. Elementary entomology . FIG. 401. Pteromalns pKparntii, a chalcis-fly which parasitizes the cabbage-worm and many other injurious insects. (Greatly enlarged, hair line shows natural size) a, male ; £, female. (After Chittenden, United States Department of Agriculture) cabbage-butterfly caterpillars, from one of whose chrysalids several hundred of the parasitic flies may often be reared, and in some sec- tions entirely prevents the increase of this troublesome garden pest. Many of the species are parasitic in the eggs of insects, while others are the most effective parasites of scale insects.

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. Elementary entomology . FIG. 401. Pteromalns pKparntii, a chalcis-fly which parasitizes the cabbage-worm and many other injurious insects. (Greatly enlarged, hair line shows natural size) a, male ; £, female. (After Chittenden, United States Department of Agriculture) cabbage-butterfly caterpillars, from one of whose chrysalids several hundred of the parasitic flies may often be reared, and in some sec- tions entirely prevents the increase of this troublesome garden pest. Many of the species are parasitic in the eggs of insects, while others are the most effective parasites of scale insects. Unfortunately one or two species are injurious to crops, the best-known example being the joint-worm of wheat (Isosoma tritici], whose larva wrorks in the lower stems, causing gall-like swellings of the joints and weakening them so that the grain is blown over, much the same as when affected by the Hes- sian fly. Smallest of all the par- asites are the little proc- tOtrypids (PrOCtotrypidae), FlG> 402< A chalcis parasite (Chiropachys colon}

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