54 FROGHOPPER BLIGHT OF SUGAR-CANE. 



It is of some importance to decide whether the insect is native to 

 these islands or is an introduced pest. Kersha\v (1913 C. p. 8) considered 

 that it was indigenous to Trinidad for tlie following reasons : — 



" (1.) There are at least four species of the genus in the island. 



" (2.) It prefers various native grasses as food plants to canes. 



'' (3.) It has at least two egg parasites and the nymphs are killed 

 off to some extent by the larvae of native Hover-flies (Syrphidae.) 



"(4.) There are very commonlj' one or two large parasitic worms in 

 the abdominal cavity among the viscera of the adult frog- 

 hopper, and these worms also occur in other Homoptera here." 



On the other hand in a letter written in August 1916 Mr. Kershaw 

 suggests that I should search for parasites in Argentina "because of 

 rumours of much forage Ijrought thence to Trinidad some 30-40 years 

 ago," which would imply that he still thinks it possible that the insect 

 might have been introduced with the grass from that country. 



Urich (1910 C. p. 4) says that there i-s no doubt that it is indigenous 

 to Trinidad, but gives no evidence in support. 



If it should be an introduced pest it must have been here at least 

 £fty years {see Section III.) but in addition to the arguments for its 

 being native given by Kershaw''' we now know that there are closely 

 related species in the various surrounding countries. Tobago has T. 

 carmodyi, British Guiana has a species very closely related to T. 

 carmodyi in the North-West-District and T. Jiavilatera on the Demerara 

 and Esseqnibo coasts. At La Guayra, Venezuela, I found yet another 

 closely related species, Toinaspia propinqiia Walker, and others occur 

 at intervals of a few hundred miles along the coast. 



It seems to be the rule rather than the exception in Central Amei'ica 

 for the species of the genus Tomaspis to have a range limited to a few 

 hundred miles at most. 



In view of these facts it is difficult to find any reason to suppose 

 that T. saccharina is not native to its present habitat, and it is probable 

 that it occurs in the neighbouring mainland, which, however, up to the 

 present has not been visited. 



On the other hand its occurrence in Grenada and St. Vincent is more 

 probably due to accidental transmission in comparatively recent years. 



ADULT— DESCRIPTION AND VARIATION. 



Tomaspis saccliarina Distant 1909. (Plate I, P'igs. 1-4). 



General appearance : Length 7-9 mm. (^-^ inch), width across folded 

 wings 3"5-4".5 mm. (^-J inch). Forewings dark brown with two narrow 

 transverse bands of a lighter colour and sometimes parts of the base of 

 the wing also light. 



Head, pronotum and scutellum dark bronzy brown. Face and 

 prothorax and a sublateral band on each side of the abdomen beneath, 

 Blackish bruwn. Legs dark blackish brown except at base of front and 

 mid tibiae and base of femora of hind legs, which are lighter. Abdomen 

 above and beneath red-brown in the male and brown in the female. 

 Vertex broader than long, rounded in front, centrally carinate and 

 longitudinally depressed on each side before the eyes. Face compressed 

 centrally, longitudinally carinate, somewhat regularly rounded to 

 clypeus. E^'es black. Tegmina less than three times longer than broad. 



*I cannot quite agree with the word "prefers" \n No. (2). 



