CACTUS-FEEDING INSECTS AND MITES 75 



The sole species of prickly pear native to the Galapagos Islands is 

 the extremely variable Opuntia galapageia which may be a low-growing 

 creeping plant or which may grow erect to a height of 30 feet. The 

 larva, solitary in habit, forms within the Opuntia segments a rather 

 commodious tunnel weakly lined with silk and opening to the exterior 

 by a delicate silken tube. The full-grown larvae are dirty white, pink 

 dorsally, with brown plates. The stout cocoon is attached to the exterior 

 of the plant and is covered with prickly pear spines, lichens, and other 

 available material. The large grey-brown moths with a wing expanse 

 of 2 to 3 inches emerge in September and October. Williams states 

 that Beebea Schaus is evidently widely distributed in the Galapagos 

 group. 



Lepidoptera : Pyraustidae 



MEGASTES Guen^e 



The following pyraustid species was formerly placed in the genus 

 Laniifera Hampson. 



Megastes cyclades (Druce) 



On account of the truly social habit of the larvae, which live in colonies 

 within the segments and stems of prickly pear after the manner of the 

 various species of Melitara and Cactoblastis, this distinctive insect de- 

 serves more than passing notice. 



Megastes is widely distributed in Mexico, from Durango and the 

 mountainous section between Victoria and Tula in the southwest 

 of the State of Tamaulipas in the north as far south as Oaxaca. It 

 appears to be most abundant around Aguascalientes, occurs in scat- 

 tered quantity in the neighbourhood of San Luis Potosi and Mexico 

 City, and has been collected at many other localities such as Guadala- 

 jara and Techuacan. The distribution was thought to be restricted 

 to elevations of between 5,000 and 8,000 feet on the Central Plateau, 

 but in April 1931 one colony of larvae was observed near Tampico 

 on the gulf coast. 



In addition to the Mexican distribution, this insect is known to 

 occur in one small area in the Tucson region of southern Arizona. 

 In May 1924 Dr. Vorbies of the University of Arizona found larvae 

 in the Florida Canyon of the Santa Rita Mountains about 25 miles 

 southeast of Tucson. Officers of the Board had no difficulty in locating 

 material in Florida Canyon in 1925 and 1926, but in June 1928 con- 

 siderable searching resulted in one batch of cocoons. Although general 

 scouting for cactus insects was carried out over a period of several 

 years in southern Arizona, particularly in the Tucson district, no 



