. La Entomología elementales. La Entomología. 250 Entomología elementales y sólo estamos empezando a aprender a utilizarlas en com- bating importados de los insectos. Así, el estado de Massachusetts y de los Estados Unidos Oficina de Entomolog)' ahora están llevando a cabo experimentos tensive ex- en la importación de los parásitos de los gitanos y de color marrón-tail de las polillas, que son muy eficaces en mantener esos insectos en control en Europa. Los diversos parásitos que atacan los huevos y orugas en las diferentes etapas de crecimiento han sido importados; son criados en este país hasta que suf- ficiently numerosas, y

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. Elementary entomology. Entomology. 250 ELEMENTARY ENTOMOLOGY and we are just commencing to learn how to utilize them in com- bating imported insects. Thus the state of Massachusetts and the United States Bureau of Entomolog)' are now carrying on ex- tensive experiments in the importation of the parasites of the gypsy and brown-tail moths, which are very largely effective in holding those insects in control in Europe. The various parasites which attack the eggs and caterpillars at different stages of growth have been imported; they are reared in this country until suf- ficiently numerous, and are then liberated in sections badly affected by the caterpillars, with the hope that they will ultimately become numerous enough to hold their hosts in check. Ichneumon-flies (Ichneumonidae). Any one who has attempted to rear any of our large moths, such as the cecropia or polyphemus moths (see page 215), will have be- come acquainted with the Ophion flies, which commonly parasitize them. They are light brown or golden in color, about three fourths of an inch long, and the abdomen is compressed laterally, so that the back is ridged. A single ^g^ is laid on the caterpillar, which lives to pupate. The Ophion larva spins a tough brown cocoon within the pupal shell and emerges from it the next spring. They belong to the large family of ichneumon-flies, which includes most of the larger par- asites, though some of this family are quite small. The Pinipla flies are nearly the same size, but are black in color and have the abdomen more broadly joined to the thorax. They are effective parasites of many of our most common caterpillars, such as the tent caterpillar, tussock-moth caterpillars, the cotton-worm, and others. Braconid-flies (Braconidae). Wherever plant-lice are abundant there will be found some empty brown skins, globular in form and with a small round hole in each. Other individuals will be brown, swollen, and dying as a result of the parasitism of little braconid, flies w