76 U.S. NATIONAL MUSEUM BULLETIN 25 6 



records of its existence were made in localities other than Florida 

 Canyon. Despite the fact that the insect was not found in the Mexican 

 State of Chihuahua, its range possibly extends northward from Du- 

 rango along the mountains of the main divide in the extreme western 

 section of Chihuahua into southern Arizona. Another theory is that 

 its occurrence in Florida Canyon is fortuitous and may have arisen 

 through the importation of prickly pear from Mexico for garden 

 culture at Tucson. 



The host plants are Platyopuntias. In Mexico tree and semitree 

 pears (much more numerous than shrub pears) are the usual food 

 plants, the records including Opuntia tomentosa, 0. streptacantha, 0. 

 hyptiacantha, 0. lasiacantha, 0. leucotricha, 0. robusta, and 0. fuliginosa; 

 the shrub pear 0. cantabrigiensis, is occasionally attacked. The larvae 

 found at Tampico were inhabiting an undetermined, erect, brittle- 

 jointed prickly pear related to 0. jamaicensis. In Arizona semitree 

 pears are nonexistent, and the host plants in Florida Canyon were 

 the shrubby 0. canada, 0. discata, and 0. chlorotica. Under cage con- 

 ditions at Uvalde, Texas, the larvae developed readily in the shrub 

 pear 0. lindheimeri. 



The moth has a wing expanse of 1]^ to 1% inches; the forewings 

 are dusky yellow with dark transverse markings; the hindwings are 

 whitish with a dark outer line and a fine wav)'- line in the center. 

 The newly hatched larvae are brown with pronounced dark markings, 

 although the color gradually becomes lighter and the markings fainter, 

 and full-grown lar\'ae are creamy-white with a light brown spot on 

 each side of each segment. 



Megastes was studied at Uvalde, Texas, in 1926-28, at San Luis 

 Potosi, Mexico, in 1930-31, and at Cuernavaca, Mexico, in 1933-35, 

 but, owing to the disinclination of the moths to oviposit in captivity 

 and to the susceptibility of caged larvae to disease epidemic, data 

 on various phases of the life history were rather meager. 



Both cage records and field observations indicate that there are two 

 generations annually. The winter is spent in the larval stage. Pupation 

 takes place in May and June, and the adults emerge in June and July. 

 At Uvalde in 1926 larvae from eggs laid in June and July developed 

 rapidly and started to pupate at the end of July; the first adult emerged 

 on August 10, after a life cycle of 52 days. In Mexico very small larvae 

 have been observed rather generally in September and October, in- 

 dicating that a complete generation must have intervened after June- 

 July emergence. 



The moths have not survived for longer than 3 days in confinement. 

 Little is known about the sex proportions; in one batch of 372 moths, 

 166 (about 44.6 percent) were females. Similarly there is not much in- 



