352 



PSrCHE. 



[March 1896. 



presence of males. Many of them are 

 provided with wings but the majority 

 are wingless. This method of repro- 

 duction is continued throughout the 

 warm season, but on the approach of 

 cold weather a true sexual generation is 

 produced, tiie males of which may be 

 either winged or wingless while the 

 females are always wingless. Sexual 

 union between these two forms takes 

 place, and the females deposit true eggs. 

 These pass through the winter, and in 

 spring hatch into stem-mothers which 

 renew the cycle of existence. 



The great majority of aphides pass 

 through the winter in the egg state. 

 This is doubtless the safest way, for 

 even supposing the viviparous or sexed 

 forms capable of enduring intense cold, 

 they would be much more liable to be 

 eaten by birds, scattered by winds or 

 washed away by floods, than the eggs. 

 The latter are nearly always at least 

 partially secured against these vicissi- 

 tudes, although doubtless millions of 

 them perish from exposure to the 

 elements, or are gobbled up by the 

 hungry beaks of chickadees and other 

 winter birds. But as a rule the eggs 

 are so small and so carefully stowed 

 away, that a sufHcient number to propa- 

 gate the species survive all perils. 



Perhaps as simple a method of pro- 

 viding for the eggs as any is that 

 adopted by a handsome yellow Callip- 

 terus (C discolor Monell) which I 

 studied in Illinois a few years ago. 

 This species lives on the under side of 

 oak leaves, particularly the Burr Oak 

 {^iterciis wacrocarpa) generally on 



limited colonies. In autumn a sexed 

 generation is produced, the males 

 having wings and the oviparous 

 females being provided with a long, 

 tapering ovipositor by means of which 

 they push the eggs through the dense 

 pubescence on the under side of the 

 leaf, generally fastening it firmly 

 against the mid-rib. Many of these 

 leaves remain on the tree until quite 

 late in spring ; and it is fair to pre- 

 sume that a sufHcient proportion of the 

 aphides hatch before the leaves fall 

 ofl', climb upon the twigs and begin 

 sucking at the buds, although this has 

 not so far as I know been observed. 

 The eggs are certainly safer hidden 

 in the pubescence of the leaves, from 

 observation by birds, than they would 

 be upon the twigs. 



From fastening the egrr to tiie leaf to 

 attaching it to the bark of the twig- 

 is a short step, and one which appears 

 to have been taken by a majority of the 

 aphides affecting trees and shrubs. In 

 many cases it has naturally resulted 

 from tlie insects being compelled to 

 migrate to the twigs by the early falling 

 of the leaves. In many of the states in 

 the valleys of the Mississippi and its 

 tributaries where the Box Elder or Ash- 

 leaved Maple {JVeg'ufido aceroides) is 

 abundant, its foliage is often infested by 

 a small aphid of the genus Chaitophorus 

 (C. negiiudoidcs) . In autumn the 

 sexed forms leave the falling leaves and 

 congregate in great numbers on the 

 twigs. The males are wingless little 

 creatures with slender flattened bodies, 

 barely two millimeters in length, and 



