CACTUS-FEEDING INSECTS AND MITES 117 



San Luis Potosi and 0. hyptiacantha at Tehuacan and Oaxaca. In 

 Australian experiments the fruit of the shrub pears 0. inermis and 

 0. stricta proved suitable to the insect. 



Although Opuntia imbricata and other forms are widespread from 

 western Texas to Arizona and in northern Mexico, reports of midge 

 infestation of Cylindropuntias have been obtained from one locality 

 only. In March 1927 infested fruit of 0. imbricata were quite common 

 near Aguascalientes, Mexico, but no attack was observed among the 

 various kinds of Platyopuntias in the vicinity. In March 1928 0. 

 imbricata fruit were infested over an extensive area in the same locality; 

 again, no sign of injury to fruit of the several species of prickly pear 

 could be traced. From imbricata material brought to Uvalde, Texas, 

 the adult midges that emerged oviposited readily in fruit of the prickly 

 pear, 0. lindheimeri. 



Although the slender-jointed 0. leptocaulis has been recorded as 

 a host plant on a few occasions, it is evident that its fruit are rarely 

 selected. In March 1928 two plants with infested fruit were found in 

 the Uvalde district. In October 1929 attacked fruit were observed on 

 a few plants at Aguascalientes and San Luis Potosi, Mexico. 



The life history of A. opuntiae is peculiarly adapted to its host. There 

 is one generation annually. The midges emerge in the early spring 

 when the prickly pear plants are producing new growth and flower 

 buds. The females select for oviposition buds from 2 to 7 days old 

 and usually less than one-half inch in length; these buds bear small 

 leaflets and have reached a stage where there is an air space in the 

 ovary and the flower style has not yet appeared. The attacked buds 

 develop into normal flowers. About four weeks after the eggs have 

 been laid, the result of the infection is indicated by a slight but definite 

 yellowing of the young fruit. The seeds do not develop but remain 

 soft and partially formed. The fruit remains green-yellow throughout 

 the summer and does not ripen. Very small yellow or orange larvae 

 are found among, but not in, the seeds. Their growth is very gradual 

 and is hardly perceptible to the eye until December. In the mid- 

 winter months of December and January, the larvae become more 

 active, but they are still quite small in early February. They then 

 grow rapidly, pupate in late February and March, and emerge as 

 adults in March and April. These observations apply to conditions 

 in Texas and Mexico; in northern Arizona and in Colorado, emer- 

 gence occurs in May and June. For the whole period of their existence 

 the larvae feed among the seeds and do not attack the fleshy parts of 

 the fruit; they pupate in the seed cavity. When ready to emerge, 

 the pupae work their way through the flesh and project through the 

 sides of the fruit. Shortly after emergence of the adults the fruit shrivels 



