Estudo da fisiologia da glândula salivar e do intestino de larvas de terceiro estádio e adultos de Chrysomya megacephala (Fabricius, 1794)

Abstract

The Chrysomya megacephala fly (Fabricius, 1794) has a close relationship with humans and animals, for acting as an important potential disseminator of pathogens and for causing myiasis. Its larvae are necrobiontophagous and the adults feed on nutrient suspensions and bacteria, with the gut being the place for processing the diet. The pH and biological activities present in the intestine are factors that interfere directly in the digestive process and, consequently, in the development and survival of individuals. Thus, the aim of this study was to study the physiology of the salivary gland and intestine of third instar larvae and adults of C. megachephala. The specimen mass was measured daily on an analytical balance. To assess the intestinal flow, the larvae were fed with macerated fish meat homogenized with powdered activated charcoal. The amount of proteins per salivary gland pair of third instar larvae was evaluated by the protein dosage method described by Bradford (1974). To assess the intestinal pH, different pH indicator dyes were used. The activity of endoproteinase in the intestine was evaluated by decomposition of the substrate azoalbumin. The catalase activity in the intestine was measured by the rate of decomposition of hydrogen peroxide in the presence of the intestine extract and the lysozyme activity was measured by the lysis of the bacterium Micrococcus lysodeikticus. The results showed that the mass gain was extremely fast in the first three days of larval development and in four days the larvae increased from 0.3 mg to 42.5 mg. Three-day-old third-instar larvae presented the length of the salivary glands with differences in length (p<0.01) and in the amount of proteins (p<0.001). The mean time that the food ingested by the larvae took to be excreted was 48.8 ± 6.2 minutes. In larvae, the middle midgut region had the most acidic pH (between 4.0 and 6.5) when compared to the other regions that had pH ranging from 4.5 to 7.0. In adults, the pH inside all evaluated regions of the intestine was acidic (between 5.5 and 6.5). The activity of endoproteases in the intestine was higher in larvae at pH 7.5 and 8.0 and in adults, regardless of the pH tested, the activity was lower. Larvae and adults have lysozyme activity in the intestine, which is more than twice as high in larvae. The larvae had an average activity of catalase in the intestine of 400 μmol/min while the adults had an average activity approximately 22 times lower (18 μmol/min; p<0.05). The parts of the intestine of larvae with the highest catalase activity were the IMM with 94.0 μmol/min. While in adults were the regions of the IMM and IMP, both with 4.5 μmoles/min. All the different regions of the intestine of the larvae presented catalase activity higher than those verified for the adults. The results obtained in this study demonstrate the need to further study the role of the salivary gland and the intestine of the L3 of C. megacephala to understand how the digestion of proteins, lipids and carbohydrates occurs which bacteria colonize the intestine, the role of the products of secretion and excretion in digestion, development and in the innate immune response.