Cibarial Pump Research Articles

V.—A Comparative Account of the Feeding Methods of the BeetlesNebria brevicollis(F.) (Carabidæ) andPhilonthus decorus(Grav.) (Staphylinidæ)

SynopsisNebria brevicollis(F.) andPhilonthus decorus(Grav.) are two of the commonest predaceous insects of the woodland floor, and the head structure, mouthparts and feeding methods of each have been compared and contrasted. InN. brevicollis, the mandibles are well developed for the capture and shearing of the prey, whilst the laciniæ of the maxillæ form rakes which pull the food towards the cibarium across the smooth labium. Food is bolted in large pieces and stored in the crop before passing through the filtering and grinding gizzard. A fundamental difference between the two beetles is seen in the movements and structure of the maxillæ, and a mechanism whereby stipital abduction and protraction is effected inN. brevicollishas been proposed. InP. decorus, the mandibles are also developed for prey capture but hold the prey between large brushes while it is being crushed. The maxillæ form thick brushes which also hold the prey, and the labium-hypopharynx is densely covered with setæ which prevent the entry of solid food into the mouth. Thus, in contrast toN. brevicollis, the labrum has a median food groove which directs the food upwards and away from the mouth, and returns it to the mandibles to be re-chewed. Here, partial external digestion occurs and fluid food is sucked in by the powerful cibarial pump, and passed to the filtering proventriculus. In order to show how the two feeding methods described fit into the general pattern, the feeding methods of various predaceous Coleoptera have been reviewed in relation to different types of gut structure.

Feeding Mechanism of Water-bugs

An account has been given by H. D. Slack of the cibarial suction pump of Corixidae, in which a modification producing the effect of chitinous jaws was noted1. A full account of the head and mouth parts of Rhamphocorixa acuminata has been previously given by M. E. Griffith2. Further, H. B. Hungerford3 has found solid food in the alimentary canal of Corixidae, in particular, jaws of rotifers, filaments of Oscillatoria sp. and Mougeotia sp., slime diatoms, etc. In an investigation begun in 1943, I have confirmed much of this work, and, in addition, have found legs of Crustacea, Anabaena sp., undamaged filaments of Spirogyra sp., an unexploded nematocyst, pollen grains, etc. I have also made observations on the feeding of Sigara striata, S. falleni, Corixa punctata and C. panzeri, on chironomid larvae, Mayfly nymphs and daphnids. In all cases the live food was pierced and anchored by the mouth parts, probably by the mandibular teeth described by M. E. Griffith2. The food thus seized was held for periods varying from five to twenty minutes, during which time some of the contents of the living animal were sucked into the corixid. On one occasion black pigment from the eye of a daphnid was observed streaming through the pharynx.

Feeding Mechanism of Water-Bugs

THE suggestion put forward by Walton1 that the presence of small teeth and chitinous elevations in the pharynx of Micronecta indicates that this Hemipteran ingests and masticates particulate food material appears to be true for other families of the Cryptocerata. There exists in many, and probably all, species of Corixidae a type of feeding mechanism which does not seem to have been recorded. This takes the form of a modification of the cibarial suction pump2 in such a manner as to produce a pair of chitinous jaws having a structure and position strongly suggesting that they function as organs for the comminution of solid material. It is a mechanism more elaborate in form than that found in Micronecta. The whole ventral wall of the cibarial pump consists of a curved chitinous plate having a thickened posterior margin. The anterior border of this plate appears to be folded back and modified into a transverse triangular bar set with rows of minute tooth-like projections. Above this bar and articulating with it at its lateral ends lies a second chitinous bar formed by the thickened dorsal wall of the cibarium and similarly equipped with teeth or rugosities (Fig.1). The two bars have the appearance of a pair of grinding jaws, and although the musculature of the organ has not been studied in detail, enough has been noted to support this supposition.