Pathways of Insect Protein Digestion: Triatominae (Kissing Bugs)

The majority of insects use serine proteinases like trypsin and chymotrypsin as main enzymes to digest their food [1]. These types of peptidases develop their maximum activity under alkaline to neutral pH conditions [2]. In some insect groups the intestinal lumen is acidic and the digestion switched to cysteine-like proteinases such as cathepsin D or L [3,4]. Some Coleoptera groups (e.g. Bruchidae, Tenebrionidae) developed a digestive system based on such proteinases [2,5]. But the major group using acid proteinases are the Hemiptera. This taxon uses cysteine proteinases because ancestral groups were using plant seeds containing serine proteinases inhibitors as a food source and therefore had to evolve their digestive system [6,7]. The conquest of this food source was a challenge for the digestive system [8] but it certainly contributed to the success of this insect group opening up new niches.