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METAZOAN PHYLA 



genetic female generations occur during the summer. In the fall males 

 are produced and fertilized eggs are laid which hatch out in the spring, 

 starting the first of another series of parthenogenetic female generations. 

 Most plant lice (Fig. 193) are wingless, though there are winged females. 

 They are often very injurious to plants, puncturing the leaf or stem and 

 sucking the sap. Many of these excrete a sweet substance known as 

 honeydew which is eaten by ants and other insects. The bodies of others 

 are covered with a white, cotton-like substance, also an excretion. 



In the order Homoptera belong also the cicadas or harvest flies. 

 Among these are the longest-lived of insects, the seventeen-year cicada 

 living as a nymph for seventeen years before emerging as an adult. 

 These insects lay their eggs in slits made by the female in the twigs of 



Fig. 194. — Work of an engraver, or scolytid, beetle, in a box elder limb. The female 

 beetle bores through the bark and then makes tunnels between the bark and wood. She 

 deposits eggs from time to time and the larvae hatched from them begin lateral tunnels 

 which increase in size as the larvae grow. When fully grown the larvae change to pupae 

 at the end of the burrows they have formed and when the beetles emerge they eat through 

 the bark and make their escape. In the specimen from which the figure was drawn is 

 evidence that when the female encountered a knot, she backed up and started a tunnel at 

 an angle which caused her to avoid the obstacle. Natural size. 



trees. When hatched the nymphs drop to the ground, burrow into it, 

 and live in chambers on the roots, feeding upon the sap. 



The order Coleoptera (kol e op' ter a; G., koleopteros, sheath- winged), 

 which includes the beetles, contains many destructive forms. Among 

 these are borers in the trunks and hmbs of trees (Fig. 194) and stems of 

 other plants; and the leaf beetles, which destroy fohage. The potato 

 beetle is a leaf beetle. Weevils attack seeds and fruits, carpet beetles 

 injure rugs and carpets, and wire worms damage the roots of plants. 

 Both the larvae and imagos of beetles cause damage. 



The order Lepidoptera (lep i dop' ter a; G., lepidos, scale, and pteron, 

 wing) includes butterflies and moths, which are destructive only in the 

 larval stage. The larvae of some are borers in the stems of plants and 

 those of others eat the foliage. Among those affecting trees are the larvae 

 of the tussock and gypsy moths, the web worm, and the cankerworm. 

 The army worm, the cotton worm, and the corn bollworm injure field 

 crops. The codling moth attacks the fruit of the apple (Fig. 195). The 

 clothes moth is injurious to clothing and other articles made of wool, to 

 furs, and to feathers, and the grain moth destroys stored grain. Most 



