. Agricultural zoology. Zoology. INSECTS. 133 host by bringing the tip of its abdomen (where the main stem of the air-tube system opens) into con- nection with one of the host's spiracles. Since the larva feeds altogether upon perfectly digestible sub- stances an anus is superfluous and is absent. Many ichneumon larvse are ready to become pupse when the host is about to pass into the same condition; the larva then bores through the skin of the latter, which quickly dies. Other species do not attack the organs of the host so soon, but allow it to become a. Fig. 90.—The Yellow-legged Ichneumon '
. Agricultural zoology. Zoology. INSECTS. 133 host by bringing the tip of its abdomen (where the main stem of the air-tube system opens) into con- nection with one of the host's spiracles. Since the larva feeds altogether upon perfectly digestible sub- stances an anus is superfluous and is absent. Many ichneumon larvse are ready to become pupse when the host is about to pass into the same condition; the larva then bores through the skin of the latter, which quickly dies. Other species do not attack the organs of the host so soon, but allow it to become a. Fig. 90.—The Yellow-legged Ichneumon 'Fly (^Afic^'ogaster glomeratus) of the Cabbage Caterpillar. Left, the adult insect; right, the larva (both enlarged). In the middk, Cabbage Caterpillar and a heap of Microgaster pup^e. pupa in peace, and then themselves become pupge inside it; later on, one or several ichneumon flies come out of this pupa instead of a moth or butterfly. It is obvious that ichneumon flies are very serviceable by destroying a large number of harmful insects. They cannot, indeed, prevent the increase of any particular noxious insect, but, when this takes place, they themselves increase to a greater extent, and finally appear in such numbers as to make an end of the pest. I shall not enumerate here all the various ichneumon flies which benefit agriculture, but simply mention the Small Cabbage Caterpillar Ichneumon Fly (Micro- gaster glomeratus), depicted in Fig. 90, which, like its host (the large cabbage white), appears in two generations. The larvae of the ichneumon fly live in large numbers in the large cabbage caterpillar, and at their last moult acquire minute teeth, with which they bite through the skin of their host; they then. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bos, Jan Ritzema, 1850-1928; Ainsworth Davis,
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1894
