ENTOMOLOGY 207 



ing such person and of promptly obtaining information as to the 

 first appearance of the pest in any locality that this circular is pub- 

 lished. (U. S. D. A. B. E. Cir. 137.) 



The Alfalfa Caterpillar. The insect under consideration in 

 this circular is the caterpillar of one of our most beautiful and com- 

 mon butterflies, belonging to the group known as the yellows, and is 

 closely related to the well-known cabbage butterfly. The name yel- 

 lows at once gives one an idea of the appearance of the adult, but 

 this may be misleading, the coloration varying from a bright yel- 

 low (very frequently noticed), through an orange-sulphur (the 

 most commonly noticed), to a pale white (the least often noticed). 

 For some years past the green caterpillars of this butterfly have 

 been reported from various localities in the southwestern United 

 States as feeding on and in some cases doing a large amount of dam- 

 age to growing alfalfa. It should be mentioned here that it is the 

 caterpillar or worm stage of this species that does the damage, and 

 not the adult butterfly. The latter feeds on the nectar of the bloom 

 and in no way injures the plant. In fact, the writer has noticed 

 these butterflies to all appearances springing the pollen triggers on 

 the alfalfa blossoms while feeding, thus, should his observations 

 prove correct, benefiting the plant for seed production. 



It is on ranches and fields from which successive crops of hay 

 are taken that the height of the damage is reached. In such fields 

 the conditions for the development of the species are as nearly ideal 

 as possible, and here the worms are ordinarily unmolested in their 

 feeding and growth. The period elapsing from the time that one 

 crop is cut until another is ready to harvest so nearly coincides with 

 the length of the period necessary for the development of any one 

 generation of the butterfly that the cutting of the hay, as ordinarily 

 carried on, does not reduce their numbers or disturb their work, 

 since the worm -will likely be in the advanced stage or, perhaps, 

 have passed into the pupal stage before the crop is cut off. 



Many fields observed were attacked in strips or patches. Some- 

 times one border would be almost totally devoured, while an adjoin- 

 ing plot would not be molested. Again, in other fields irregular 

 patches would be attacked and the rest of the field not materially 

 injured. In cases where whole borders of alfalfa were injured, the 

 time and amount of water applied in irrigating produced an un- 

 even growth, and as the generation of butterflies, on issuing, chose 

 for egg-laying the strip that was the greenest and freshest, this strip 

 would be the one damaged. It seems possible to account for the ir- 

 regular patches in the same way that is, considering that these 

 patches were ones that -were held back because of the condition of 

 the soil. The soil conditions in one part of the field may be quite 

 different from those in another part of the same field, and thus a 

 varying growth of the crop results, which would be attacked in 

 patches. (U. S. D. A., B. E. Cir. 133.) 



Do not abandon a field because the caterpillars are 'beginning 

 to damage a hay crop. If the caterpillars threaten the destruction 

 of a crop of alfalfa before the hay can possibly mature, mow it at 



