xxxiii, '22] ENTOMOLOGICAL NEWS 171 



Observations on Two Mealy Bugs, Trionymus trifolii 



Forbes and Pseudococcus maritimus Ehrh. 



(Horn., Coccidae). 



By W. S. HOUGH, State Crop Pest Commission, Winchester, 



Virginia. 



There was a time not long- since when all mealy bugs were 

 thought to he restricted feeders, that is, each species was 

 thought to be limited to a single host plant or at most to very- 

 few. Likewise, a single host plant harbored but one species. 

 With this belief prevalent it is quite natural that when different 

 mealy bugs were found on the same host they were considered 

 different forms of the same species. As a result, cases of sea- 

 sonal forms or seasonal dimorphism appeared in literature 

 from time to time and were not openly questioned until Ferris 

 (1918 a & b) presented evidence that probably all such cases 

 involved two or more species. The history and literature of 

 several typical cases is reviewed by Ferris in the articles re- 

 ferred to. 



The first case of seasonal dimorphism was established by 

 Davis (1894) in connection with his observations on the clover 

 root mealy bug (Trionymus trifolii. Forbes). He observed a 

 "winter form" which was an "oval, plump, mealy, egg-like 

 object" and a "summer form" having "white waxy filaments 

 which project out from the body." Both of these "forms" 

 were studied by the writer at Columbus, Ohio, and were kept 

 under observation from October, 1920. until June, 1921. A 

 summary of the information obtained follows. The study was 

 made under the direction of Dr. Herbert Osborn. (i. F. Fer- 

 ris, of Stanford University, and Harold Morrison, of the 

 Bureau of Entomology, examined specimens of Pscitciococcns 

 maritimus Ehrh., the so-called "summer form." The ants 

 were identified by Dr. W. M. Wheeler. 



Trionymus trifolii Forbes. 



In life the adults vary from 2 mm. to 3 mm. in length, are oval, 

 plump, and when viewed laterally appear somewhat cylindrical. Tin- 

 flesh-colored body is covered 1>y a white wax powder. There is but 

 a single pair of white caudal tassels which usually vary from one-eighth 

 to one-fifth of the length of the ho<ly. TlitM' tassels are frequently 



