58 



SEASONS MOST FAVOKABLE TO ITS RAPID INCREASE. 



It has been frequently observed that the Army Worms are most 

 abundant during a wet season, and this fact has given rise in many 

 minds to the belief that such seasons are most favorable to their 

 rapid development ; but T am strongly of the opinion that this belief 

 is erroneous. 



It is well known that insects develop most rapidly in warm, dry 

 weather; in fact, moisture is known to be very injurious to the 

 health of many kinds. This is known to be the case with the com- 

 mon Silk Worm {Sericaria mori, Linn.), and I have proved it to be 

 so with the Celery Worm (Plusia simplex, Guenee), an insect that 

 has been quite destructive to lettuce in a few gardens in this local- 

 ity the past season. A brood of these worms which I reared from 

 the eggs, on perfectly dry leaves — that is, leaves that were free from 

 moisture — until they were nearly full grown, appeared to be very 

 costive ; supposing this to be due to a lack of moisture, I dipped 

 some leaves into water and fed them to the worms. Shortly after 

 this the worms were taken with a kind of dysentery, which so reduced 

 them that in a short time all but one died. This one in a few 

 days assumed the chrysalis form, but died before producing the 

 moth. 



I have but little doubt that wet food has the same effect on the 

 Army Worms that it has on those mentioned above. Of the twenty- 

 eight Army Worms which I collected in the Hungarian field, and 

 which had no Tachina eggs attached to their bodies, only three — or 

 about one-ninth of their entire number — died from some unknown 

 cause ; while in confinement they were fed on perfectly dry, but 

 green, leaves. The weather for over a month previous to the date 

 of collecting them (July 18) had been very dry; a week or so after 

 this there came a heavy rain-storm, and from this date up to the 

 month of November a greater amount of rain fell than was ever 

 known to have fallen in this period for many years past. Out of 

 the five Army Worms which I took in September, two — or nearly 

 one-half of the whole number — died from some unknown cause ; they 

 were reared in the same manner and in the same place as the 

 others. They died soon after being captured, and shortly after death 

 their bodies turned black precisely as the bodies of the Celery Worms 

 had done. I can assign no reason for this except it be that they 

 died of the same disease, which was produced by devouring wet 

 food. 



Not only is rain injurious to the health of these insects by force- 

 ing them to eat wet food or starve to death, but it also tends to 

 prevent them from developing rapidly by reducing the temperature, 

 as it is a well established fact, and perfectly consistent with reason, 

 that insects develop more rapidly under a moderately high, than 

 under a low temperature. 



In their various functions insects approach much nearer to plants 

 than the higher animals do ; in fact, the mode of living and repro- 

 duction of some insects — such as the Plant-lice and kindred insects 

 —and plants, is very striking. In view of this fact we naturally 

 infer that any change in the temperature which produces a given 

 effect in plants, will produce a like effect in insects. 



