April, '15] McCONNELL; UNIQUE TYPE OF INSECT INJURY 261 



the parasite was about the same in all parts of Kansas under various 

 atmospheric and soil conditions. About 16 per cent of the eggs 

 collected in the field were parasitized. This year 14 per cent of the 

 eggs collected in the field outside of Manhattan were parasitized. 



President H. T. Fernald: The next paper on the program will 

 be read by Mr. W. R. McConnell. 



A UNIQUE TYPE OF INSECT INJURY 



By W. R. McConnell, Bureau of Entomology. 



Introduction 



The bean-leaf beetle, Cerotoma trifurcata Forst., is well-known in 

 the south as an enemy of beans and cowpeas. It is known chiefly 

 from the damage done by the adults to the foliage of these hosts, 

 where its injury may consist merely of eating rounded holes in the 

 leaves or may extend to the total destruction, particularly of young 

 plants. 



The first record of a food plant was made in 1877 by Professor 

 E. A. Popenoe^ w^ho found the beetles damaging the leaves of garden 

 beans in Kansas. In 1887, Professor F. M. Webster ^ recorded the 

 total destruction of garden beans in Louisiana and Indiana. He also 

 found cowpeas seriously damaged in Louisiana and predicted that 

 ''To the cowpea this may prove a formidable enemy, especially in 

 the south." Popenoe later published a more complete account^ 

 and Dr. Chittenden^, ^ has published several important papers on 

 this insect, giving notes upon several additional food plants, upon its 

 life history, and recording injurious outbreaks as far north as New 

 Jersey. A few other writers, particularly H. E. Weed,^ have added 

 important facts regarding this insect. 



The larvse have been described a number of times as feeding on the 

 roots, channeling furrows in the bark of the subterranean portion of 

 the stem, and even as burrowing up through the stem. While all 

 these forms of injury may take place, it is evident that they are not 

 sufficient to account for all the phenomena of the distribution and 

 extent of damage in bean and pea fields. 



In the fall of 1912, Mr. T. H. Parks, formerly of the Bureau of 

 Entomology, and the writer, while working in the lower Mississippi 

 Valley, discovered that the nodules on the roots of cowpeas had been 

 damaged by larvae resembling those of Diahrotica. Adults of the 

 bean-leaf beetle were feeding upon the foliage and we suspected that 

 the larvae might belong to this species. The unique character of this 

 injury led us to believe that a careful study of these larvse in relation 



