The spined soldier bug, Podisus maculiventris, is a generalist predator of insects and has been used in
biological control. However, information on the digestion of food in this insect is lacking. Therefore, we have studied the digestive system in P. maculiventris, and further characterized carbohydrases in the digestive tract. The midgut of all developmental stages was composed of anterior, median, and posterior regions. The volumes of the anterior midgut decreased and the median midgut increased in older instars and adults, suggesting a more important role of the median midgut in food digestion. However,
carbohydrase activities were predominant in the anterior midgut. In comparing the specific activity of carbohydrases, α-
amylase activity was more in the salivary glands (with two distinct activity bands in zymograms), and
glucosidase and
galactosidase activities were more in the midgut. Salivary α-
amylases were detected in the prey hemolymph, demonstrating the role of these
enzymes in extra-oral digestion. However, the catalytic efficiency of midgut α-
amylase activity was approximately twofold more than that of the salivary gland
enzymes, and was more efficient in digesting soluble
starch than
glycogen. Midgut α-
amylases were developmentally regulated, as one
isoform was found in first instar compared to three
isoforms in fifth instar nymphs.
Starvation significantly affected
carbohydrase activities in the midgut, and
acarbose inhibited α-
amylases from both the salivary glands and midgut in vitro and in vivo. The structural diversity and developmental regulation of carbohydrases in the digestive system of P. maculiventris demonstrate the importance of these
enzymes in extra-oral and intra-tract digestion, and may explain the capability of the hemipteran to utilize diverse food sources.