298 RErORT OF THE COMMISSIONER OF AGRICULTURE. 



PARASITES. 



The abundance of the true parasites of the eottou-worm, and the num- 

 ber iu which they occur, render their consideration of the highest i>rac- 

 tical importance. 



Taking into consideration the number and variety of these friends of 

 the planter, and the way in which they make themselves obvious to 

 every one who tries to work out the life history of tlie cotton-worm, it 

 seems very strange that several recent writers should have entirely 

 overlooked their presence. Mr. Grote, in his paper before the Ameri- 

 can Association for the Advancement of Science, stated that he had 

 never been able to observe any parasites, although he admitted that 

 such might exist; and Professor Riley, iu the 1878 circular of this 

 department, states that no enemies of the cotton-worm have hitherto 

 been reported. We mention these two instances in particular, because 

 the undoubted ability of these naturalists renders their statements all 

 the more singular. The fact is that not only were parasites well known to 

 many observers throughout the South, but no less than six accounts 

 had been published with tolerable popular descriptions of Pimpla con- 

 quisitor (a large ichneumon which extensively infests the last brood of 

 the worms, issuing from the chrysalis in midwinter or early spring), and 

 two very fair figures had also been published. 



Let us now enter into a detailed account of these parasites. Up to 

 the time of the present writing thirteen distinct species parasitic ui)on 

 the cotton- worm, iu one or another of its stages, have been bred in the 

 department. Of these, eight species are hymenopterous and five dipte- 

 rous. 



The COTTON-TVORM-EGa parasite {Trichogramma pretiosa, Eiley). — 

 In the latter part of the summer of 1878 a small lot of cotton- worm eggs 

 were received at the department. The eggs were placed in a glass 

 breeding-jar, but much more than the usual time seemed to elapse be- 

 fore the hatching. One morning, however, a number of very minute 

 flies, so small as scarcely to be seen with the naked eye, were found fly- 

 ing around the jar, and the eggs were empty. Here, then, was a true 

 egg-parasite, the mother fly having laid her egg within the egg of the 

 cotton-moth, and her progeny having lived and undergone its transfor- 

 mations within that limited space. Whether more than one parasite 

 issued from a single egg was not determined. These parasites belonged 

 to the great hymenopterous family Ghalcididae. 



The species under consideration is one of remarkable beauty. The 

 general color is yellow, with brilliant red eyes. The wings are very del- 

 icate and transparent and present prismatic colors when viewed in dif- 

 ferent lights. The wings 'are fringed with excessively fine hairs; their 

 surface is also covered with still finer hairs. In length they are only a 

 trifle more than one-hundi-edth of an inch (.3'"™), but, like all of the 

 subfamily to which they belong, are very active and are great leapers, 

 springing sometimes to a distance of two or three inches. 



An allied species {THcliorjramma minuia) has been reared from the 

 eggs of the dissippus butterfly (Xiwjenitis dissippus, Godt.). In this case 

 from four to six individuals have been reared from a single egg of the 

 butterfly, and this seems to be about the normal number. It is prob- 

 able, then, that more than one parasitic egg is laid within the egg of the 

 cotton-moth. Plate XII, Fig. 14 (T. minuta, Eiley) wiU give a very 

 good idea of the general ajipearance of the magnified insect.* 



*The technical description of T. pretiosa, Riley, was pulblislied in the Canadian En- 

 tomologist for Septemljer, 1879, and in onr special report, p. 194. 



