HOST-SELECTION 319 



Phasiine group mainly attack Pentatomidse, but, as Thompson 

 and Parker (1927) point out, the genera, Frercea, Weberia and 

 Rondania are parasites of Coleoptera. Of four related Dexiine 

 genera, Thelaira, Fortisia, Cyrillia, and Thrixion, their hosts are 

 Lepidopterous larvae, the Chilopod Lithobius, the Isopod 

 Metaponorthus and certain Phasmidae respectively. The relations 

 of Tachinids parasitic upon woodlice (Oniscidae) have formed the 

 subject of a detailed study by Thompson (1934). The available 

 data appear to suggest that the parasitisation of woodlice depends, 

 in the main, on the habits of the latter. Those Oniscidge living in 

 large colonies, under loose bark of logs, are the kinds most usually 

 parasitised, for the reason that they frequent situations favourable 

 to attack. 



Among the many parasites of polyphagous habits it will suffice 

 if two examples be quoted. The Tachinid Compsilura concinnata, 

 which was introduced from Europe into the United States in 

 1906, has been reared, according to Webber and Schaffner (1926), 

 from over ninety species of American insects representing three 

 orders — Lepidoptera are mostly selected, and no less than eighteen 

 families are included in their host list. There appears to be no 

 one distinctive character common to all its hosts — neither colour 

 nor colour-pattern ; hairiness or absence of hairs ; low-feeders, 

 bush-feeders or tree-feeders ; habit, whether the hosts be 

 gregarious or solitary, diurnal or nocturnal ; specific food-plants, 

 whether they be Gymnosperms, Monocotyledons, Dicotyledons or 

 lichens ; odour or absence of odour ; presence or absence of 

 urticating hairs, etc. — as Thompson points out, all these categories 

 are represented among the host-species, and from whatever 

 standpoint this varied assemblage be considered its members have 

 in common only the fact that they are all hosts of Compsilura. 

 Among Hymenopterous parasites a parallel example is afforded 

 by the Ichneumon Hemiteles areator, which has been reared from a 

 remarkable range of hosts comprising many Lepidoptera, various 

 Hymenoptera, including other Ichneumonidse, besides several 

 Coleoptera and Diptera. 



In the two foregoing examples the insects mentioned are 

 endoparasites, and it appears probable that at least some of the 



