38 



PRINCIPAL CACTUS INSECTS OF UNITED STATES. 



In the same category as the preceding species are four species of the 

 closely allied genus Volueella, namely, esuriens, avida, pmilla, and 

 faseiata. They have been found numerously in practically all locali- 

 ties where cactus insects have been collected, occurring frequently 

 with Gopestylum marginatum Say and other species. 



Hermetia spp. 1 



Almost equally important are two species of Hermetia, namely, 

 chrysopila (fig. 7) and hunteri. The former is much more abundant 

 and occurs from Dallas, Tex., southward to San Antonio and west- 

 ward as far as Los Angeles, Cal. 



The larva? of Heimietia chrysopila Loew measure 35 mm. by 10 mm., 

 the tail 2 mm. The integument is very tough and leathery, dark 

 brown, its surface densely and evenly punctured, with indistinct 



transverse rows of callosi- 

 ties near the posterior 

 third. The head is deeply, 

 longitudinally impressed 

 below, with two longitudi- 

 nal ridges above. 



This species has been 

 collected from April until 

 September and has been 

 observed depositing eggs 

 in the empty cells of Ger- 

 sta>ckeria as well as in the 

 openings made by Melitara 

 and other species. It is 

 not at all restricted to 

 cactus, but undoubtedly 

 breeds in decaying vegetable matter of any description. The adults 

 are found in flowers of many species as well as in those of Opuntia. 

 The most remarkable observation made on this species relates to 

 the longevity of the larva. In May, 1909, a number of specimens 

 which appeared to be nearly full grown were taken at Hondo, Tex., 

 by Mr. J. D. Mitchell. They were placed in breeding cages, from 

 which adults appeared irregularly between July 17 and August 19. 

 Some of the larvae, however, did not yield adults. They remained 

 motionless in the bottom of the cages. Whenever a new supply of 

 food in the form of decaying cactus was introduced they began feed- 

 ing, but as soon as the food dried they became quiescent. After it 

 was observed that they were of rather remarkable longevity no food 

 was introduced for over a year. The larvae lived for more than 15 

 months without food and developed readily later when food was sup- 



PlG. 



-A cactus insect, Hermetia chrysopila: Adult. 

 Enlarged. (Original.) 



'Order I)ipti'ra. family Stratiomyiidffi. 



