The anatomy of the head and mouth parts of Psylla mali, the Apple sucker, with some remarks on the function of the labium

Abstract

The investigation, of which the results contained in this paper are a part, was first commenced in 1910. It was then proposed to describe in some detail the entire anatomy of the adult insect, but when a measure of progress had been made, and the alimentary, tracheal, and nervous systems had been almost completed, the work was interrupted by my taking up an appointment in India. On returning to England in 1915, the enquiry was resumed for a short period at the end of the year, but early in 1916 it had to be abandoned again to meet the superior claims of entomological work with the Forces in Mesopotamia, for the War Office. This, and other investigations connected with problems which have arisen in England in consequence of the War, prevented any further progress being made, but, with the declaration of the Armistice it was felt that attention might once more be given to it. In the limited time which could be devoted to the work, it has not been possible to carry out the original plan of including the whole anatomy in one paper, and the description of the head and mouth parts has been selected because of the somewhat novel considerations which have arisen in connection with the latter, particularly with regard to the function of the labium during the operation of piercing, the publication of which it seemed undesirable to delav further.

Directional control of the stylets in phytophagous Hemiptera

“…The maxillary stylets of Trialeurodes vaporariorum (Westwood) are fused (Hargreaves, 1915), those of Eriosoma Ianigerum (Hausmann) are not fused but towards their extremities appear to be so (Davidson, 1914), and a similar condition exists (Grove, 1919) in Psylla mali Schmidberger. Such united stylets, unlike the separate mandibulars, will not move independently-a condition also suggested for Aphis fabae Scopoli by Davidson (1923)-and a force applied to the base of one will cause curvature of both.…”

“…It is essential for penetration (Pesson,1944), and particularly for bending, that the maxillary and mandibular stylets interlock. If they do not, as for example in P. mali (Grove, 1919), then either they must be held together by surface tension forces (Wigglesworth, 1966) or the mandibular stylets must be modified in structure and behaviour to prevent them separating from the paired maxillaries. This can be achieved by increasing their size and stiffness, as in large predaceous Heteroptera, or by restricting their entry into plant tissue, as in Eupterys melissae.…”

The stylet structure of a leafhopper (Eupteryx melissaeCurtis: Homoptera, Cicadellidae)

“…The axial cavities do not open distally (Geise, 1883 ;Grove, 1919 ;van Hoof, 1958 ;Pesson, 1951) and this appears to be true of Eupteryx melissae. On the other hand, they have been claimed to communicate with the haemocoele (Awati & Wolfe-Barry, 1914 ;Frazer, 1944 ;Pinet, 1963) and contain haemolymph (Parrish, 1967), a condition which also holds for the leafhopper.…”

The mechanism of stylet movement in Psylla mali Schmidberger (Homoptera: Psyllidae)

“…The morphology of the head of PsylEa mali has been described by Grove (1919) and Weber (1929) while Brocher (1925) illustrated some of the stylet movements of P.pyrhga Forster nymphs. Two general drawings (Figs.…”

“…Labial propulsion has been explained by assuming that the apex (Grove, 1919) or the clamp (Brocher, 1925) can grip and move the bundle. Interaction between the labrum and labium has been invoked (Heriot, 1934) whilst movements of the crumena have also been suggested (see Snodgrass, 1935 ;Pesson, 1944).…”