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.

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Abstract:Podisus maculiventris (Say) is a generalist predator attacking many insect species from different orders. The bug injects saliva into its prey's body. The ingested hemolymph and liquefied internal tissues pass through the bug's alimentary tract. Collagenase working on peptide bonds of collagen and basement membrane proteins, leads to the disintegration of the prey's internal organs.As yet, there is an almost complete lack of knowledge on the collagenase activity in P. maculiventris. The collagenase activity of the salivary glands and midgut was optimum at pH 8.0 which was congruent with the optimal pH of the total proteolytic activity of the salivary glands. More collagenolytic activity was determined in the posterior lobe of the salivary glands and anterior midgut. Significant inhibition of collagenolytic activity by ethylenediaminetetraacetic acid (EDTA) revealed the enzyme is a metalloproteinase. The collagenase activity notably decreased when the bug went hungry. The salivary gland collagenase is a vital enzyme in extra-oral digestion and facilitates the action of other digestive enzymes. The midgut collagenase may be involved in the digestion of the ingested muscle fibers. The collagenase probably acts as an intoxicating agent in the saliva (venom) of P. maculiventris. Paralysing toxins are present in the salivary gland secretion.

Habrobracon hebetor Say (Hymenoptera: Braconidae) is a cosmopolitan idiobiont ectoparasitoid wasp and one of the most important biological control agents of lepidopteran larvae, especially of larvae of the family Pyralidae such as Indian meal moth, Plodia interpunctella (H€ ubner). Using biological control agents in combination with other pest management approaches may enhance the efficiency of pest management. Acarbose, a non-proteinaceous inhibitor, is well known for its inhibitory effect on insect digestive carbohydrases, especially a-amylase. In the present study the effect of the inhibitor on various physiological and biological parameters of the parasitoid H. hebetor was investigated in a diet-host-parasitoid tritrophic system. The inhibitor decreased a-amylase activity in both in vitro and in vivo assays with the parasitoid; however, there was no significant impact on the biological characteristics studied. Quantification of energy reserves in host larvae and adult parasitoids revealed a dose-dependent effect of the inhibitor on total protein, lipid, carbohydrate, and glycogen contents of the larval host, whereas total protein and carbohydrate of the parasitoid were only reduced at high inhibitor concentrations. In general, the inhibitor acarbose can interfere with some physiological processes in H. hebetor, although the parasitoid's fitness is not negatively affected. Therefore, enzyme inhibitors may be considered an effective tool for pest control in integrated pest management programs.