﻿226 PROCEEDINGS OF THE NATIONAL MUSEUM vol. lOO 



this group : confusa Lee, -filipes (Walker) , fuUginosa Lee, fuscipleura 

 Lee, latisquatna (Edwards), longipal'pata Lee, papua Brug. In addi- 

 tion to mathesoni^ two other Solomon species fall into this group, 

 namely, stonei and torokinae. These three species cannot be confused 

 with longipal'pata and confusa, since the latter have palpi at least 

 two-thirds as long as the proboscis in the male. T. latisqucuina differs 

 from the Solomon species in the larger number of prescutellar bristles, 

 usually six or seven pairs : fuscvpleura is separated by the extremely 

 short male palpi (less than one-sixth the length of the proboscis) and 

 the proboscis longer than the front femur ; fuUginosa has all the erect 

 occipital scales dark (they are white in the center in mathesoni, stonei, 

 and torokinae) ; T. filipes, as has already been mentioned above, has 

 short hind tibiae. T. papua closely resembles mathesoni and the other 

 Solomon Rachisoura, but, according to Brug's description, can be 

 separated on the basis of the short proboscis of the female, 0.75 of 

 abdomen and 0.9 of front femur, and the longer palpi of the male, 

 about 0.3 of proboscis. 



The larval stage has been described for only four species of this 

 group outside of the Solomons. The obvious differences noted are 

 as follows : longipalpata has the apical spine of the maxilla over twice 

 the length of the body of the maxilla ; fusclpleura is easily separated 

 by the pecten restricted to the basal portion of the siphon; confusa 

 has a simple ventral siphonal valve hair ; filipes can be separated from 

 nnathesoni by the smaller number of comb scales (3 to 5, as compared 

 with 6 to 11). 



T. mathesoni males caimot be confused with those of stonei and 

 torokinae since the apex of the palpus has no specialized bristles and 

 the ninth tergite is very characteristic. The females, on the other 

 hand, cannot be separated always from those of stonei as both usually 

 lack bristles on the apex of the palpus and the amount of white scaling 

 on the posterior pronotum is often difficult to determine exactly. The 

 larvae of nnathesoni differ from those of stonei and torokinae, par- 

 ticularly in the greater development of the pecten teeth, the longer 

 siphon, and the reduction of the dorsal hairs on the abdominal 

 segments. 



No other species of Rachisoura is known to breed in the leaf-axils 

 of species of Colocasia and Alocasia. Apparently mathesoni is re- 

 stricted to this ecological niche, as numerous collections throughout 

 its known range have failed to reveal it in any other habitat. 



Variation. — A study of 12 individual rearings from Guadalcanal 

 shows considerable variation in individuals of this species. In the 

 adults the postnotal bristles are often absent, the spiracular bristles 

 vary from two to four, and the upper sternopleurals are just as fre- 

 quently absent as present, when present being very poorly developed. 



