196 



on this species states that the males are excessively rare, only 

 one occurring to about a thousand females. The existence of 

 this habit of thelyotoky is obviously a great advantage to a 

 species invading a new region, since it might become estab- 

 lished under favorable conditions from a few females or even 

 from a single specimen. Conversely the arrhenotokous habit 

 of reproduction may act disadvantageously before a species is 

 well established, since the rapid dispersal which usually takes 

 place will tend to increase the difficulties of the sexes finding 

 each other, and thus restrict the necessary fertilization of the 

 females. 



In conclusion we may summarize our knowledge of the 

 local Encyrtid fauna somewhat as follows: The endemic 

 fauna is represented by five genera with about twenty to 

 twenty-five species. Eighteen genera of introduced Encyrtidae 

 have been recognized already, with two or three species as yet 

 unworked which may raise the number of genera to about 

 twenty. The source of three species is undoubtedly !N"orth 

 American, and the rest of the immigrant species presumably 

 have arrived mostly from the Australian, Polynesian or Orient- 

 al regions, although we have no very definite clews to the 

 origin of several. At least two and possibly four species hav- 

 ing been collected years ago but not recovered since are prob- 

 ably extinct in the Islands. Only two species are definitely 

 known to have been introduced intentionally, although several 

 others may have been as the records of early introductions are 

 fragmentary. About seven of the immigrant species are mo- 

 noxenotic and eleven others are polyxenotic, the former having 

 been introduced presumably concurrently with their hosts, the 

 latter not necessarily so. Peculiarities in the habits and life 

 history have had some influence on the introduction and estal;- 

 lishment of the Hawaiian Encyrtidae, since oviposition in the 

 earlier stages of the host, thelyotokous reproduction and the 

 polyxenotic habits of certain species are obviously advantageou-^ 

 in the dispersal of the species into new regions. 



