6 BULLETIN 1363, U. S. DEPARTMENT OF AGRICULTURE 



a great extent due to the abundance of its hibernating hosts. 3 With 

 two exceptions {Schizura concinna and S. unicornis) , these host in- 

 sects pass the winter in the pupal stage either above or below the 

 surface of the earth. The majority of the species are solitary, 

 although a few are gregarious, such as Hyphantria cunea, Euchae- 

 tias egle, and S. concinna, colonies of which are usually found each 

 year in some locality or other. 



Arsilonche albovenosa, Diacrisia virginica, Mamestra picta, and 

 Pontia rapae. although not strictly gregarious, are often found in 

 large numbers. This is particularly true of P. rapae. Probably no 

 native species has been received in such numbers and from so many 

 localities as this insect. As a hibernating host its status is doubtful. 

 Occasionally a fly or two is reared, but considering the hundreds of 

 overwintering chrysalids, the percentage of parasitism is negligible. 



Ampelophaga myron feeds on Virginia creeper and grape; it is 

 solitary and is usually found in small numbers. This species is con- 

 sidered common, although none had ever been received by the writers 

 until 1920. It is single-brooded and hibernates as a pupa, and al- 

 though the collections of this year were heavily parasitized by 

 Apanteles congregatus Say, only a single specimen of Compsilura 

 was recovered from overwintering material. 



Paonias myops, solitary usually but sometimes found in consider- 

 able numbers on wild black cherry, appears to be of little conse- 

 quence as a winter host. In the collections Trogus spp. (brullei 

 Prov. and canadensis Prov.) and Apanteles smerinthi Riley assume 

 prime importance as natural checks. 



Sphinx gordius, of the same general habits as Paonms myops but 

 with a more varied list of food plants, occupies about the same host 

 status. 



Diawnsia virginica is without doubt the most favored overwinter- 

 ing host yet recorded. It is common; a specimen is frequently 

 found here and there and sometimes in the most unexpected places; 

 still it has never been received in abundance. 



So much difficulty has been experienced in the rearing of Mamestra 

 picta that the records are far from complete. The larvae are 

 gregarious in the first three stages at least, after which they disperse. 

 The species seems particularly subject to disease and the hibernating 

 pupae nearly always succumb. If disease is as prevalent in the field 

 as it is in the trays, the chances are slight of its being of much im- 

 portance as an overwintering host. 



Callosamia promethea has been abundantly received from Rhode 

 Island and Connecticut as cocoons and only upon a few occasions 



3 That a higher percentage of parasitism upon the gipsy moth could be reached iD an 

 area where there is a mixed infestation of gipsy and brown-tail moths is not borne out by 

 the parasite records. A careful study of these records over a series of years when one or 

 both of the species were present indicates that a very small percentage of the flies issuing 

 from the brown-tail moth are able to attack the gipsy moth. The few that do must 

 necessarily prey upon larvae of the last stage and here success would not be at all certain. 

 It is doubtful, even though a considerable number of this first generation attacked the 

 gipsy moth, whether their presence could offset the lost efficiency of the parent fly caused 

 by the drain on its reproductive capacity in its attack upon the brown-tail moth. Accord- 

 ing to Culver (2, p. 9), all that can be expected of Compsilura is an average progeny of 

 about 100. Naturally, in a mixed infestation, the parasite would attack the first host 

 that made its appearance. This would be the brown-tail moth. Finding the larvre abun- 

 dant and favorable, it would prey upon this host until tbe appearance of the gipsy-moth 

 larvae two weeks or so later. By this time its reproductive capacity would have been 

 reduced by the extent of its attack upon the brown-tail moth, and consequently it would 

 be less effective against the gipsy-moth larvae. 



