410 



THE AGRICULTURAL NEWS, 



December 23, 1911. 



INSECT NOTES. 



A DISEASE OF GRASSROPPERS. 



The present interest in the control of insect pests by 

 assisting in their destruction by means of bacteria and fungi 

 renders important a paper which was read recently before 

 the Academie des Sciences, l^aris. This is reproduced in the 

 Journal d' Agriculture Tropicale for August 1911, p. 238, 

 and the matter in the article is utilized in presenting the 

 following which is partly a free translation. 



At the commencement of the year 1910, the author 

 observed an epidemic disease of bacterial origin i aging among 

 grasshoppers in Yucatan (Mexico); the species indigenous to 

 this part of the world is the same as that in the West Indies 

 — Schistocerca pallens. In all dead grasshoppers examined 

 the presence was noticed, in the intestinal tube, of numerous 

 coccus bacilli which were isolated; these were not seen in 

 grasshoppers ca['tured where the disease was not present, and 

 always on the contrary, it was found in insects, dead or dying, 

 whether they had been infected naturally or artificially. In 

 some cases, even, an almost pure culture of the organism was 

 found in the intestine of the dead insects. The following 

 experiments demonstrate sufficiently the pathogenic nature of 

 the bacillus. 



On May 12, twenty-four grasshoppers were inoculated 

 with a drop of a culture in broth, twenty-four hours old, the 

 needle being forced in lietween the second and third anterior 

 rings; all the infects died in one to twenty-three hours after 

 the injection. Twenty-four other, uninoculated, insects, used 

 as a control, were injected in the same way with a drop of 

 tap water; none were dead, after four days. 



On the same day, a drop of the same culture was placed 

 by means of a pipette on the buccal orifice of twenty -four 

 grasshoppers; they all died in ten to thirty-two hours. 

 Twenty-four control insects were still alive, ten days later. 



The digestive" system of all the dead grasshoppers con- 

 tains a blackish liquid in which the .specific microorganism 

 swarms, and this is found in the same way in the tis.sues. 

 The inoculation of broth with the intestinal contents always 

 gave an almost pure culture of the bacillus. 



On May 15, twelve healthy grasshoppers were placed 

 Under a bell-jar, with the corpse of another specimen which 

 had died after ingesting a drop of the culture. Of the 

 twelve living insects, only two devoured the corpse supplied 

 to them ; one of these died nine hours after the infecting 

 meal ; the otlier about twelve hours afterwards. The ten 

 grasshoppers which had not touched the corpse were still 

 living, ten days later. In another experiment, five of the 

 insects out of tweWe ate the corpse, and were dead between 

 .seven and fourteen hours afterwards. These experiments, 

 repeated several limes, show that the cause of the disease is 

 the coccus bacillus that was the subject of the study. This 

 is very mobile and bears cilia all over its surface: in one 

 and the same culture there were observed slightly ovoid 

 forms measuring 05 microns, together with bacillary forms 

 measuring 10 to 0-5 microns. The organism does not stain 

 with Gram, but easily takes up aniline colours. In young 

 cultures and in the intestines of the grasshopper, the bacillus 

 stains most strongly at the extremities. It is a facultative 

 aerobe, that is to say, it can live either with or without air, 

 but preferably with air. It affords cultures between the tem- 

 peratures of 16° 0. and 43° C, and develops very rapidly in 

 ordinary broth at 37° C. In this ca.se, cloiiding appears 

 after the fourth hCur and gradually increases; at the end of 

 thirty-six to forty-eight hours, a thin coat is formed at the 



surface, and at the same time a deposit appears at the bottom 

 of the tube, without any clarification of the medium. 



In gelatine, in eighteen hours, the cultures show a thin 

 white line, granular in appearance, which does not develop 

 to such an extlflprt in the depths of the culture as it does near 

 the surface. This takes the shape of a nail on the surface; 

 at I he end of eight days liquefaction commences there, and 

 proceeds alongj.the track of the needle in the form of the 

 finger of a gloVe. In streak cultures, a thin whitish line is 

 obtained which»sho\vs a bluish tint; the track broadens until 

 the eighth day, to a breadth of 2 ram. when the gelatine liqui- 

 fies. Plate cul^^ures exhibit, in eighteen hours, small colonies 

 having a diameter of 1 mm.: these are transparent, with 

 an irregular outline, and toward the fourth day become 

 opaque and yellow. On gelose, at 37° 0, round colonies develop, 

 which are whitiSb, sticky and translucent and possess a diame- 

 ter of 1 to 2 mm., the surface being wrinkled. In the body of 

 the medium, small, lenticular, opaque colonies arise. In 

 a streak culture in an inclined tube, the surface is rapidly 

 overrun, and eventually a thin whitish layer is formed. 

 The odour of the cultures recalls that of broth from Liebig's 

 extract. 



In successive cultures, the bacillus rapidly loses its 

 virulence. The first culture, administered by the mouth, 

 kills the insect in 8 to 24 hours; the second in 12 to 36 

 hours, the third in 36 to 96 hours; after this stage of 

 succe.ssive cultVfVes, the grasshoppers recover. The fourth 

 culture permits half of the insects to survive, the tenth 

 does not kill when it is administered by the mouth. Cfltures 

 can be caused to regain their virulence by successive injec- 

 tions of several drops into the abdominal cavity of grass- 

 hoppers; after three repetitions they are sufficiently virulent 

 to kill, when injected, in 5 to 6 hours, and when administered 

 by the mouth, in 8 to 12 hours. 



The author was not able to kill, by causing them to 

 injest cultures which were virulent, grasshoppers that had 

 recovered after taking the attenuated cultures. In view of 

 the fact that, ordinarily, grasshoppers died in all cases where 

 a drop of the virulent culture had been absorbed by them, 

 it is natural to conclude that immunity is acquired after 

 a benign attack of the disease. 



Observations were made of flights of gras.shoppers when 

 the disease was raging. In these, of twenty-five gras.shoppers 

 captured and chosen among the most lively, six died in three 

 days, and the others survived; among the nineteen remaining 

 insects, which were dis.sected after having been under observa- 

 tion for eight days, five gave evidence of the presence of the 

 specific coccus bacillus in the intestinal contents, and at the 

 same time did not appear to be suffering from the disease. 

 It w.is proved that this coccus bacillus was actually the speci- 

 fic organism, and that it was virulent. These observations 

 lead to the conclusion that the proportion of grasshoppers 

 acquiring immunity is 20 to 25 per cent. As it is impossible 

 to keep the in.sects in captivity more than fifteen days, the 

 observer was not able to determine the duration of this 

 accjuired iminun\ty. 



Information supplied by the planters in Yucatan, in 

 March 1911, wag to the effect that the number of gnisshop- 

 pers had diminished to such an extent that the damage from 

 them, this year, was considered to be of little importance; 

 the disease was continuing to rage in the succeeding flights. 



The specific <irganism does not cause sickness in the 

 fowl, the guinea pig, or the rabbit. 



The article concludes with the suggestion that it would 

 be of interest to introduce into other countries the disea.se 

 attacking grasshoppers in Yucatan, with an effort to utilize 

 the bacillus for the control of this pest in those countries. 



