40 HOMOPTERA 



history of these parasites which does not lend itself readily to the usual methods of rearing. However, 

 Kornhauser (1916, 1919) successfullj' reared parasites of Thelia bimaculala. 



Wildermuth (191 5) reports a small red mite (Eryihraus sp.) feeding on membracid eggs and the 

 writer has found similar mites, probably of the same genus, as external parasites on a number 

 of species. 



It is likely that Ihe hard, sharp pronotum of the adult membracid, the protective coloration, 

 and habits of the nymphs, and the protection given to both nymphs and adults by attendant ants, 

 particularly the so-called « fire ants » of the tropics, which the writer can testify are among the worst 

 of the enemies of the coUector, are sufficient factors to discourage all but the most courageous of the 

 usual insect enemies of insects and explain the comparative immunity of membracids to these foes. 



MIGRATIONS 



The migrations of the Membracida are apparently very slow both as regards change of locahty and 

 change of host plants. In any given region the same forms may be found in the same locality year 

 after 3'ear, while a neighboring locality, offering the same natural conditions, remains unentered. The 

 writer has often had the experience of collecting in a strange region, under the guidance of a local 

 entomologist who had taken membracids in a certain particular place « several years ago » ; almost 

 without fail the insects were there as usual. 



The same is true in regard to migrations from one plant to another. It often happens that one 

 tree may be literally covered with individuals of a species, while another tree of exactly the same kind, 

 in close proximity to the first, may be unmolested; and these conditions may be noted season after season. 



The reasons for such reluctance in seeking new localities and new hosts are not evident. The 

 insects fly weil for short distances and should be able without difficulty to spread over a considerable 

 area in a season provided the desired host is abundant throughout the area. This, however, appears 

 not to be the case and is probably one of the reasons why the Membracida are not often noted as 

 economic pests. 



The migration of the nymph from the hosts on which the eggs are laid to the feeding plant, 

 in cases in vvhich such movement is part of the life history, is regular and definite, but the distance 

 covered is never great. 



The adults avoid flights of any distance, and if disturbed they generally leave the twig with a 

 quick leap, fly rapidly in a narrow circle, and return to the plant from which they were driven. Even 

 in a series of trees close together, all of the same kind and all inhabited by membracids of the same 

 species, it is unusual to see the insect fly from one tree to another. The greatest movement noted in 

 the field is found in areas covered by low grasses or other carpeting vegetation in which the insects fly 

 erratically about when disturbed. 



We believe that this disinclination for migration explains why the various species of Membracida 

 seem to be so limited in distribution, why there are no cosmopolitan species, and why there are so 

 many species. It is interesting to note that in regions broken by many barriers, such as the islands 

 of the East Indies, each island has in general its own distinct species while the genera are common to 

 the region. We believe that this indicates tliat the islands are the fragments of a large ancient land- 

 mass which has been submerged long enough to prevent the isolated insects from interbreeding and to 

 develop specific characters but not long enough to destroj- the more general and fundamental generic 



