Colour-groups of the JTaivaiian Wasps, etc. 701 



applies to species which are known as being plastic 

 outside the islands, i. e. ones which have formed 

 marked varieties or races in countries different 

 from the one whence they were imported to 

 our islands, but which they, no doubt, reached 

 naturally, and at a much more remote period. 



From my knowledge of insects generally I should say 

 that species we call very variable are usually really con- 

 stant in their varieties, i. e. the varieties themselves are of 

 regular occurrence in nature — some rarer some commoner, 

 like species. It evidently requires much time to alter 

 either species or varieties. What a time it must have 

 taken to produce the eighteen genera of Drepanididae, a 

 family peculiar to the islands ! This and the extreme 

 specialisation of so many of the genera seem to point to 

 an ancient excessive competition, unrealisable on present 

 conditions. 



I suspect that some day a widespread cause inducing 

 plasticity will be discovered. It must be remembered 

 that many of our commonest imported insects have no 

 enemies at all to keep them constant by selection, but they 

 have not begun to vary yet* 



* [The following contribution to this discussion was contained in 

 a letter written by Dr. Perkins from Honolulu, May 20, 1912 : — ] 



I am astonished after ray experience here at the permanency of 

 specific characters. When I see the enormous changes in climate 

 and general conditions produced by the white man's destructive 

 work, and compare examples of all sorts of insects collected to-day 

 with those taken over 75 years ago by old collectors, or 30-40 years 

 ago by Blackburn, I should have expected to have found at least 

 some perceptible difference between the individuals after so many 

 generations (things breed all the year here, many of them average a 

 brood to a month or six weeks). 



Again, the conspicuous dominant wasps of the genus Polistes 

 introduced nearly half a century ago — more conspicuous and fierce, 

 and more numerous than any Odyneri— might have been expected 

 to influence the more plastic of the indigenous species, viz. those 

 which have a coloration that could be easily changed to resemble 

 the new arrivals. In general it appears that an enormous time 

 must be allowed for specific change, unless it occurs abruptly and 

 suddenly. We have lately had a tropical American Odynerus 

 introduced here, of quite a different type from our groups ; but its 

 appearance could easily be arrived at by some of the native species. 

 This new species (no doubt, imported by man) is already, after a 

 year or so, a most dominant species. Theoretically it should be 

 badly off, as it would be vmknown to our endemic birds, etc., and it 

 is not very startling in colour. 



