THE ALFALFA CATERPILLAR. 19 
were dried up, but now, in the thrifty-growing alfalfa fields of this 
once arid country, it finds a place to continue its activity throughout 
the summer, and, as has been mentioned before, it is this very change 
that has enabled the species to become the pest that it is to-day. 
NATURAL CHECKS TO THE SPECIES. 
Were it not for the fact that this species is preyed upon by a great 
many natural enemies it would indeed prove a much more serious pest 
than it is at the present time. Parasites and predaceous insects, 
fungous and bacterial diseases, birds, toads, and even domestic fowls, 
all play a large part toward keeping the species well within bounds 
during certain seasons of the year. 
In 1889 Scudder x said : " Strange to say, not a single parasite 
has been reported to attack this common insect." However, the au- 
thor and others, during the past three years, have reared as many as 
nine parasites from the various stages of this butterfly, and some 
of these at times are quite numerous. An example of the extent of 
parasitism may be gleaned from the following record of a collection 
of 154 pupse made at Tempe, Ariz., on August 26, 1912 : 
No. of 
pupae, 
Infested by chalcid parasites 82 
Partially eaten by Heliothis absoleta, etc 28 
Rotten from intestinal disease 37 
Infested by tacbinid parasites 6 
Alive and bealtby 1 
Total : 154 
This, of course, was an exceptional collection, but often collec- 
tions were made from which as few as 5 per cent of the pupae were 
reared to adults. The percentage of parasitism usually reaches the 
maximum during the month of August, so that rarely is much dam- 
age done by the caterpillar after that time. 
PARASITES OF THE EGGS. 
Only one egg parasite of Eurymus eury theme was found. This is 
the very common Trickogramma minutum Riley (fig. 7), which is 
known as an egg parasite of a great many species of insects. In its 
relation to eggs of this species it was first found by Mr. Harry New- 
ton, of the Bureau of Entomology, who was working at Tempe, 
Ariz., during the summer of 1913. On July 26 he found three eggs 
which were very dark in color, and two days later three of the tiny 
parasites issued from one of these. Two days previous to Mr. New- 
ton's collection Mr. T. Scott Wilson collected 100 eggs. From three 
1 Scudder, S. H. The Butterflies of the Eastern United States and Canada, v. 2, Cam- 
bridge, 1889, p. 1132. 
