinct release mechanics across ontogeny. Nymphs release honeydew with an anal stylus that acts as a capillary rectifier, imposing a curvature asymmetry that biases the attached droplet toward detachment through a Laplace-pressure difference. Adults use a longer stylus associated with an elastic basal region, maintain stylus-droplet contact through a finite compression phase, and release droplets with greater translational and rotational momentum. In both stages, stylus rotation is ultrafast, with peak angular accelerations of order $10^7$ rad/s$^{-2}$ and release unfolding on millisecond timescales, yet droplet ejection speed remains below stylus tip speed. Weber-Bond scaling based on measured honeydew properties places both stages at $We_d<1$ and $Bo_d<1$ at the outlet, but distinguishes their post-release states: nymphal droplets remain surface-tension dominated, whereas adult droplets enter deformation- and spin-influenced regimes. Development therefore maintains waste clearance across ontogeny under the same outlet-scale capillary constraint by changing how stylus motion is coupled to the droplet at release, linking life-stage biomechanics to honeydew placement in this invasive phloem feeder and suggesting bioinspired strategies for droplet ejection, antifouling, and self-cleaning surfaces.