Microstructure, Nanostructure and Properties of the Wasp Petiole
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0975-DD07-04
Microstructure, Nanostructure and Properties of the Wasp Petiole Emily J. Reed1, Michael R. Dunlap2, Jacek Jasinski2, and Christopher Viney2 1 School of Natural Sciences, University of California at Merced, P.O. Box 2039, Merced, CA, 95344 2 School of Engineering, University of California at Merced, P.O. Box 2039, Merced, CA, 95344
ABSTRACT The wasp petiole (waist) is a self-assembled, multifunctional, hierarchically structured tube, which in some species has a simple, near-cylindrical shape that simplifies mechanical property characterization. We describe studies performed by scanning electron microscopy and transmission electron microscopy that reveal several details about the hierarchical structure of mud dauber wasp petiole, including: the number and thickness of the concentric layers of cuticle comprising the wall; the similarity (and differences) between the wall structure and the structure of multi-layer corrugated cardboard; and the different anisotropies of the dorsal and ventral internal surfaces. We also describe a simple experiment in which a petiole is used as a cantilever to determine its stiffness in bending; the result (1.5 GPa) demonstrates a material efficiency in bending similar to that of GFRP and aluminum. INTRODUCTION The petiole of a wasp is a narrow constriction occurring between the first and second abdominal segments. In the case of the mud dauber Sceliphron caementarium (Hymenoptera: Sphecidae) the petiole is approximately cylindrical; it can attain lengths exceeding 5 mm, while the external width is only ca. 0.5 mm. It is hollow ñ accommodating and protecting the alimentary canal, nerve tissue, an aorta, and open circulatory functions that communicate between the thorax and remaining abdominal segments. As well as being crush-resistant, fracture-resistant and puncture-resistant, the self-assembled cuticular material that constitutes the petiole wall must confer stiffness and resilience in bending, especially when the load on the petiole increases as the wasp uses its stinger to immobilize prey, and it must achieve all these properties without contributing unduly to the weight of the insect. Therefore, the petiole presents an intriguing model system from which to learn lessons about (i) the relationship between efficient use of material, molecular organization, and mechanical property optimization in the context of a simple object geometry, and (ii) the factors that limit molecular and energy transport when such an object is self-assembled. Here we present some initial findings relevant to the first of these lessons.
STRUCTURAL CHARACTERIZATION Sample preparation Specimens for structural characterization were harvested from wasps that had been allowed to air dry for a month or longer. For SEM, the petiole was dissected from the wasp and mounted in paraffin wax for support. A sharp razor blade was used to section the encased petiole transversely in two locations, and the middle piece was then sectioned longitudinally. The wax was dissolved with an organic solvent (chlorofor
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