E NT O M 0 1 ' II T II ( ) It E A E OF THE UNITED STATES. 



136 



fected. Of the different stages of insects the imagines, larvae and pupae may all he 

 parasitized, and in some instances a single parasite may attack all t hese stages in one Mi- 

 more species of the same or different orders; while in others it may confine itself to a 

 single stage or species. 



Entomogenous plants may in a general way be referred to five principal groups: one 

 including the bacterial forms which produce disease in insects; a second represented by 

 certain entophytous algae; and three others all belonging to the fungi proper. 



The first mentioned group, represented by the Bacteria, is chiefly of interest from an 

 economic, rather than from a botanical point of view, as the supposed cause of destruc- 

 tive epidemics among useful as well as noxious insects. Instances of this kind are pre- 

 sented by the disease known asjiacherie so destructive to silk worms, and in affections 

 of a similar nature in other insects, where the "active principle " has, in some cases, 

 been traced to bacterial forms which have been considered sufficiently peculiar to receive; 

 distinctive names. The systematic study of the group is necessarily one of great diffi- 

 culty, and any opinion as to the validity of specific distinctions in such cases can only 

 be formed by specialists in this department; but from a practical standpoint the existence 

 of such affections promises to afford an important means of defence against noxious in- 

 sects. 



The second group includes a small number of peculiar filamentous algae, represented by 

 Enter dbry us and its allies, that live attached to the digestive tracts of certain myriapods 

 and coleopterous larvae. They are apparently nearly related to Oscillaria or Beggiatoa 

 among the Protophytes; but, owing to insufficient observations upon them, their exact af- 

 finities are unknown. Their habit is probably one of commensalism, rather than of true 

 parasitism; the partially digested food of the host being absorbed directly from the di- 

 gestive tract. 1 



The fungoid parasites of insects are, as before mentioned, represented by three chief 

 groups : the Entomophthoreae, the Laboulbeniaceae and the entomogenous forms which 

 constitute the bulk of the genus Cordyceps. Since the first of these is to receive spe- 

 cial consideration hereafter, it need only be said that its members are closely allied to the 

 Mucorini among the Zygomycetes, and are entomogenous with few exceptions. 



The Laboulbeniaceae constitute a small group of very peculiar and minute forms which 

 have been placed by DeBary among the doubtful Ascomycetes. Their parasitism is 

 an external one, which apparently results in little if any inconvenience to the host; each 

 individual being fixed by a pedicellate attachment to the legs, thorax or other portion of 

 the affected insect. Several genera on Diptera, Coleoptera, etc., are described by Pey- 

 ritsch 2 to whom we are principally indebted for our knowledge of the group, although the 

 first genus of the family (Laboulbenia) was described and figured by Robin. 3 The 

 single American representative thus far recorded has been described by Professor Peck 

 as Appendicularia eyitomophila, n.g. et sp. 4 



The pyrenomycetous genus Cordyceps affords by far the most conspicuous examples 

 of entomogenous plants, many of which are of large size, or brightly colored, and have 



1 See Leid.y, Smiths. Contr. to Knowledge, v, pp. 1-67 

 (1853) and Robin I. c, p. 395. 



2 Sitz. d. Akad. wiss. Wien., 64, i, p. 441 (1871) : 68, I, 



p. 227 (1873): 72, I, p. 377 (1875), plates. 



3 I.e., p. 622, plates. 



4 Peck, 38th Report, p. 95, with plate. 



