The role of speed secret in the exchange ratio between animal and food plant in homopters and heteropters | Die Rolle der speichelsekrete im wechselverhältnis zwischen tier und nahrungspflanze bei homopteren und heteropteren

The above article is a short survey of the relation between the salivary secretions of the Hemiptera and their host plants. In analyses of the composition secretions in the salivary glands of phytophagous Homoptera and Heteroptera, the most extensive work has been done on the digestive enzymes. Proteases, amylases, saccharase, maltase, pectinase and lipase have been detected, but most commonly only 2-3 of these occurs in any one species. An adaptation of the enzyme complement to the diet is evident and in this respect the feeding site used by the insect is especially decisive to the enzyme composition of the saliva. Proteases and amylases occur in the saliva of mesophyll feeders, but are absent in phloem feeders, for which they are useless because, from the insect's point of view, the food is already digested. The adaptation of the salivary enzymes to the nature of the food seems to be largely inherited, for a diet containing nothing but sucrose does not induce adaptive changes in the enzyme content of the salivary glands. By contrast, papain seems to be transferred from a synthetic food to the salivary glands. The disease symptoms caused in plants by the salivary toxins of Homoptera and Heteroptera have many similarities to those caused by abnormal amounts of growth hormones. Indole-tri-acetic acid has been detected in extracts of crushed aphids and leafhoppers, although no growth stimulating hormones have been detected in salivary glands dissected from several heteropterous bugs and one aphid. On the contrary, substances inhibiting plant growth exist in the salivary glands of many Heteroptera and in at least one aphid. In some experiments with a heteropterous bug, indole-tri-acetic was observed to have been transferred from a synthetic diet to the salivary glands. It seems possible that auxins, enzymes and other phytotoxic substances occurring in the salivary glands of insects may at last in some cases originate from the host plant and are not produced by the insect. The salivary enzymes without doubt play an important role in the digestion of the insects secreting them. They are important also in the differentation of Homoptera and Heteroptera to different modes of life. The auxins or auxin inhibitors, as wel as all phytotoxic substances in the salivary glands of Homoptera and Heteroptera are significant for these animals by changing the physiological state of the host plant in such a direction that its suitability as a source of food increases.