Research

Surface structure, model and mechanism of an insect integument adapted to be damaged easily

Jean-Luc Boevé¹ , Véronique Ducarme^1,2 , Tanguy Mertens³ , Philippe Bouillard³ and Sergio Angeli^4,5

¹  Department of Entomology, IRSNB-KBIN, Royal Belgian Institute of Natural Sciences, Rue Vautier 29, B-1000 Bruxelles, Belgium

²  Present address: Unité d'écologie et de biogéographie, Croix du Sud, 4–5, B-1348 Louvain-la-Neuve, Belgium

³  Unité de modélisation des structures et des matériaux, CP 194/5, Université Libre de Bruxelles, Avenue Roosevelt 50, B-1050 Bruxelles, Belgium

⁴  Institut für Zoologie, Stephanstrasse 24, Justus-Liebig-Universität Giessen, D-35390 Giessen, Germany

⁵  Present address: Institut für Forstzoologie und Waldschutz, Georg-August Universität Göttingen, Büsgenweg 3, D-37077 Göttingen, Germany

author email corresponding author email

Journal of Nanobiotechnology 2004, 2:10doi:10.1186/1477-3155-2-10

Published:	1 October 2004

Abstract

Background

Several sawfly larvae of the Tenthredinidae (Hymenoptera) are called easy bleeders because their whole body integument, except the head capsule, disrupts very easily at a given spot, under a slight mechanical stress at this spot. The exuding haemolymph droplet acts as a feeding deterrent towards invertebrate predators. The present study aimed to describe the cuticle surface, to consider it from a mechanistic point of view, and to discuss potential consequences of the integument surface in the predator-prey relationships.

Results

The integument surface of sawfly larvae was investigated by light microscopy (LM) and scanning electron microscopy (SEM) which revealed that the cuticle of easy bleeders was densely covered by what we call "spider-like" microstructures. Such microstructures were not detected in non-easy bleeders. A model by finite elements of the cuticle layer was developed to get an insight into the potential function of the microstructures during easy bleeding. Cuticle parameters (i.e., size of the microstructures and thickness of the epi-versus procuticle) were measured on integument sections and used in the model. A shear force applied on the modelled cuticle surface led to higher stress values when microstructures were present, as compared to a plan surface. Furthermore, by measuring the diameter of a water droplet deposited on sawfly larvae, the integument of several sawfly species was determined as hydrophobic (e.g., more than Teflon^®), which was related to the sawfly larvae's ability to bleed easily.

Conclusion

Easy bleeders show spider-like microstructures on their cuticle surface. It is suggested that these microstructures may facilitate integument disruption as well as render the integument hydrophobic. This latter property would allow the exuding haemolymph to be maintained as a droplet at the integument surface.