Repository: UIHistories Project: Board of Trustees Minutes - 1886 [PAGE 306]

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300 "taken in connection with the culture and infection experiments, to be presently described, we must a least allow them weight as cumulative evidence. Artificial cultures of the cabbage worm bacteria were made by us duing the three seasons of 1883, 1885 and 1886, those of the first two years being exclusively in fluid media—either in beef broth or infusion of cabbage leaves—and those of the present year in both fluids and solids. The details of the methods used can not be given here, but may be found fully described in the technical papers on this class of subjects, published in the bulletins of the Illinois State Laboratory of Natural History. Here I need only say that every precaution known to the practical bacteriologist was used to secure pure cultures and to guard against unwarranted conclusions. As a result of our culture experiments I now consider it thoroughly established that the characteristic micrococcus of the white plague of the cabbage worm is readily cultivable in animal infusions and in solid gelatine media, and that with due care pure fluid cultures may be obtained in condition for successful use in conveying the infection to other insects. The general prevalence of this disease in the regions under my observation has deterred me from experiments intended to test the practicability of conveying it to healthy cabbage worms by means of artificial cultures, as I could have no security that seemingly healthy insects collected for experiment had not already been freely' exposed .to it in the field. I have consequently been reduced to the less promising experiment of infecting the food of other species of larvae with material obtained by cultures from diseased cabbage worms. I say less promising, because my previous experiments for the transfer of other insect diseases from one species to another, have repeatedly proven failures, either partial or complete. In the case of the cabbage worm plague, however, (the most virulent and rapid in its action of any insect disease which I have seen,) the result has been much more encouraging. For example, I fed thirty thistle caterpillars (Pyrameis cardui) August 11 with thistle leaves dipped in a fluid culture of the cabbage worm Micrococcus, and within forty-eight hours twelve of these were dead, their blood and alimentary fluids swarming with the form of Micrococcus ingested. At the end of four days sixteen larvae had died under experiment, two had been killed accidentally, eight had,pupated, and five were yet alive,—a mortality, due to the affection, of fifty-five per' cent, in four days. Solid cultures from these dead larvae gave again the original Micrococcus of the cabbage worm plague. The economic value of our bacterial cultures of the white plague of the cabbage worm is very evident. They might be used to introduce the cabbage worm disease in regions where it had not penetrated. They might be kept over winter, cultivated in spring, and applied to the food of the earliest brood of cabbage worms, with a view to set the disease on foot sooner and with greater energy than if left to itself, and they might be used at any time to intensify the disease already existing, so as to accelerate the destruction of the larvae treated.