THE GRAIlSr BUG. 



11 



EELATION OF TEJIPEEATrrKE TO INCUBATION. 



In laboratory experiments and in the field it was observed that 

 variations in temperature had a pronounced influence in determin- 

 ing the length of the egg period. In one experiment half of a newly 

 deposited egg cluster hatched in 4 days when exposed to a maxi- 

 mum daily temperature of 90° F. while the remaining half of the 

 same egg cluster which was exposed to a maximum daily tempera- 

 ture of 70° F. required T daj^s to complete its period of incubation. 

 (See Table I.) 



Table I.- 



-Relatlon of temperature to incubation and nymphal development in 

 Chlorochroa sayi. 



Incuba- 

 tion 

 period. 



First 

 instar. 



Second 

 instar. 



Maximum daily temperature of 70° F 



Maximum daily temperature of 90° F 



Difference for 20° F. of temperature 



Days. 



Days. 



Days. 



DETAILS OF HATCHING. 



^A-lien nearly ready to hatch, the eggs assume a darker color than 

 during the earlier stages of their development. Upon dissecting one 

 of these eggs it is found that the fully developed nymph is inclosed 

 within a delicate transparent membrane. On the outside of this 

 membrane just under the lid of the egg, and at a point opposite the 

 vertex of the head of the inclosed nymph, is a black, chitinized 

 T-shaped structure which functions as a shell burster. The curved 

 top of the T, or shell burster, follows a curved line running from eye 

 to eye of the nymph over the vertex of the head. The shank of the 

 T follows the median dorsal line of the nymph posteriorly. A short, 

 stout spine occupies about one-third of the median portion of the T 

 at the point where the lines intersect. This spine is directed at the 

 suture between the lid and the neck of the egg at a point opposite 

 its hinge. During the process of hatching the struggles of the 

 nymph against the shell burster exert a strong lifting pressure on 

 this spine and the lid of the egg is partially raised. At the same 

 time the inclosing membrane splits just back of the shell burster 

 and slips forward over the head of the nymph. As the integument 

 of the nymph is very soft, the emergence is by slow periodic move- 

 ments apparently exerted from within the body of the nymph. The 

 first portion of the nymph to be free is the first pair of legs, followed 

 by the antennae, rostrum, second pair of legs, third pair of legs, head, 

 thorax, and abdomen in the order named. 



