128 PROCEEDINGS ENTOMOLOGICAL SOCIETY 



AN INTERESTING CASE OE ANTENNAL ANTIGENY IN 



THYSANOPTERA. 



BY J. DOUGLAS HOOD, United States Biological Survey. 



Sexual differences of both color and structure are very com- 

 mon in Thysaiioptera. Usually these differences are minor, 

 but they can no doubt be detected in every species. Occasionally 

 the antigeny produces a dissemblance in habitus which in a few 

 instances has led to the assignment of the sexes to different species 

 or even genera. The dimorphism may appear in any part of the 

 body. It concerns the form of the head in Trichothrips flavi- 

 cauda; the size, form and armature of the three distal segments 

 of the fore legs in nearly all species of Tubulifera; the size and 

 structure of the prothorax, particularly in the Phlceothripidse ; 

 the armature of the pterothorax in the genus Dinothrips and 

 of the abdomen in Kakothrips and the Megathripida? ; as well 

 as affecting in numerous ways several other parts of the body of 

 various species. Thus, ocelli and wings are wanting in the males 

 of Chirothrips and Limothrips; and in the males of most Thripoidea 

 the abdominal sternites have pale sensory areas of constant form 

 and arrangement. Frequently, too, the color of the male is 

 radically different from that of the female. 



The antenna, however, are usually very stable, differing but 

 little with sex, among individuals, or even in different species 

 of the same genus. Many genera are separated on the strength 

 of such characters; and recently a new family has been erected 

 for two European species whose antennae depart distinctly from 

 the general plan of the group to which they belong. 



The occurence in the United States of a species whose female 

 has antennae of normal form and structure but whose male has 

 these organs so modified through the reduction in size of certain 

 segments, the increase in size of others, and the multiplication 

 of sensory hairs of their surface, must thus be of importance in 

 its effect upon our conceptions of generic characters. While 

 such sexual anomalies should perhaps not in themselves be made 

 the basis for the separation of new genera, they nevertheless 

 point to a probable difference in phylogeny and lead to a search 

 for correspondingly important characters in the opposite sex. 

 In the case of this species such characters are found in the form 

 of the head, the position of the anterior ocellus, the^ proportionate 

 lengths of the antennal segments, the narrowed p'rothorax, and 

 the vestigial condition of the ovipositor. It is thus proposed to 

 remove Thrips perplexus (Beach) from the genus Thrips and to 

 erect for it the new genus described below. 



