ALFALFA SEED PRODUCTION. 15 



MISCELLANEOUS INSECTS. 



A number of species of small insects visit alfalfa flowers, not for the 

 purpose of getting honey, but to feed upon the pollen and the cellular 

 tissue of the flower. The most common insects of this kind are the 

 thrips. These insects are found in all parts of the United States, and 

 have frequently been abundant in the alfalfa flowers at Arlington 

 farm, Virginia; Chico, Cal.; Pullman, Wash,; and at Chinook and 

 Havre, Mont. At Pullman 1,119 thrips were found on 16 racemes 

 of alfalfa flowers, or an average of 69.9 thrips on the flowers of each 

 raceme. At Havre 48 thrips were found on 13 racemes. These 

 minute insects do not trip the alfalfa flowers. 



In conducting the various experiments described in this paper, 

 it has been observed that even when the thrips are present in very 

 large numbers the flowers very rarely develop into pods and seed 

 unless tripped. On the other hand, when the flowers are tripped, a 

 large proportion usually produce pods and seeds, even though the 

 thrips are very abundant. The evidence at hand indicates that 

 the thrips are neither appreciably beneficial nor injurious in their 

 influence upon the development of alfalfa seed. 



Another insect commonly found on alfalfa flowers is the tarnished 

 plant bug {Lygus pratensis). BHster beetles (Epicauta puncticollis 

 Mannerheim) are found on alfalfa in abundance at Pullman, Wash., 

 feeding on the more tender portions, especially the stamens and style. 

 At Brookings, S. Dak., occurs the related Macrobasis unicolor Kirby. 

 This beetle, according to R. A. Oakley, does considerable damage 

 to the flowers, but incidentaUy trips many. 



EFFECTS ON SEED SETTING OF VISITS OF INSECTS WITHOUT TRIPPING FLOWERS. 



To determine whether or not the visiting of flowers by insects 

 without actual tripping aids in seed setting, observations were made 

 at Chico, Cal., as shown in Table VII. The plants designated as A, 

 B, and C were in full bloom at the time of beginning the experiment, 

 and up to that time were not protected in any way. After counting 

 and tagging the old and young flowers to be observed, the plants 

 were screened with tarlatan netting, with the exception of a portion 

 of plant B, which was left to develop under natural conditions. 



The flowers designated as old flowers were the oldest on the plant 

 not tripped at the time the experiment was started, and many of 

 them probably had been visited one or more times by bees or other 

 insects without tripping. That insects had visited the older flowers 

 is merely assumption, but as many bees and other insects were work- 

 ing the alfalfa flowers on the days immediately preceding the starting 

 of the experiment, this seems probable. The flowers designated as 

 young flowers were not yet in bloom when they were screened. 



