REVISION MALACOSOMA HUBNER IN NORTH AMERICA 61 



that a certain percent of the sperm were inviable. In both R27 and 

 R36, however, the infertile eggs (27% in R27 and 22% in R36) were 

 more or less evenly scattered throughout the egg mass, indicating that 

 some of the eggs or sperm probably were inviable for some reason, since 

 only 4 percent of the eggs of the lutescens control were infertile, and 

 only 6 percent of the eggs of the pluviale control were infertile. In other 

 respects, such as date of hatching, percent survival after hatching, 

 average number of days from hatching to emergence of adults, and 

 sex ratio, tliere are no striking differences between R27, R36, and 

 their reciprocals. 



The differences between the controls (R29 and R30) in regard to 

 date of hatching and length of developmental period from hatching to 

 emergence as adults are of interest and possibly of some significance. 

 The Ggg mass of the bog pluviale hatched on April 30, while that of 

 lutescens hatched on May 3d. The hog pluviale averaged 34,5 days from 

 hatching to adult emergence under greenhouse conditions, while the 

 lutescens averaged 39.2 days. There is a possibility that this difference 

 of about 5 days could be due to temperature differences at various 

 locations in the greenhouse, disease, and the other factors already 

 discussed which could influence developmental rates, rather than to 

 any real difference in developmental rates. It also could be due to 

 chance, since nonbog pluviale from Port Angeles, Washington, (R18) 

 hatched on May 2d, and averaged 38.9 days from hatching to emer- 

 gence. It may be also that the hatching date is actually earlier, and 

 the developmental rate of the bog pluviale under given conditions is 

 faster than that of nonbog populations. If this is true, it could account 

 for the obse.-ved differences in developmental rates between the bog 

 population oi pluviale (R29) and the nonbog population (RIB) when 

 reared at similar temperatures. If the bog and nonbog populations 

 occurred in the same locality, however, and they are not known to do so 

 at the present time, any seasonal isolation due to differences in adult 

 emergence times would tend to be cancelled out by the faster develop- 

 mental rate of the bog population. In other words, the bog population 

 would keep pace with the nonbog population because their rate of 

 development under cooler conditions in the bog would be about the 

 same as the nonbog population under warmer conditions. 



If the difference in developmental rates between bog pluviale and 

 lutescens is real, when it is combined with the 3-day difference in hatch- 

 ing dates, it results in the adults of bog pluviale emerging approximately 

 1 week earlier on the average than those of lutescens. Since the nonbog 

 populations of pluviale, however, are most likely to be the ones that 

 occur in the same locality as lutescens^ it does not appear that there 

 would be anv seasonal isolation between pluviale and lutescens. It was 



