THE CONCHUELA. 



39 



head and along the venter as the emergence progresses. The position 

 of the nymph in the egg is with the dorsum toward the hinge of the 

 Ud. The antennae and legs are closely appressed to the body and 

 extended directly backward. Movement of the antennse and legs 

 begins as soon as they are free from the egg and emergence is not 

 completed until the legs are sufficiently strong to enable the insect to 

 cling to the egg-batch. Individual nymphs have been observed to 

 emerge in from 12 to 15 minutes after the hd is first raised. Emer- 

 gence of nymphs from a batch of eggs usually extends over a period 

 of less than 1^ hours, but activities in this line as in others are largely 

 under the influence of temperature. A record on October 10 shows a 

 difference of 2 hours and 15 minutes between the appearance of the 

 first nymphs and last nymphs to emerge from a batch of 13 eggs. 



Nymphs. 



DURATION OF NYMPHAL STAGES, 



Under normal summer temperatures. — In spite of the most careful 

 attention one can reasonably give, the death rate of Pentatomid 

 nymphs under observation in the laboratory is very high. In no 

 case were nymphs of the conchuela reared to maturity in the labora- 

 tory, but the duration of the various stages was determined by more 

 than 35 individual records. The prevailing temperature conditions 

 seem to control the duration of the nymphal stages of these and other 

 Pentatomids, while a lack of food supply seems to result only in either 

 a stunted growth or death from starvation. During the months of 

 July and August, 1905, at Tlahualilo, Durango, Mexico, and Dallas, 

 Tex., respectively, the data summarized in the following table were 

 obtained, being based on from 5 to 35 specimens in each instar. 



Table XVI. — Observations on duration of nymphal stages of the conchuela. 



stage. 



Average 

 duration. 



Minimum 

 duration. 



Maximum 

 duration. 



First instar 



Days. 



4.5 

 6 

 8 

 8 

 12 



Days. 



4 

 5 

 6 

 5 



Days. 



5 



Second instar 



7 



Third instar . 



10 



Fourth instar 



12 



Fifth instar 



17 







All nymphal instars . . 



38.5 



27 



51 







It is very unlikely that the maximum duration of each stage given 

 above would ever be equaled by a single specimen passing through the 

 successive stages, even in the laboratory during the summer months. 

 It is, moreover, probable that under out-of-door temperature condi- 

 tions the average duration of all nymphal instars taken together is a 

 few days less than the average obtained by the laboratory observations. 



