40 BULLETIN 191, U. S. DEPARTMENT OF AGRICULTURE. 



stantly in any given direction, hence they seldom get far from the 

 point of emergence. Larvae have been observed to travel 15 feet on 

 concrete Boors, but in the field, under usual conditions, they enter 

 the soil to pupate directly beneath the host fruit and do not exercise 

 to any extent this power of locomotion. When the sell is very hard 

 the larvae pupate beneath an} 7 object, or even upon a bare surface, as 

 the floor of a room. On hard moist soils larvae usually pupate upon 

 or just beneath the surface. In the more porous soils pupation oc- 

 curs at various depths, but rarely deeper than from 1 to 1^ inches. 

 It is seldom that larvae are unable to find their way out of their 

 host, but when they can not the} 7 sometimes pupate within the host. 

 Larvae have been known to pupate in bean pods where the} T are 

 imprisoned by the drying out of the pod. Pupation is apt to occur 

 in any of the more firmly textured host fruits. 



PREPUPAL PERIOD. 



The writers have chosen to look upon the pupal stage as beginning 

 with the formation of the puparium and to refer to the duration of 

 the pupal stage as that period between the formation of the 

 puparium and the emergence of the adult. During the warmer sea- 

 sons the contraction of the larvae to form the puparium begins very 

 soon after the larva emerges from the host fruit, and is completed 

 within an hour. Larvae forced to leave fruit prematurely may 

 remain active for as long as two days under certain conditions, but 

 invariably die without forming a puparium if the puparium is not 

 formed for so long a time after emergence. Fifteen puparia formed 

 between 11 a. m. and 1 p. m.. February 3. were dissected one day 

 later, but there was no indication of a true pupa within; no organi- 

 zation of internal structures could be seen except a pulsating heart. 

 On February 5, however, or two days after the formation of the 

 puparium, the examination of 15 puparia showed the true pupa, 

 which was well formed and free within the puparium case. The 

 average mean temperature during this 2-day period was 72° F., 

 with a daily average of from 66° to 78° F. The relative mean 

 humidity ranged between 7~> and 78 per cent. 



THE PUPA. 



DESCRIPTION. 



Puparium (fig. 10). — Length about 5 to mm. Elliptical, varying in color 

 from dark testaceous to dull white, according to host. Being composed of 

 the larval skin, it is natural that the markings of the larva should be found 

 on the puparium. The puparium appears to consist of 12 segments, although 

 when treated with potash the first is found to be composed of the first and 



