ELM LEA'F-CURI.. 29I 



ELM • LEAF-CURL. 



A common and widespread enemy to the elm is the plant 

 louse, Schisoneura americana, that causes the leaves to curl and 

 present an unsightly appearance. Fig. 31. 



The deformed leaf serves as a protection to large colonies 

 of the plant Hce, small insects covered with white powder; and 

 contains, besides, the molted skins of the insects and a consid- 

 erable amount of liquid. The liquid, which is excreted by the 

 plant lice, is called honey dew because it is sweet, and is much 

 sought after by ants who prize it highly as food. 



The eggs of this insect live over winter in the crevices of 

 the bark. As soon as the young plant louse hatches in the 

 spring, it crawls out to a tender leaf and settles upon the under 

 side. Here it inserts its beak and sucks the sap for food and 

 the punctured and irritated leaf swells and curls. The indi- 

 viduals of this first generation or stem-mothers are compara- 

 tively large and plump plant lice that never acquire wings. 

 They give rise to innumerable progeny that drain the leaf 

 of sap. 



The leaves become in consquence badly curled and often 

 those near the tip of the twigs are abnormally clustered into 

 a sickly looking mass or rosette. About the time the leaves 

 become yellowish and unsightly enough to attract attention, 

 a generation of the plant lice is developed which acquire wings 

 and fly from the curled leaves for fresh quarters. 



Natural Enemies. Lady beetles, both in the larval and 

 adult stage, feed greedily upon plant lice and often clear a 

 whole tree of these pests. Striped black and yellowish syrphus 

 flies are commonly seen hovering near to deposit eggs and the 

 maggots which hatch from these are exceedingly rapacious, 

 devouring plant louse after plant louse in quick succession. 

 Predaceous bugs, {Camptohrochis grandis and others) are also 

 frequently found feeding upon this species of plant louse. 



Besides these predaceous insects, minute internal parasites 

 develop in the bodies of the plant lice, thus destroying great 

 numbers of them. 



