THE ALFALFA CATERPILLAR. 
23 
preceding winter may have killed the hibernating Pteromalus larvae 
(fig. 11). In the same year Mr. K. N. Wilson found the species 
quite numerous in the Imperial Valley of California. As many as 20 
per cent of the Eurymus pupae were parasitized by it. 
This parasite seems to be distributed over a considerable area, for, 
besides being present in Arizona and California and, as stated, at 
Wellington, Kans., it has been reared during the season of 1913 and 
found to be quite abundant at Salt Lake City, Utah, by Mr. Rock- 
wood, and at Nashville, Tenn., specimens were raised by Mr. Larri- 
mer from a single pupa of Eurymus. 
It seems almost certain that this parasite winters as a larva with- 
in the pupal shell of the host. The first lot collected in a pupa of 
the alfalfa caterpillar in December were discovered 
as larvae in January and soon thereafter turned to 
pupae (fig. 12), issuing as adults in March. The 
Fig. 11. — Pteromalus 
eurymi: Larva. 
Greatly enlarged. 
(Original.) 
Fig. 12. — Pteromalus 
eurymi: Pupa. 
Greatly enlarged. 
(Original.) 
Fig. 13. — Pteromalus 
eurymi: Adults is- 
suing from chrys- 
alis of alfalfa cat- 
erpillar. Enlarged 
nearly three diam- 
eters. (Original.) 
eggs are laid in pupae of Eurymus, from 40 to 114 parasites develop- 
ing in one pupa. About 80 to 90 per cent of these are females and 
the rest males, and the adults issue from one or more tiny holes in 
the pupa of their host. (See fig. 13.) 
The combined length of the egg^ larval, and pupal stages in the 
warmer weather of August is from 12 to 15 days, while the pupal 
stage was found to cover 4 days in the month of August and 12 
to 15 days in February, the variation being due to differences of 
temperature. Thus several generations are possible each season, and 
thus, with abundant egg production and high percentage of females, 
gives rise to a rapid increase in the number of parasites, so that by 
late August the multiplication of the host species is checked. 
