Abstract
In most mosquito species, the females require a blood-feeding for complete egg development. However, in Toxorhynchites mosquitoes, the eggs develop without blood-feeding, and both females and males exclusively feed on sugary diets. The midgut is a well-understood organ in blood-feeding mosquitoes, but little is known about it in non-blood-feeding ones. In the present study, the detailed morphology of the midgut of Toxorhynchites theobaldi were investigated using histochemical and ultrastructural methods. The midgut of female and male T. theobaldi adults consists of a long, slender anterior midgut (AMG), and a short, dilated posterior midgut (PMG). The AMG is subdivided into AMG1 (short, with folds) and AMG2 (long, without folds). Nerve branches and enteroendocrine cells are present in AMG and PMG, respectively. Compared with the PMG of blood-feeding female mosquitoes, the PMG of T. theobaldi is smaller; however, in both mosquitoes, PMG seems be the main region of food digestion and absorption, and protein secretion. The epithelial folds present in the AMG of T. theobaldi have not been reported in other mosquitoes; however, the midgut muscle organization and endocrine control of the digestion process are conserved in both T. theobaldi and blood-feeding mosquitoes.
Highlights
In most mosquito species, the females require a blood-feeding for complete egg development
The midguts of both female and male T. theobaldi consist of a long, slender anterior midgut (AMG), and a smaller, dilated posterior midgut (PMG)
In both females and males, the AMG is divided into two distinct parts: AMG1, with folds on the surface and located in the thorax; and AMG2, without folds and located in abdomen
Summary
The females require a blood-feeding for complete egg development. The midgut has two portions, which differ morphologically and functionally: the anterior midgut (AMG) is mainly associated with sugar digestion and absorption[11,12]; and the posterior midgut (PMG), which is an expandable sac whose cells are involved in blood digestion (females exclusively), water regulation, digestive enzyme and peritrophic matrix (PM) component synthesis and secretion, and nutrient absorption[9,13,14]. The midgut in blood-feeding female mosquitoes is the site of blood digestion and the gateway for establishment of various human pathogen, including viruses, protozoa, and nematodes[17,18,19]. In the present study, the midgut morphological and functional characteristics of female and male Toxorhynchites theobaldi were investigated, and the differences between this species and blood-feeding mosquito species were discussed. This study will help in understanding the overall morphophysiology of the Culicidae midgut
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