Thoughts on the Hymenoptera Trichogrammatidae etc. 79 



Species of Trichogramma appear to be scarce in Australia though 

 there is one species which must be widely distributed along the east 

 coast and numerous in individuals since I have frequently captured 

 it. Again it shews the great resemblances between the species of the 

 two countries. At first identified as the wide-spread minutum of Riley, 

 I was lead finally to consider it distinct, though the differences certainly 

 are minute; this must be expected with this family, however. There 

 are also Australian species of Tumidiclava, Abbeila, Aphelinoidea, 

 Brachistella, Uscana and Ufens all of which closely resemble their 

 North American congeners, some very closely. It may be that the latter 

 are geographical variants of those Australian forms wich they so closely 

 resemble, which had migrated and subsequentjy varied in their new 

 life; but it may be just as likely that they descended from some one 

 ancestor of the genus which had migrated, prospered and given rise 

 to diverse species. Thus, I do not think that these species of the 

 two continents which resemble each other more than they do any 

 other species of the genus, are necessarily directly related but have of 

 necessity a common ancestor. Heredity and its action, however, 

 must incline us to believe that the great likenesses of the widely separated 

 species means direct relationship, however difficult it may be to believe 

 it. This the more so, since the liknesses are structural and fundamental. 

 In the heat of the tropics, the long exposure to great dryness and to 

 great wetness and the brilliancy of the sun, it should be expected 

 that the species abounding ther ewould be more intensely colored than 

 with the species living in a more temperate climate where the light 

 is less intense and life more sluggish, But, the more uniform conditions 

 in the tropics seemingly counteract to some extent the tendency 

 which the factors named would have upon coloration and as a whole 

 there is not a great contrast between North American and Australian 

 species of the family. 



The difficulites in explaining how, many centuries ago, these 

 minute insects scattered themselves over the earth are great, still 

 the available explanations are not highly improbable and might well 

 have occurred. There can be no doubt that in recent years some of 

 the species like Oligosita americana, Abbella subflava, Trichogramma 

 minutum and Trichogrammatoidea nana have beencarried from one coun- 

 try to another by commerce with their hosts which in turn were trans- 

 ported within their host plant. In the case or the first two species, 

 there is very little doubt but that they were introduced into Australia 

 for instance with their hosts in cultivated wheat and it is highly pro- 

 bable that the last was likewise introduced with its host in connection 

 with sugar-cane. None of these species appear to be common in 

 Australia and they were taken in localities which makes the above 

 the more likely. Distributions of a Hke'kind have been intentionally 

 made by entomologists and this proves that its occurrence is easily 

 possible at the hands of unconscious men. 



But thousands of years ago commerce was very much restricted 

 and infinitely lower. At one time it must have been absent. Whole 



1. Heft 



