8 U. S. NATIONAL MUSEUM BULLETIN 2 1 6 part s 



the median and postraedian flagellar segments, and usually have a 

 white median band (a ruptive color mark). 



Oviposition is usually through the cocoon wall. The host pupa or pre- 

 pupa is stung and usually killed or immobilized, and the egg laid exter- 

 nally. Normally there is one parasite per host but in a few groups 

 gregarious parasitism is common. The rather uniform host rela- 

 tionship in the subfamily results in an ovipositor of rather uniform 

 length, which in most species is somewhat over half the length of the 

 abdomen. The species parasitic on borers, however, often have it 

 longer, and the few that oviposit into larvae about to pupate in- 

 stead of into cocoons (as in Atractodes) have it very short. 



Males seem to search for females mostly by flying. Their flight 

 usually has a dancing quality. Their antennae are longer than in 

 females, more slender apically, less flexible, usually without a white 

 band, and with sensory endings rather uniformly distributed. In 

 most species there is a raised sensory area (tyloid) on the outer side of 

 several of the postmedian flagellar segments. 



Experimental biological data under natural conditions is almost 

 nonexistent, but judging from field observations and dates of col- 

 lections it seems safe to make the following generalizations for the 

 subfamily: There are one or more generations per season. Males 

 emerge on the average a little before females, mate with newly emerged 

 females, and are somewhat shorter lived than females. Females, at 

 least, are usually long-lived. Except for accidents or during dry 

 weather, they live from emergence till near the end of the growing 

 season. As a result, males are more common than females in the 

 earlier part of the growing season, females more common near the end. 

 Attrition is rather severe during the dry spells of midsummer, but 

 for many species there is resurgence during the wetter, cooler weather 

 that, at least in the eastern half of North America, usually comes 

 with late summer. Final disappearance for the season begins with 

 the autumnal hardening and drying of vegetation, and is accelerated 

 by progressively harder frosts. A few species with a single generation 

 per season appear in spring and disappear by mid-summer, but most 

 are to be found through the growing season. Some, especially the 

 species parasitic on borers, have a definite peak of abundance in late 

 spring and early summer and a secondary peak during the damp part 

 of early fall. In the West, in areas where there is little summer rain, 

 most species are scarce by late summer, but in the part of the South- 

 west where late summer rains are the rule, mesostenines are more 

 common then. Overwintering is usually in the host cocoon. 



As usual with ichneumonids, adults take dew or rainwater from 

 foliage regularly, feast at honeydew and extrafloral nectaries when 

 these are available, and a few species (such as Acroricnus) regularly 



