20 



BULLETIN" 689, U. S. DEPARTMENT OF AGRICULTURE. 



When handled the nymphs give off a disagreeable odor. This 

 odor is scarcely perceptible in the case of nymphs in the first instar 

 but increases in strength in the succeeding stages. 



PERIODS OF NYMPHAL STAGES. 



Tables IV and V are introduced to show the minimum number of 

 days spent by nymphs from different egg clusters in the five instars. 

 Table IV refers to nymphs kept in the office and Table V to nymphs 

 kept in the insectary. The nymphs issuing from a single egg cluster 

 were kept together in a cloth-covered jar containing moist sand. 

 Green tomatoes were used as food and proved very satisfactory. 

 Fresh ones were placed in the jars at frequent intervals in order that 

 the food supply might approximate that in the field. 



The jars were examined daily, and the dates given for the different 

 lots are those on which the first individual from a certain egg cluster 

 issued from the egg or from a subsequent nymphal instar. It is 

 assumed, therefore, that the first individual to issue from an egg 

 cluster was the first to become adult. 



Individuals from any one egg cluster spent about the same amount 

 of time in either of the first two nymphal instars, but during the 

 later instars the periods became less constant. Temperature condi- 

 tions apparently had an important bearing over this. For instance, 

 during a period of warm weather in the fall a few nymphs in a certain 

 instar would molt; then the temperature would suddenly fall and 

 several days of cool weather follow, no other nymphs molting until 

 this period had elapsed. Periods of several days, therefore, sometimes 

 occurred between the time when the first and last adults appeared. 

 In the fall these periods were sometimes prolonged to 30 days. 



The periods spent by the nymphs of different egg clusters in the 

 succeeding instars were apparently influenced by the prevailing 

 temperatures; low temperatures lengthening the periods. This can 

 be seen by comparing the dates given in Table V with the insectary 

 temperatures shown in figure 13. 



Table IV. — Minimum length of instars of Nezara viridula based on records of first 



individuals. 1 



Lot. 



Hatched. 



Second 

 instar. 



Third 

 instar. 



Fourth 

 instar. 



Fifth 



instar. 



Adult. 



A 



July 2 

 July 4 



July 5 

 July 7 



July 10 

 July 13 



July 20 

 July 19 



July 26 

 July 29 



Aug. 2 



B 



Aug. 8 









Number of days to complete instar. 



A 





3 

 3 



5 10 



6 6 



6 

 10 





B 



10 



I 









1 Average of maximum temperatures to which nymphs were exposed, 89° F.; average cf minimum tem- 

 peratures, 80° F. 



