110 U.S. NATIONAL MUSEUM BULLETIN 256 



Where the larvae are abundant, they cause a great amount of 

 damage. Their activity sets up rot condition. Segments, branches, 

 and whole plants fall to the ground where the destruction is completed 

 by succeeding generations of larvae assisted by plant diseases and 

 scavenging insects, mainly syrphid and stratiomyid larvae. At a 

 village near Puebla in March 1927 the prickly pear hedges surrounding 

 cultivation plots were partially destroyed by very great numbers of 

 larvae, while the fields of cultivated prickly pears, comprising young 

 plants mostly, were heavily infested. The inhabitants stated that 

 although hand picking of the adult beetles was practised, it was 

 necessary to replant the plots of prickly pear every few years owing to 

 the depredations of Cactophagus. In June of the same year these people, 

 on being requested to collect adults, brought in 1500 beetles the 

 first morning and 5000 beetles next day. 



Observations on the life history were conducted under cage con- 

 ditions at Piedras Negras, State of Coahuila, in 1926-27 and at 

 Guernavaca, State of Morelos, in 1933-35. During the latter period 

 field studies were carried out around Puebla, Mexico City, and 

 Guernavaca. 



There is an annual generation. The winter period, when little 

 rain falls for 6 months, is spent in the larval stage. Pupation may 

 commence in December, but full-grown larvae predominate in Jan- 

 uary and February, most pupation taking place in March and April. 

 A few adults can be seen in February and March. However, the 

 main emergence awaits the break in the dry period, and beetles appear 

 in numbers from late April until the end of June. It has been found 

 that moistening the cocoons hastens emergence. The adults live for 

 several months, and their numbers continue at a high level from 

 May until September. They were very plentiful around Puebla and 

 Tlaxcala in May 1934. The beetle population decreases after Sep- 

 tember, and very few can be found by the end of November. Under 

 cage conditions at Guernavaca they did not survive later than Decem- 

 ber, but at Piedras Negras the maximum longevity was 12 months. 

 They are able to live for several weeks without nourishment. 



Oviposition commences at the end of May, is general in June, 

 July, and early August, and ceases by the end of August. The eggs 

 may be placed in wounds and feeding punctures but the favoured 

 location is the areole. The female pushes aside the small spines, makes 

 a small hole in the centre of the areole, deposits the eggs, and covers 

 it with a light brown secretion which sets hard; the position of the 

 eggs is not readily detected. The incubation period occupies 12 to 16 

 days. Larvae develop rapidly; many are well grown at the end of 

 August, and most are almost full-grown by September 30. 



