REVISION OF MOTHS OF PRODOXINAE 59 



to the host plants' distribution), but, for the present, it is difficult to 

 relate, largely due to insufficient host information. 



Variation in the development of the maxillary tentacles was first 

 reported by Busck (1947), who consequently synonymized Prodoxus 

 intermedins, a moth formerly thought to be distinct from T. yuccasella 

 because the females lacked tentacles. The abortion frequency of the 

 tentacles appears somewhat comparable to the length character of the 

 male genitalia in that marked popidation differences are to be noted. 

 As shown in table 3, the failure for the maxillary tentacles to develop 

 may be a more common occurrence than previously realized. Two 

 populations of adequate size (nos. 13 and 14) showed no tentacle 

 reduction, whereas populations 6 and 8 demonstrated varying degrees 

 of abnormalcy. The series from Gran Quivira National Monument, 

 N. Mex., contained far more abnormal females (71%) than normal; 

 56 females were examined and 40 were found to have the tentacles 

 either greatly reduced or absent. Usually if these structures are 

 aborted, they are either completely absent or represented by minute 

 stubs, barely visible under low magnffication. In a few specimens, 

 the tentacles were more developed (fig. 32) but stUl considerably 

 reduced in size. In none of these females did the vestigial organs 

 exceed one-third their normal length. 



It is usually characteristic (with some exceptions) for field-captm-ed 

 females possessing fully developed tentacles to show some evidence of 

 pollen beneath the head (fig. 31). For example, in the Gran Quiv^ira 

 population studied, aU normal females (16) carried large masses of 

 poUen in this position. However, no trace of pollen was found on 

 any abnormal specimens, which suggests not only were the females 

 incapable of collecting pollen, but also, that they had made no at- 

 tempts to do so. Thus, it may be possible that the general behavior 

 of these moths diverges from the normal pattern. This is not to 

 imply necessarily that fertility barriers of some kind have evolved, 

 for the frequency of abnormal females in the Gran Quivira popula- 

 tion has attained a high level. This frequency may not be the 

 result of some factor which is maintained within the population at a 

 certain level, or that has increased over a period of time; instead, it 

 may represent a ratio that fluctuates considerably from one year 

 (or brood) to the next. It would seem that females incapable of 

 pollinating the yucca flower and, thus, incapable of insuring a food 

 supply for their progeny, would in time be selected against, especially 

 if it were possible for the number of such females to comprise even- 

 tually a large portion of the population. It should be emphasized, 

 of course, that one normal female is capable of pollinating numerous 

 flowers, and, therefore, able to support the existence of several ab- 



