. Elementary principles of agriculture; a text book for the common schools. us Insects 175 grain, and, after feeding on the starchy matter for aboutthree weeks, form a thin silken cocoon, from which theadult moth emerges in a few days. About thirty-fiv^days are used in passing from egg to adult. Four to,possibly, eight broods mature during the year. Whengrain is stored in bulk, only the surface layers are in-fested. Both the weevils and moths are subject to attacksby parasites. 242. Preventing Injury to Stored Grain. To reducethe injury to stored grain, use is made of repellants likenapthalene
. Elementary principles of agriculture; a text book for the common schools. us Insects 175 grain, and, after feeding on the starchy matter for aboutthree weeks, form a thin silken cocoon, from which theadult moth emerges in a few days. About thirty-fiv^days are used in passing from egg to adult. Four to,possibly, eight broods mature during the year. Whengrain is stored in bulk, only the surface layers are in-fested. Both the weevils and moths are subject to attacksby parasites. 242. Preventing Injury to Stored Grain. To reducethe injury to stored grain, use is made of repellants likenapthalene (so-called moth balls), salt, air-slakedlime, and other substances which, while not poisonous,drive the insect out. A temperature of 125° Fahr. issufficient to kill weevils, though more than 150° be endured by dry grain without loss of ger-minatmg power. Treating the grains to the vapors ofbisulfide of carbon in tight bins is by far the most satis-factory means of protecting stored grain. In destroyingthe insects, use one pound to one hundred bushels Fig. 112. Angoumois grain moth. CHAPTER XXIVUSEFUL INSECTS 243. Useful Insects. Some insects are useful becausethey supply food, as the honey-bee. Others supplymaterials for clothing, as the silkworm. Still others, aswe have seen, cause flowers to set fruit by carryingpollen from flower to flower. (See H 167.) There aremany species which are especially useful in mans battlewith the forces of nature, because they prey upon theinjurious insects. 244. Wasps. There are many kinds of wasps. Thecommon red wasps and yellow jackets, with theirpaper nests made out of the fragments of plants, arewell known. The mud-dauber is another common are many species of wasps that do not live incolonies hke the ones just mentioned, but live singly,and are, hence, called solitary wasps. The wasps aresomewhat related to the domestic bees, and bumble-bees. But instead of storing nectar and pollen for food,as the bees do, t
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