CACTUS-FEEDING INSECTS AND MITES 81 



The eggs are circular and flattened, and are deposited singly on the 

 surface of the segments. The yellowish-white larvae attack the very 

 young cladodes, living beneath a light web, under the protection of 

 which tliey tunnel in and out of the growth. The species is not truly 

 gregarious, but as a rule from two to several larvae occur on the same 

 segment. The flat cocoon, of firm paper-like texture, is attached to 

 destroyed segments, fallen leaves, and other debris. 



The main observations on the life history were carried out at Browns- 

 ville, Texas. It was found that there are between seven and nine 

 generations annually, the actual number depending on climatic con- 

 ditions and on the availability of young growth, since the larvae are 

 unable to subsist on older segments. Between March and August the 

 life cycle of each generation averaged 28 to 35 days; the shortest 

 recorded life cycle was 21 days. In the autumn months of September 

 to November, development was slower. The majority of the last 

 autumn generation pupated in November and remained in the pupal 

 stage until late February or early March, when the adults emerged 

 in numbers. Sporadic moth emergence and oviposition may take 

 place during winter. Thus, in 1932-33 moths emerged and oviposited 

 from November 22 to December 11, and young larvae were seen 

 throughout December; presence of a few of young larvae in the field 

 in early February indicated that some adults had emerged in late 

 January; these larvae died during a period of cold weather in the 

 middle of February. 



Adults have remained alive for 12 to 20 days, feeding readily on 

 sweetened water. During the period March to July, the incubation 

 period occupied 3 to 5 days, the larval period 10 to 16 days and the 

 prepupal and pupal period 7 to 16 days. 



Around Brownsville and in coastal areas of Tamaulipas the larvae 

 are often very abundant from April to June, which is the main growing 

 season for 0. lindheimeri. Under favorable climatic and nutritional 

 conditions the species is capable of rapid increase, but in the autumn 

 months the essential young growth is scarce and the population dwindles 

 to small numbers surviving in localized areas. It has been found 

 possible to bring about an increase in the infestation in the late summer 

 and autumn by cutting back the Opuntia plants, and thereby inducing 

 the production of new shoots. Owing to the rapid decay and destiiic- 

 tion of the attacked young growth, starvation causes heavy mortality 

 among the larvae. Little information has been obtained on the fe- 

 cundity, but it is known that individual females can deposit at least 

 50 eggs. In rearing operations the difficulty of maintaining an adequate 

 supply of very young growth has been a serious factor in limiting 

 the increase; on one occasion 1500 adults were reared from 160 parents. 



263-417—68 7 



