No. 4.] THE ARMY WORM. 273 



Agawam, to whom I am indebted for much valuable informa- 

 tion concerning the habits of the army worm, writes me that 

 the greater part of the pupte of tlii.s insect found while plough- 

 ing the infested fields were parasitized, thus showing that in 

 some parts of the State the parasitic flies have been of mate- 

 rial assistance in destroying this pest. 



Causes Governing Outbreaks of the Army Worm. 



In view of the abundance of the army worm during the 

 present summer it may l)e profital)le to briefly review the 

 causes leading to sucli outbreaks and the influences which 

 control tlie same. The army worm is an insect which ap- 

 pears as a pest only at extended intervals or times. This 

 seems chiefly due to the warfare waged upon it by its natural 

 enemies, mainly parasites, predaceous insects and birds, and 

 also to some extent to climatic conditions. 



Parasites often confine themselves to one host and their 

 abundance is regulated by the numbers of the host, while 

 l)irds as a rule seem to prefer the most abundant form of 

 acceptable insect food. The climate aftects insect increase 

 either through the abundance or scarcity of the food supply 

 or through conditions favorable or unfavorable to the mul- 

 tiplication of natural enemies. 



The relationship between an insect and its natural enemies 

 is seldom equally balanced ; that is to say, the one form or 

 the other is the more aljundant in the point of uuml^ers or 

 more efiective by reason of peculiarities favorable to its in- 

 crease. Hence, in years when the army worm is not present 

 in any considerable number its parasites are limited in their 

 multiplication by the scarcity of the host, while the birds 

 give their chief attention to other insects more abundant. 

 Thus the army worm increases slowly in numbers from year 

 to year. Finally there comes a season especially favorable 

 for its development and the worms appear in numbers suf- 

 ficient to attract some degree of attention. They are fol- 

 lowed the next year by a more or less wide-spread outbreak.* 



* I am informed by Secretary Wm. R. Sessions that from careful ol)servations ex- 

 tending over aconsideraI)lc period of years he has reached the conclusion that army 

 worm outbreaks usually follow a warm, dry sprinji. It seems quite prol)able that, 

 as pointed out by Mr. Sessions, such conditions of warmth and dryness are favorable 

 to the emerging of the moths and the hatching of the eggs. 



