588 FIFTH REPORT OF THE ENTOMOLOGICAL COMMISSION. 



founded, they may be distinguished by the following characters in addition to those 

 of the family Tenthredinid;e to which these insects belong: 



The first, Dolerus arvensis, is a little more than one-third of an inch in length by 

 about one-third as wide, and measures not far from two-thirds of an inch across the 

 extended wings. The head and body are dark steel blue except the thorax, which is 

 variegated with yellow and black. 



67. Dolerus bieolor Beauv. 



Referring to the second species of Dolerus, Forbes continues his 

 account as follows : 



The other species, Dolerus hicolor, is a trifle smaller than the first, brownish yellow 

 except the wings, the head, the middle of the thorax, and the legs, all of which are 

 black. 



Both these insects are abundant everywhere in early spring, and the larvte of both, 

 similar in appearance to green caterpillars, but distinguished by the possession of 

 eleven pairs of legs, feed upon the leaves of the willow a little later in the season. 



Careful watching in the field soon convinced me that these saw-flies were neither 

 biting nor piercing the buds or flowers, but that they were merely licking off the 

 semi-fluid exudation from the surface of the bud scales. Dissecting the specimens 

 and examining the contents of their stomachs with the microscope, I found only a 

 clear fluid, without a trace of solid matter except occasional spheres consisting of 

 clusters of threads of fungous parasites Critically searching the surface of a bud 

 scale which these flies had but just worked over, I saw that no injury whatever had 

 been done to the tissues of the plant, even the slender hairs with which the scales 

 were covered being wholly undisturbed. Watching the flies with a glass, I could 

 see that their biting jaws remained all the time closed, but that their flap-like max- 

 illae were continually employed in mopping up the moisture from the viscid surface, 

 and as they have no mouth-parts capable of piercing the substance of a plant, it was 

 clear that no injury w^as being done. Finally, I confined a lot of the saw-flies in a 

 breeding cage with pear buds not yet open. The insects industriously worked over 

 the surfaces of the unopened buds and even entered the flowers as they expanded, 

 but did neither any visible injury whatever. The buds afterwards all opened out in 

 abundant bloom, and remained fresh for several days, while the poor saw-flies, hav- 

 ing lapped up all the sirup available, starved to death in the midst of the uninjured 

 blossoms, A little experiment showed that they were especially susceptible to th& 

 influence of pyrethrum, and that a single thorough application to a tree would kill 

 all upon it at the time. 



The above brief account of these insects is given merely to set at rest the fears of 

 those who, like my correspondents, may be led to attribute to them serious mischief 

 really due to quite other causes. (Forbes.) 



C8. Nematus ventralia Say. 



The larvae of this saw-fly were found by Dr. Harris on leaves of the 

 willow June 22 ; they spun their cocoons June 24, the flies appearing 

 from July 15 onward. A second brood of these occurred on the nar- 

 row-leafed dwarf willow September 5, and on the same shrub a pair 

 of flies apparently recently transformed. The cocoons were made Sep- 

 tember 20. A swarm of larvae was also found October 17. (Harris' 

 Corr., p. 270.) 



Larva. — Six-tenths inch long, greenish black, and with ten heart-shaped ocher-yel- 

 low spots on each side, beginning on the second ring. Prolegs fourteen ; viz, twelve 

 Tentral and two very short retractile ones to the last ring, all of a whitish color; 

 the first pair on the fifth ring, and the rest (except the anal pair) on the following 



