Heter: 1 



HETERODERA 

 F. W. G. Jones 



LIFE HISTORY 



First, a little about life history. Let us begin consideration 

 of the life cycle with the egg enclosed within the cyst lying in the 

 soil. The nematode is usually induced to hatch, although not always, 

 by means of a root diffusate. The second stage larva, there having 

 already been one molt within the egg, emerges from the cyst and migrates 

 through the soil. Finding a suitable host, the larva invades a root 

 leaving a trail of damaged root cells which may be very easily seen by 

 special preparation. Eventually within the plant the larva begins to 

 swell and goes throurrh another molt which brings it to the third larval 

 stage. It is not easy to distinguish at this third stage between the 

 larvae which are to be males and those to become females. (I am using 

 in reference to this the admirable work on Hete roder a by Dr, Raski*.) 

 It is possible to see the rudiments of what is to become the testes 

 and in the female the bi-lobed ovary. There is more evident differen- 

 tiation of the sexes in the next molt. In the male a certain amount 

 of elongation occurs and you can then see by the time of the molting 

 the fourth stage larva coiled within the cuticle of the previous stage. 

 Before the fourth molt, the ovaries have elongated but have not yet 

 been connected to the exterior of the nematode. The fourth molt occurs 

 and we now have the fully mature stages. The male's stylet has devel- 

 oped and the copulatory spicules are visible and the male breaks out 

 of the "cyst", if I may call it a cyst. This "cyst" is usually slightly 

 different from the female "cyst"; it is more flask-shaped. And, I 

 believe I am correct in saying that, in the earlier stages it lacks 

 the little blip at the end of the larval forms such as occurs in the 

 Meloidogyne , In the female, taking as an example one of the lemon- 

 shaped types, the ovaries make contact to the exterior through the 

 vulva and then a small amount of jelly-like material is extruded. At 

 this time the female is ready for copulation. The male goes into this 

 jelly. One can find, if one examines many specimens, the male tightly 

 coiled about the vulva, I think tliis is, in fact, the act of copulation, 



There are species in the H eterodera in which males are not known 



'/<r Raski, D. J, 19U9. The life history and moroholo>?y of the sugar- 

 beet nematode, Heteroder a schachtii, Schmidt, 

 Phytopathology lO(2)T 13^-iT2.'" 



