INTRODUCTION Ixxxi 



A good many of the species of Nesoprosopis exhibit considerable variability and 

 this not merely affects superficial characters, such as the facial or other markings, but 

 important structures are involved. Thus in Nesoprosopis flavifrons I have noticed 

 variation in the amount of dilatation of the scape of the antennae, so that, in this 

 respect, some examples more nearly resembled the allied A'', anthracina than did 

 others. -^ Similar variation has been noticed in other species having a strongly dilated 

 scape. The small median facial plate above the clypeus sometimes varies in its relative 

 length and breadth. In the case of N. difficilis and N. volcanica, two very similar 

 species, often occurring together, I found that the majority of many specimens that 

 I examined could be distinguished by the shorter supraclypeal plate of the former, 

 but that examples occurred in which this distinction was not maintained. These two 

 species, I should add, are perfectly distinct by other constant characters. 



Some of the parasitic species are especially variable in size, and this variation 

 is often striking, when examples from different localities are compared in series. 

 It is due entirely to the amount of food supply consumed, and this amount depends 

 on the species of the host, in the nest of which the parasite is nurtured. On one 

 occasion I obtained specimens of N. volatilis of gigantic size for this species, these 

 having been bred in a colony of N. assiinit/ans var. oa/mensis. The same species 

 when obtained from colonies of N. /acta or N. difficilis is much smaller. In some 

 localities one may find very large and very small examples of N. hilaris in the same 

 station, the former being bred on the store of N. assimulans and longiceps, the latter 

 on that of N. blackbtirni. As will be seen from these remarks, the parasitic Nesoprosopis 

 are not at all confined to one species of host. However, they only infest the nests 

 of such species as burrow in the ground. Those that burrow in the trees have never 

 been found to be affected. 



These latter, however, have their true parasites (i.e. not inquilines, as the others 

 would be more correctly called) in the shape of the Encyrtid Chalcidoids of the genus 

 Etipclmus, which are bred from the cocoons of some of the larger species, and very 

 probably affect the smaller also. On one occasion I saw an extraordinary congregation 

 of males of one of these Etipclnms, forming a complete circle around the entrance of 

 the burrow of Nesoprosopis setosifrons, the heads of all the parasites resting on the 

 edge of the mouth of this burrow. Their antennae were kept in constant vibration 

 and those of each individual were continually crossed with its neighbour's, evidencing 

 great excitement. No doubt the burrow, which was one of several in a very hard 

 dead tree, would, if opened, have revealed one or more females of the Eupelinus ready 

 to emerge. A^. fuscipennis, a species common in the mountains near Honolulu, is 

 attacked by the same or an allied parasite, as also is its var. obsctiripes on Maui. 



Many of the species of Nesoprosopis are extraordinarily abundant and I doubt 

 whether any species is really rare. Some of them appear at irregular intervals and 

 so in any locality are easily missed. My experience with the remarkable litde 



F. H. I. !■ 



