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Pomona College Journal op Entomology 



off such formidable enemies, unless it be accomplished by keeping away the 

 adult flies and preventing them from depositing their eggs in the colonies. 

 That the species is preyed upon by internal parasites is substantiated by Mr. 

 Davidson, who states that the insect is "much parasitized by an Epliednis." 

 But worse than any insect parasite or predator is a peculiar plague which, in 

 this section, kills off absolutely every colony in certain areas. The insects re- 

 tain their shape until the very last, and as soon as dead simply melt away. If 

 one is touched it immediately falls as a drop of dark brown liquid. The skins 

 of thousands still hang to the former places of lodgment, showing the situa- 

 tions of a once prosperous colony. The contents of one of these melting bodies 

 placed on a slide under a microscope shows thousands of small egg-shaped 

 bodies, each with a small tubercle at one end. Whether these are the resting 

 stages of bacteria, fungui or sporozoans I cannot say, but they are not to be 

 found in the contents of healthy living specimens. 



The attacks en the insects are greatest along the water's edge where the 

 willows are growing in or near damp soil. In such places it is dilScult to find a 

 complete colony, while back from the river there are no evidences of the plague, 

 if so it be. An experiment was made to see if the disease could be communicated 

 to other species of aphids, and accordingly a large number of the diseased 

 colonies of the common Cottonwood Aphid (Thomasia populicola (Thos.) Wil- 

 and liberate the body contents. This mixture was then poured over large 

 colonies of the common Cottonwood Aphid (Thomasia populicola Thos. Wil- 

 son), but none of them have yet succumbed to the disease. Specimens have 

 been sent to the [Jniversity of California to ascertain, if possible, the nature of 

 the malady. , 



The winged forms are exceedingly scarce, but those found carried their 

 wings vertically and not horizontally, as described by Buckton. 



Essigella californicus ( Kssig) Del Guercio 

 (Montcrcv I'iiie Louse) 



1909 Lachnus calif oniicus Essig. 1". C. Jr. Ent., I, pp. 1-4. Original 



description. 

 1909 Essigella californicus (Essig) Del Guercio. Riv. Pathol. Vcg.-Pa- 



via. Anno. Ill, N. 20-21. Formation of a new genus. 

 1!)09 Essigella californicus (E.s.sig) Del Guercio- Baker. I'. ('. .Ir. Ent., 



I, pp. 73-74. Translation of article by Del Guercio. 

 The description of this insect having been my first attempt, and a very 

 poor one, it has been my constant aim to re-draw and re-describe it so as to give 

 it a more substantial place in the literature of the Family Aphidida'. In the 

 original description tlie liody differentiations, esi)ecially of the thorax and 

 abdomen, were omitted in the drawings; the measurements were taken witliout 

 the aid of the camera lucida and tlierefore inaccurate; the text stated tluit the 

 antennae of the winged female was six-articled instead of five, which was a 

 printer's error; so far as I can now tell, there are no sensoria on the legs at all. 



