October, '16] SMITH: defining host relationships 479 



predaceous insect is one which requires more than a single individual 

 of the host species for completing its development and this require- 

 ment would seem to necessitate a more or less well developed means of 

 locomotion. There is, however, no definite division between parasi- 

 tism and predatism and in certain cases it is difficult to know whether 

 to call an insect a parasite or a predator. A case of this kind is the 

 Pteromalid scale-parasite Scutellista cyanea. If we follow the defini- 

 tion given above Scutellista might come in either the parasitic or 

 predaceous category. The female Scutellista deposits her eggs be- 

 neath the adult black scale. The parasite larva, however, feeds 

 upon the eggs of the host and requires a large number, frequently 

 several hundred, to complete its development, although it always 

 matures beneath and upon the eggs of a single host scale. The ques- 

 tion then arises as to whether we should call Scutellista a parasite of 

 the black scale or a predator upon black scale eggs. The definition 

 of the term parasite might he enlarged to fit cases of this kind by say- 

 ing that a parasite is an entomophagous insect which requires but a 

 single individual host insect, or the eggs of a single individual, to 

 complete its development. But in calling to mind the life-histories 

 of various kinds of parasites we find that even this enlargement of the 

 definition as generalh^ understood will not serve to define the host- 

 relations in all cases. Macrorileyia oecanthi Ashm., a Chalcidoid 

 parasite (?) of the tree-crickets, carries us a step farther. This so- 

 called parasite lives in the pith of the twigs in which the tree-crickets 

 have deposited their eggs and upon which it feeds. Unlike Scutellista, 

 however, it maj', and frequently does, feed upon the eggs of more than 

 one individual tree-cricket, and by reason of this approaches still more 

 closely to predatism. There are many examples of this type of host- 

 relations. In Italy there occur two Chalcidoid enemies of the alfalfa 

 weevil, one a Pteromalid and the other an Eupelmine, of similar habits. 

 The eggs of the alfalfa weevil and other species of Phytonomus are 

 deposited within the stems of the host-plant in clusters. The two 

 parasites mentioned here feed upon these eggs not as egg-parasites 

 but as predators, often devouring egg-masses from several different 

 weevils. Excepting for the fact that one is protected and the other 

 feeds in the open, there is no essential difference between these so-called 

 parasites and the larva of Leucopis, for example, which feeds upon the 

 eggs of mealy-bugs, or the larva of the Brown Lacewing, Hemerobius, 

 which feeds upon the eggs of the same host. Scymnus, Hyperaspis 

 and many other ladybirds have similar habits. In view of these facts, 

 therefore, we can scarcely say that there is a definite line of demarca- 

 tion between parasitism and predatism, but the two, like geographic 

 races, intergrade, the two extremes being quite distinct. In fact there 



