SPECIFIC CHARACTERS USED IN THE GENUS 



PSEUDOCOCCUS. 



By P. E. Smith, 

 Entomological Laboratory of Cornell University. 



INTRODUCTION. 



The purpose of this investigation was to determine the 

 value of the specific characters used in the descriptions of 

 species of Pseudococcus. While all characters used have 

 probably not been noted and while some of those omitted may 

 be of considerable value still the more common and important 

 characters have received attention. 



The investigation has been limited to five species,* namely: 

 agrifoliae Essig, citri Risso, crawii Coq., longispinus Targ., and 

 obscurus Essig. A large number of individuals in each species 

 has been used giving a comparative study for specific variation. 



The writer wishes to thank Professor Alex. D. MacGillivray 

 for the many invaluable suggestions given. 



TABULATION AND STUDY OF CHARACTERS. 



An examination of the descriptions of species in this genus 

 shows a great similarity in the characters used. Provided that 

 these characters do not vary beyond certain limits, this would 

 make the identification of the species easier. However, if these 

 characters vary to any great extent and overlap and merge 

 into each other, the adherence by systematists to these char- 

 acters instead of the introduction of new ones is unfortunate, 

 and would make the identification of species very difficult, if 

 not impossible. In that case the most valuable data in the 

 descriptions would be the locality and host-plant data. 



Body. 1. Size. -In the great majority of descriptions, the 

 length and width of the body is given. In the measurements 

 given, a great variation in the length of each species is noted. f 

 Lengths such as 3-4 mm., 2-5 mm., 1.5-4 mm., are very fre- 

 quent, showing the wide variation noted by those describing 

 species. The tablesj showing the lengths of the body, (Tables 

 1, 2, 3, 4, 5) in the five species studied do not show a variation 

 any greater than this. A variation of from one and one-half 



* The writer does not express an opinion upon the validity of these species, 

 t R. Mathewson. Can. Entom. XXXIX, p. 286. 



t In these and the following tables an ocular micrometer with a 2-5 and 1-8 

 inch objective were used. All measurements are given in microns. 



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