Ultrastructural observation of digestive tract and the adaptative characteristics of dietary habits for ground-dwelling and omnivorous insects

Abstract

The digestive tract of insects from mouth to anus is the crop, proventriculus, gastric caecum, midgut, ileum, colon and rectum, and the Malpighian tubules attached to the ileum belong to the excretory organs. As the main organs for digesting food and absorbing nutrients, the structure of the insect digestive tract is inevitably adapted to feeding habits. Among the Orthoptera, the digestive tracts of phytophagous locusts and carnivorous katydids have been studied for their adaptations to their food habits, while the adaptations of the digestive tracts of omnivorous insects have been less studied. In order to systematically study the adaptations of the digestive tracts of ground-nesting omnivorous insects to their feeding habits, this study was carried out with Loxoblemmus taicoun Saussure, 1877, Teleogryllus emma (Ohmachi & Matsuura, 1951), and Velarifictorus micado (Saussure, 1877). Through the use of a scanning electron microscope (SEM) and a VHX digital microscope, the digestive tract structures of these three most widespread and common omnivorous crickets in China were examined in order to better understand how omnivorous insects’ digestive tract structures differ from those of specialists. When we compared the morphological features of these crickets’ digestive tracts to those of phytophagous and carnivorous insects, we discovered six adaptive traits of omnivorous insects, including: (1) they have a shorter foregut and longer midgut and hindgut; (2) they have a well-developed muscular intestinal wall; (3) the spines in the inner wall of their crop are uniformly arranged and less chitinized; (4) the proventriculus is sclerotized and spherical, and the inner wall is accompanied by ossified large teeth; (5) they have well-developed cilia at the base of the crop and at the base of the ossified denticles; (6) they have only two lobulated gastric caeca. The study summarizes six characteristics of the digestive tract of omnivorous crickets that are compatible with their food habits, providing evidence and clues for further research on the relationship between the digestive tract and food habits in Orthoptera.