The hind wing of the desert locust (Schistocerca gregaria Forskål). II. Mechanical properties and functioning of the membrane.

As part of an investigation of the functional mechanics of the hind wing of the desert locust Schistocerca gregaria, the Young's modulus of the membrane was measured using a newly developed universal materials test machine capable of testing very small specimens of cuticle, down to 1 mm gauge length. Strain was measured optically. Specimens were cut from various locations around the wing and tested under controlled temperature and humidity. The modulus of the membrane was typically between 1 and 5 GPa, but both this and the membrane thickness varied around the wing, with the remigium and the anal fan showing markedly different properties. The membrane was tested for chitin using two methods: a gas pyrolysis/mass spectrometry assay, and a gold-labelled immunoassay specific to chitin. None was detected, and the membrane may consist of epicuticle alone. The wings were examined for evidence of crystalline material using standard polarising microscopy and an advanced technique that distinguishes between three components of the polarised image. Birefringence was detected in the membrane of the anterior part of the wing, but vanished when the membrane was separated from the surrounding veins, suggesting that it was due to pre-stress rather than to ultrastructure. The implications are discussed.