48 



U.S. NATIONAL MUSEUM BULLETIN 255 



Map 5. — Distribution of two major growtli forms of Yucca whipplei (modiiieJ from Haines. 

 1941) (stippled area [a]= range of caespitosa group; lined area [b]= range oitypica group). 



whipplei, whereas the range of T. m. extranea corresponds very closely 

 with that of the "typica" group. 



The biological relationships of the two subspecies of Tegeticula 

 maculata have barely been touched upon. Thus, several mteresting 

 problems remain to be investigated which could provide not only a 

 great deal of information concerning the particular relationship 

 treated here, but also of the phenomenon of geographical melanism in 

 general. For example, it would be very enlightening to know what 

 degree of fertility exists between the two forms of T. macidata, as well 

 as to know the phenotypical characteristics of any possible hybrids. 

 Also, studies similar to those conducted by Kettlewell (1961 b, c) and 

 Kettlewell and Berry (1961) should be carried out to determine what 

 possible advantages are present that enable the melanic subspecies to 

 occupy a different range — if, in fact, such is verified. The above 

 authors have discovered that bird predatism and temperature factors, 

 especially in association with the flight time of the adults, provide 

 selective advantages for melanic forms under certain conditions. 

 These explanations, however, do not seem to be correlated with what 



