Abstract
The mirid bug Apolygus lucorum Meyer-Dür, 1843, an omnivorous species that feeds on plants and animals, has become a major pest in China as production of Bt-cotton has grown to such a large scale. Its omnivory is likely to be critical for its success, but the digestive mechanism(s) underlying processing and adsorption of such diverse foods is relatively unknown. Here, we examined the activities of digestive enzymes of A. lucorum in the salivary gland complex and midgut and the effect of sex, age, and food source on these activities. Amylase and protease were present in the salivary gland complex and the midgut, but were higher in the salivary gland complex. Trypsin-like enzyme was also present in both organs, but chymotrypsin-like enzyme was present only in the midgut. Sex, age, and food source affected the activities of these digestive enzymes. In general, the activities of these enzymes peaked at 10 d after emergence, and amylase and protease activities were higher in female adults than in males. Of the food sources tested, green bean pods (Gb) induced the highest amylase activity, whereas Helicoverpa armigera Hübner, 1809 eggs (He) and a mixture of Gb and He induced higher activities of the trypsin-like and chymotrypsin-like enzymes. The results from food switching experiments confirmed that amylase activity could be induced by plant sources, and animal sources induced protease activity. Thus, the types and activities of digestive enzymes in A. lucorum provide the physiological basis of the pest’s omnivory.
Highlights
The mirid bug Apolygus lucorum Meyer-Dur, 1843, an omnivorous species that feeds on plants and animals, has become a major pest in China as production of Bt-cotton has grown to such a large scale
The nature of the food source, i.e., plant or animal, that an insect can assimilate is related to the type of digestive enzymes that the insect secretes into the salivary gland complex and the midgut of the insect, and the substrates used by these enzymes (Agusti and Cohen 2000, Torres and Boyd 2009)
Because the digestive enzymes in A. lucorum originate in the salivary gland complex rather than the midgut, and because enzyme activities were greater in female adults than in male adults, the salivary gland complex from female adults was used in experiments on different foods and on food switching
Summary
The mirid bug Apolygus lucorum Meyer-Dur, 1843, an omnivorous species that feeds on plants and animals, has become a major pest in China as production of Bt-cotton has grown to such a large scale. We examined the activities of digestive enzymes of A. lucorum in the salivary gland complex and midgut and the effect of sex, age, and food source on these activities. Of the food sources tested, green bean pods (Gb) induced the highest amylase activity, whereas Helicoverpa armigera Hubner, 1809 eggs (He) and a mixture of Gb and He induced higher activities of the trypsin-like and chymotrypsin-like enzymes. The nature of the food source, i.e., plant or animal, that an insect can assimilate is related to the type of digestive enzymes that the insect secretes into the salivary gland complex and the midgut of the insect, and the substrates used by these enzymes (Agusti and Cohen 2000, Torres and Boyd 2009). The results of this study demonstrate that the types of digestive enzymes and their activities confer the digestive adaptations for zoophagy and phytophagy in A. lucorum
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