REVISION MALACOSOMA HUBNER IN NORTH AMERICA 147 



of Ceanothus in most areas where it was found. For example, Ceanothus 

 thyrsijlorus, a preferred host of c. ambisimile, was never found where 

 c. californicum was found. 



The failure of c. ambisimile and c. californicum to overlap could be due 

 to one of two opposite reasons as suggested by Mayr, Linsley and 

 Usinger (1953). First, the zone of contact may connect two very differ- 

 ent ecological areas, which certainly does not appear to be the case in 

 the Los Altos area. Secondly, the ecological requirements may be so 

 similar in every respect that the two populations compete with each 

 other, with c. ambisimile slightly superior on its side, and with c. cali- 

 fornicum superior on the other side. They are indeed quite similar in 

 many respects, but if it is true that c. ambisimile does not prefer Q_. agri- 

 folia and c. californicum does prefer it (all the evidence indicates this), 

 there appears to be no reason why c. californicum should not occur in the 

 same area as c. ambisimile, since Q,- agrifolia grows commonly in the area 

 and competition would be practically nonexistent on Q^. agrifolia. 

 There would be some competition on other hosts such as willows and 

 fruit trees, but this should not be severe enough to prevent their occu- 

 pation of the same geographical area. It can only be concluded that 

 such a situation is prevented by complete interbreeding and intergra- 

 dation of c. ambisimile with c. californicum wherever their distributions 

 meet. 



It is possible that c. ambisimile occupied a very restricted area in the 

 Santa Cruz Mountains before the arrival of settlers, and that only rela- 

 tively recently has it come into contact with c. californicum after the 

 planting of fruit trees throughout much of the area. Even if this is true, 

 however, it is obvious that c. ambisimile has not been separated from c. 

 californicum long enough in the past for the development of isolating 

 mechanisms which would permit coexistence in the same area. There- 

 fore, c. ambisimile is regarded as a subspecies because this most accurately 

 represents its relationships to the adjacent populations as far as they 

 are known. 



Specimens Examined. — 333 (Museum specimens — 69 males, 42 females, 

 50 larvae; reared specimens — 89 males, 83 females, plus numerous larvae 

 and egg masses). See Appendix I for data on collections made during this 

 study, and for data on collections of intermediates between M. californicum 

 ambisimile and M. Californicum californicum (page 271). 



California. — Mountains back of Alma (Santa Clara Co.); Ben Lomond 

 Ridge (Santa Cruz Co.); Big Basin; 3 mi. SE. Big Basin; Big Basin Redwoods 

 State Park; Carmel; 1 mi. N. Holy City; La Honda Road (San Mateo Co.), 

 Las Uvas Cr.; Los Gatos; Monterey Co.; Mt. Madonna Co. Park (Santa 

 Clara Co.); 3 mi. E. Mt. Madonna Co. Park; Santa Clara Co.; Santa Cruz; 

 Santa Cruz Mtns.; Saratoga; 5 mi. W. Saratoga; Silver Creek Hills (Santa 



