Insects had it first: surfactants as a defence against predators

Abstract

Insects have evolved an astonishing array of defences to ward off enemies. Well known and widespread is the regurgitation of oral secretion (OS), fluid that repels attacking predators. In herbivores, the effectiveness of OS has been ascribed so far to the presence of deterrent secondary metabolites sequestered from the host plant. This notion implies, however, that generalists experience less protection on plants with low amounts of secondary metabolites or with compounds ineffective against potential enemies. Resolving the dilemma, we describe a novel defence mechanism that is independent of deterrents as it relies on the intrinsic detergent properties of the OS. The OS of Spodoptera exigua (and other species) was found to be highly amphiphilic and well capable of wetting the hydrophobic cuticle of predatory ants. As a result, affected ants stopped attacking and engaged in extensive cleansing. The presence of surfactants was sufficient to explain the defensive character of herbivore OS. We hypothesize that detergency is a common but unrecognized mode of defence, which provides a base level of protection that may or may not be further enhanced by plant-derived deterrents. Our study also proves that insects 'invented' the use of defensive surfactants long before modern agriculture had started applying them as insecticides.

Social Transfer of Pathogenic Fungus Promotes Active Immunisation in Ant Colonies

“…Upregulation of grooming frequency not only against individuals treated with infectious material but also with sham control solutions is known from previous studies [29],[51] and indicates that ants are very sensitive to applications on the bodies of their group members.…”

Building a home from foam—túngara frog foam nest architecture and three-phase construction process

“…In relation to this, we have noticed that, during initiation of communal nestings, the male of one pair will issue a call that induces an encroaching pair to move away (M. W. Kennedy 2002Kennedy , 2004Kennedy , 2008. Lastly, a cortex would reduce access to the eggs by predators or parasites, which would be given added effect by surfactants in the foam as anti-insect defence (Rostás & Blassmann 2009).…”

Biosurfactants in agriculture

“…The synthetic surfactant presently used in pesticides industries act as emulsifying, dispersing, spreading and wetting agent and enhance the efficiency of pesticides. In addition, these surfactants are used in insecticides in modern agriculture as these have defensive properties (Rostas and Blassmann 2009). Different types of surfactants such as anionic, cationic, amphoteric, and nonionic are presently being used at several pesticide manufacturing industries (Mulqueen 2003).…”