How aphids lose their marbles

Abstract

Insects provide examples of many cunning stratagems to cope with the challenges of living in a world dominated by surface forces. Despite being the current masters of the land environment, they are at constant risk of being entrapped in liquids, which they prevent by having waxy and hairy surfaces. The problem is particularly acute in an enclosed space, such as a plant gall. Using secreted wax to ef ciently parcel and transport their own excrement, aphids were able to solve this problem 200 Myr ago. Here, we report on the physical and physiological signi cance of this ingenious solution. The secreted powdery wax has three distinct roles: (i) it is hydrophobic, (ii) it creates a microscopically rough inner gall surface made of weakly compacted wax needles making the gall ultra-hydrophobic, and (iii) it coats the honeydew droplets converting them into liquid marbles, that can be rapidly and ef ciently moved.

Brochosomes protect leafhoppers (Insecta, Hemiptera, Cicadellidae) from sticky exudates

“…This observation is not at odds with the superhydrophobic properties of the brochosomal powder. If their adhesion to the solid surface is sufficiently weak, even hydrophobic particles adhere to aqueous droplets, producing the well-known Lotus effect [7] and causing chunks of hydrophobic wax to coat exudate droplets of some gall-inhabiting aphids [8]. In our experiment, impacting droplets removed only small amounts of the brochosomal powder ( figure 4c,d), leaving no bald spots in the coats ( figure 4a,b).…”

“…Forceful shooting of exudates away from the body is widespread, but it does not protect either from discharges of other individuals or from getting stuck to contaminated plant surfaces. Some galling aphids (Hemiptera, Aphidoidea) escape entrapment by the honeydew inside the narrow space of their galls by coating their exudate droplets with loose superhydrophobic wax powder [8]. Particulate waxes secreted by integuments of free-living aphids and other sap-sucking hemipterans display intricate structure at the submicron level [10][11][12][13][14][15], which probably (direct measurements are absent) makes them water repellent, similar to better studied cuticular waxes of plants [7].…”

Brochosomal coats turn leafhopper (Insecta, Hemiptera, Cicadellidae) integument to superhydrophobic state

“…However, those of xylem-feeding leafhoppers (such as C. viridis) are close in composition to pure water [54,55], and those of phloem-feeding species (such as A. argentarius) contain excess sugars and are expected to be similar to honeydew of other phloem-sucking hemipterans, such as aphids. Using the capillary method, Pike et al [56] estimated the surface tension of honeydew produced by the aphid Pemphigus spirothecae as 50 mN m 21 . In this study, two liquids with the surface tension of 48 and 50 mN m…”

Dynamics of Surfactant-Driven Fracture of Particle Rafts

“…For instance, liquid drops coated with a fine hydrophobic powder become non-wetting [1], forming an artificial analog of a much older solution stumbled upon by insects [2]. Similarly, the addition of particles to the surface of liquid drops prior to coalescence stabilises the coalesced drops to the common pinch-off instability and can lead to reversible morphological instabilities such as buckling when subject to pressure Recent experiments [7,8] show that a densely packed monolayer of particles at an interface (a 'particle raft') has many of the characteristics of a two-dimensional linear elastic solid in certain regimes.…”