Thiamethoxam is a neonicotinoid that has been used to control insect pests. The literature reports a few behavioral studies evaluating the toxic effect of thiamethoxam in ants; however, there are scarce studies at the cellular level. The present research evaluated the effects of thiamethoxam in labial (LG) and mandibular glands (MG), fat bodies (FB), and Malpighian tubules (MT) of workers of Atta sexdens, using transmission electron microscopy. The duct and secretory cells of LG were profoundly affected, then the production of saliva can be compromised, as well as its quality and subsequent use. In MG, reservoir and canaliculi cells presented slight alterations; however, MG secretory cells presented vacuoles containing lamellar structures, increased lipid production, and a large amount of mitochondria, which may lead to organ's malfunctioning. The FB cell alterations do not seem enough to cause significant changes that lead to cell death. Prominent changes in MT, such as loss of the electron-dense concentric ring, increased smooth endoplasmic reticulum, loss of basal infolds, vacuoles containing mineralized granules, and lamellar structures associated with mitochondria, suggest that their excretory function is compromised. In conclusion, thiamethoxam acts not only in the nervous system but also contributes to systemic toxicity on the target organism.

Bumblebees need to keep bodily homeostasis and for that have an efficient system of excretion formed by the Malpighian tubules, ileum, and rectum. We analyzed the excretory organs of Bombus morio, a bee without rectal pads. In addition, we analyzed the rectal epithelium of Melipona quadrifasciata anthidioides which has rectal pads. The Malpighian tubules exhibited two cell types and the ileum four types. However, comparative analysis of the rectum showed that only cells of the anterior region of the rectal epithelium of B. morio are structurally distinct. We suggest that cells of the Malpighian tubules of B. morio have an excretory feature and that cells of ileum have different functions, such as ion absorption and water, organic compound, and protein secretion. In addition, only the anterior region of the rectum of B. morio showed characteristic absorption. We suggest that Malpighian tubules participate in the excretion of solutes and that the ileum and rectal epithelium are responsible for homeostasis of water and solutes, compensating for the absence of rectal papillae. These results contribute to our understanding of the morphophysiology of the excretory organs of bees without rectal pads.

The larval Malpighian tubules of Sarcophaga ruficornis Fab. consist of two types of cells, namely principal and stellate cells. The principal cells are characterized by a large euchromatic nucleus, well-developed basal plasma membrane infoldings associated with mitochondria and prominent luminal microvilli containing mitochondria with well-developed cristae. The central cytoplasm of the cells contains clear vacuoles, lysosomes, mineral concretions or spherocrystals, lipid droplets and peroxisomes. The stellate cells are thin with extremely short basal plasma membrane infoldings and luminal microvilli devoid of mitochondria. The ultrastructural features of the principal cells show the characteristic of transporting cells engaged in water and ion transport. The cells are separated by septate junctions. The tubules are richly supplied by the tracheae.

The stable fly, Stomoxys calcitrans L., has two pairs of Malpighian tubules. Ultrastructurally, the tubules consist of three morphologically distinct zones: the distal, intermediate and proximal regions, which themselves are characterized by distinct cell types. The tubule cells have numerous mitochondria, microvilli and basal infoldings, which are associated with mitochondria. It is suggested that the distal and intermediate regions are secretory, while the proximal region is reabsorptive; and that the haemotophagous habit in S. calcitrans is probably correlated with the ultrastructure of its Malpighian tubules.

The tsetse, Glossina morsitans morsitans, has two pairs of Malpighian tubules. Ultrastructurally, the tubules consist of three recognizable functional zones: the distal, intermediate and proximal regions, which are characterized by three distinct cell types: I, II and III respectively. The three cell types had numerous microvilli and basal infoldings: the microvilli of type I and II cells were associated with long mitochondria, while those of type III were devoid of mitochondria. Autoradiographic observations using (3H) glucose indicated that there was synthetic activity in the tubules, and that there was greater incorporation of the radiochemical in the distal and intermediate tubule regions than in the proximal region. The distal and intermediate regions have some functional similarities. With regard to primary urine formation in the tubules, it is suggested that the cell types I and II (and hence the distal and intermediate regions) are secretory, and the cell type III (that is, the proximal region) is absorptive. “Canaliculi” in the proximal region increase the surface area for absorption.

Sandflies caught from termitaria at Tseikuru (Kitui District) and Masinga (Machakos District) were dissected and examined for the presence of Leishmania. Leishmanial parasites were found in the guts of 12 out of 112 Sergentomyia garnhami from Tseikuru and in 2 out of 48 S. antennatus from Masinga. Five of the 12 S. garnhami and 1 of the 2 S. antennatus had leishmanial parasites in the malpighian tubules. Electron microscopic investigations revealed that in the malpighian tubules of S. garnhami the parasites were either free in the lumen or in close contact with the basement membrane.