140 



WILLOW BARK-LOUSE. 



THE WILLOW BAKK-LOUSE. 



( Mytilaspis salicis, n. sp. ) 

 Order of HOMOPTERA. Family of Coccid^. 



On the 8th of May, 1870, I received from Stark 

 county, some twigs of the gray willow, densely in- 

 fested with a pure white bark-louse scale, of about 

 the same size as the Oyster-shell Bark-louse of the 

 apple tree, being about one-tenth of an inch in length, 

 but of a more regularly oblong, oval shape, and ex- 

 hibiting but little of the curved or muscle shell form, 

 which gives the scientific name to this genus of Coc- 

 cidce, and resembling more nearly, both in form and 

 color, the scales of the bark-louse of the pine. They 

 also resemble this last species in having blood-red 

 eggs. The number of eggs under each scale averages 

 about seventy-five, exceeding in this respect those of 

 the apple tree, which usually have about forty-five or 

 fifty, and still more those of the pine which rarely exceed thirty. 



The eggs were just hatching at the time of their reception. The 

 young, like the eggs, are deep-red. Indeed, it is the young within the 

 transparent shell which gives to the egg its color. They exhibit, un- 

 der the microscope, all the characters of the young of the other spe- 

 cies ©f the genus Mytilaspis, being of an oval form, with short, taper- 

 ing, divergent antennae, and two anal filaments, as long as the body, 

 but BO fine at the extremity that the terminal third is only visible un- 

 der a strong magnifier. The four digituli,. or little finger-like proces- 

 ses with which the feet of this family of insects terminate, are very 

 distinct in this species. 



As the minute lice were just hatching at the time of their reception, 

 I tried the experiment of tying one of the infested twigs to a branch of 

 the gray willow, taking pains to adjust it so that the young insects 

 could easily pass on to the tree. For some reason the experiment 

 failed. I could never find the least trace of the insects upon the tree 

 to which they were attached, and yet they were transferred to precisely 

 the same kind of tree as that from which they were taken, and in not 

 far from the same latitude. This failure may, therefore, teach us a 

 useful caution against hasty conclusions in our experiments of trans- 

 fering such minute insects from one kind of a tree to another. The 

 failure of the experiment does not necessarily imply that the insects 

 perish from incongeniality of food. 



The twig from which the figure was taken, was much less densely 

 inftatod with icales than some of the others. 



