LOW-VACUUM ELECTRON-MICROSCOPY OF CARABID CHEMORECEPTORS - A NEW TOOLFOR THE IDENTIFICATION OF LIVE AND VALUABLE MUSEUM SPECIMENS

High-vacuum scanning electron microscopy, following coating of specime ns with gold, produces high quality images that have proved invaluable for the study of insect sensilla. Unfortunately, the technique is ess entially destructive, and cannot be used on live or valuable museum sp ecimens. In particular, high-vacuum scanning usually causes the collap se of the tips of the palps, interfering with any examination of the s ensilla in this area. A new low-vacuum technique is described that avo ids these problems. Insect cuticle does not need to be coated with gol d, thus avoiding damage to important specimens. Examples are given of scans of the palp tips of live carabid beetles, anaesthetised with CO2 . It was shown that the technique could consistently display these tip s in their natural convex state. In all, four types of sensilla were i dentified by low-vacuum scans of the maxillary palps, and four further types on the terminal segment of the antennae, plus glandular opening s. The antennae revealed a type of sensilla that has not previously be en described on carabids. These sensilla showed clear structural diffe rences between the two species studied, Pterostichus melanarius Illige r and P. niger Schaller (Coleoptera: Carabidae), as a diagnostic chara cter for both fresh and dried specimens. The low-vacuum technique can be recommended for examining valuable 'type' specimens without risk of damage.