Expanding abdominal cuticle in the bug Rhodnius and the tick Boophilus.

Abstract The abdominal cuticles of Rhodnius prolixus (fifth instar) and Boophilus microplus (adult female) expand dramatically and rapidly during feeding. In the unfed stage of both species the epicuticle of the abdomen is deeply folded, and when rapid stretching takes place the epicuticle unfolds and the underlying procuticle stretches so that the thickness of the cuticle is halved. The cuticles contained only trace amounts of protein soluble in water and aqueous KCl but substantial quantities were extracted with 7 M aqueous urea. The proteins were analysed for their amino acid composition and investigated by gel electrophoresis and isoelectric focusing. In solubility, amino acid composition, molecular weight distribution, and isoelectric points, the proteins isolated from both species resembled one another closely. They had higher molecular weights and higher isoelectric points than did the proteins from flexible, non-stretching cuticles and unlike them had high alanine and histidine and low aspartic acid and glutamic acid contents. Their amino acid composition was very similar to that of the whole cuticle. The proteins were not associated with neutral sugars. Both the Rhodnius and Boophilus cuticles had low chitin contents, 11·2 and 3·8% respectively (on a water-free basis). The composition of the cuticles and the properties of the proteins are discussed in relation to the stretching which they undergo.