NATURAL ENEMIES. 



103 



The development of the embryo can be observed in a general way, 

 with a hand lens, up to and including the sixth stage. This stage is 

 reached, under favorable weather conditions (50° 

 to 75° F.), in about three days. 



A large number of embryos are nearly or quite 

 half grown by the time freezing weather begins, 

 growth starting again with the first warm days 

 of February. We have noted a revolution of the 

 embryo within the egg, and this revolution takes 

 place between figures 1 and 2 of Plate VII. Eggs 

 begin to hatch by the last week in March, the 

 typical appearance of the abandoned eggshell being shown in text 

 figure 18. The number of stem mothers to appear in spring depends 

 to a large extent upon the temperature of the preceding fall. 



Fig. 18.— The spring 

 grain-aphis: Shell of 

 egg after young stem- 

 mother has emerged. 

 Greatly enlarged. 

 (Original.) 



Abbreviations 



A., anterior pole. 



ab 1 , ab 2 , etc., abdominal segments. 



ab. r. abdominal region. 



am., amnion. 



app., appendage. 



at., antenna. 



6. c, blastpderm cell. 



b., blastoderm. 



c. I., cephalic lobes. 



d. o., dorsal organ. 

 ec, ectoderm. 

 en., entoderm. 



g. b., germ band. 

 I., labrum. 

 lab., labium. 

 md., mandible. 



Used in Plates III-VII. 



ms., mesoderm. 



mx., maxilla. 



o., fundament of ovary. 



o. y., ovarian yolk, 



p., posterior pole. 



p. o., "polar organ." 



p. p., peripheral protoplasm. 



p. y., primary yolk. 



pcd., proctodeum. 



s., serosa. 



s. g., salivary gland. 



st., stomodaeum. 



th. app 1 , 2 , etc., thoracic appendages. 



th. r., thoracic region. 



y. c, yolk cells. 



NATURAL ENEMIES. 



Toxoptera graminum is beset by a host of foes, without which we 

 would be powerless to combat it. These enemies naturally group 

 themselves into two classes: First, insects that develop within the 

 body of the " green bug" and are termed true parasites; secondly, 

 those foes that feed upon them externally or that take them directly 

 into their bodies. These latter are termed predatory enemies. Under 

 the true parasites we have Apliidius testaceipes Cress., Apliidius ave- 

 napMs Fitch, ApJiidius confusus Ashm., ApJielinus mail Heild.,ApJie- 

 linus nigritus How., and ApJielinus semiflavus How., all of which are 

 minute four- winged flies ; under predatory enemies there are lady- 

 beetles, syrphids, and cecidomyiids (two-winged flies), lacewing flies, 

 and birds. Besides these, there are secondary parasites, or those that 

 prey upon the true parasites of Toxoptera. These latter are as truly 

 our enemies as are Toxoptera. 



