A brief look at sexual dimorphism in the midgut morphology of lower Diptera and its implications for hematophagy

Abstract

The insect digestive system is divided into three sections: the foregut, the midgut, and the hindgut. Specific subdivisions and modifications in these regions can characterize distinct insect groups, representing apomorphies. Since only females of hematophagous insects from nematoceran Diptera feed on blood, nearly all studies have focused on specimens of this sex, often neglecting the studies on the males’ internal anatomy. In our studies of Lower Diptera (Nematocera) (Lutzomyia longipalpis Lutz & Neiva, 1912, Aedes aegypti Linnaeus, 1762, and Culex quinquefasciatus Say, 1823), we observed differences in midgut morphology between males and females. In hematophagous species, within both Culicomorpha and Psychodomorpha, females exhibit a prominent dilation in the posterior midgut. In contrast, in Culicomorpha males only a slight dilation in the posterior region of the midgut was observed. For Psychodomorpha males, the midgut remained tubular and narrow throughout its length. Interestingly, in the non-hematophagous insect Clogmia albipunctata Williston, 1893 (Diptera: Psychodidae) both males and females possess a tubular and narrow midgut. Our showed that the observed differences are related to hematophagy, where all hematophagous females have a midgut with prominent posterior dilation, while females from non-hematophagous species have a narrowed midgut. These observations, if further validated, could significantly impact future studies in insect physiology and evolutionary biology, inspiring new research directions and methodologies.