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 1 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 ofisoleta, etc 28 



Rotten from intestinal disease 3? 



Infested by tachinid parasites 6 



Alive and healthy 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 pupse 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 Ewrymus eurytheme was found. This is 

 the very common Trichogramma 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. 



