REVISION MALACOSOMA HUBNER IN NORTH AMERICA 49 



the observation on several occasions that more normal egg masses were 

 obtained than the number of males in the cage. If the males mate only 

 once, there should never be more normal egg masses than there are 

 males, since females do not lay normal egg masses unless they have 

 mated. Williams (1939) states that the females of M. americanum only 

 mate once. This probably is true also for females of the other species of 

 Malacosoma, but was not confirmed during this study. 



Even though most of the oviposition took place the first night, the 

 moths were left in the cage until all of the females had laid egg masses, 

 or until all had died. Whenever possible two or more egg masses were 

 obtained. After oviposition was completed the egg masses were held at 

 80 percent R. H. under the temperature conditions prevailing in the 

 insectary-trailer. In October they were placed in a 10° C. temperature 

 cabinet for a month, and then moved to 5° G. for the rest of the winter. 

 Before hatching the following spring, the spumaline was brushed off and 

 the eggs were surface-disinfected for 2 minutes in 1 -percent sodium 

 hypochlorite to reduce the possibility of having disease problems such as 

 were encountered in the field rearing. No serious disease problems were 

 encountered, although a few of the larvae died showing the typical 

 symptoms caused by the noninclusion virus that caused serious trouble 

 in the insectary-trailer. 



Hatching was accomplished by holding the egg masses at 100 percent 

 R. H. at room temperature. The caterpillars were reared in cages using 

 the same methods already described, with the exception that all of them 

 were fed apple foliage, which they accepted readily with no noticeable 

 adverse effects. 



Only one egg mass from each cross or control was reared, because of 

 the amount of labor involved in rearing them. It would have been 

 desirable to rear several egg masses from each cross and the controls, 

 but it was impossible because of limitations of space and manpower. 



Results 



All attempts at crossing M. disstria, M. constrictum, and M. tigris with 

 each other or with other species were completely unsuccessful. This does 

 not mean that such hybrids cannot be produced, but no field-collected 

 specimens have ever been seen which could be interpreted as being 

 hybrids between these three species or between these and any other 

 species, so it is safe to say that they are completely isolated in the field. 

 M. tigris and M. constrictum are widely separated geographically, too. 

 No difficulties were encountered in obtaining control egg masses of M. 

 tigris or M. constrictum under caged conditions, but the success with M. 

 disstria was quite variable. Nearly 100 percent of the females from Texas 



