14 DEPARTMEISTT BULI^TIN •779. 



Similar results were obtained as a result of life-history experi- 

 ments during 1915. 



The death rate of nymphs under observation in the laboratory 

 was very high and increased the difficulty in obtaining data on the 

 length of the different stages, but it ^is believed that the durations of 

 the instars given above coincide very closely with the actual periods 

 occupied by the nymphs in the field. 



DETAILS OF MOLTING. 



When the nymph is preparing to molt it generally assumes a posi- 

 tion with the head downward. After a quiescent period varying 

 from 15 to 50 minutes the process of molting begins. - The thorax first 

 splits down the median dorsal line, then the integument connecting 

 the dorsal plates of the head and thorax splits transversely, allowing 

 the head to fall forward. The thoracic region now becomes elevated, 

 as a result of pressure exerted from within, and the split in the molt- 

 ing skin more pronounced. This causes a transverse separation of 

 the integument connecting the dorsal plates of the thorax and abdo- 

 men to a point nearly as far as the lateral edges of the dorsal thoracic 

 sclerites. The molting nymph first extracts the head and its ap- 

 pendages and then the first, second, and third pairs of legs. As soon 

 as the legs are free they are used as a lever in extracting the remainder 

 of the thorax and abdomen from the molted skin. In four instances 

 under observation the process of molting required from 9 to 12 

 minutes. 



The newly molted nymph appears to be prepared to resume its ac- 

 tivities within a few moments after the completion of its molt. 



With the exception of the ruptures noted above, the cast nymphal 

 skin remains intact and greatly resembles a living nymph. 



BELATION OF TEMPEEATUEE TO NYMPHAL DEVELOPMENT. 



In order to deterpiine the relation of temperature to nymphal de- 

 velopment an equal number of nymphs hatching at the same time 

 from the same egg cluster were kept under maximum daily tempera- 

 tures of 70° and 90° F., respectively. The nymphs developing under 

 the lower temperature required an average of 5 days longer for the 

 first instar and 7 days longer for the second instar. (See Table I.) 

 It is evident that cool weather retards nymphal development to a 

 marked degree. 



ADULTS. 



PERIOD BETWEEN MATUEXTY AND BEGINNING OF OVIPOSITION. 



The ovaries of newly matured females do not contain eggs. In a 

 series of laboratory experiments wherein pairs of reared adults were 

 confined in individual cages, the minimum period between maturity 



