Abstract
The stylet sheaths of the species tested show evidence of disulphide bonds as well as hydrogen bonds, contain some free sulphydryl groups, and are secreted with a polyphenol oxidase. They can be formed in solutions containing cyanide, ascorbate, or urea, but apparently not in solutions containing both cyanide and urea. It is suggested that the polyphenol oxidase serves to promote bonding within the body of the precursor of the sheath material, and that urea permits the cyanide to penetrate the precursor and inhibit the oxidase sufficiently rapidly to prevent sheath formation. A method for observing and testing some properties of the watery saliva of individual aphids is described. In the four species tested, the watery saliva has a pH of about 8, in contrast to the pH of the stylet sheath of about 6. In two species examined, the ‘main’ salivary glands are the chief sources of polyphenol oxidase and sulphydryl groups in the head capsule, and must be considered as the source of the sheath precursor. It is concluded that the physiology of formation of the stylet sheath is similar in aphids and the Heteroptera: Pentatomorpha.
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