298 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 



Fig. 31. — Maceobasts unicolor.— a, normal, gray, form ; b, 

 black (rmirina) form; c, d, male and female antennae of either. 

 (After Riley.) 



therefore, to a parasitic life, I began to conclude, from the facts just stated, that the 

 parasitism was of another kind, having satisfied myself by various experiments that 

 thetriungulins did not feed on roots. Few discoveries are stumbled upon. We find as a 

 rule that only which we anticipate or look for. Late last fall, in digging up the eggs 

 of the Rocky Mountain locust (Calo^Henus spretus) at Manhattan, Kans., the pseudo- 

 pupaj were not unfrequently met with. The thought at once occurred to me that 

 locust-eggs might be the proper food for these blister-beetle larvse, and it was encour- 

 aged by the fact that the Meloids abound most in those dry Western regions where the 

 Acrididae most prevail, and by a pretty distinct recollection, which my notes support, 

 that the years when the vesicants were most injurious to potatoes had been preceded 

 by dry falls, during which there had been much locust injury and, necessarily, unusual 

 locust increase. The suspicion thus raised that these blister-beetles preyed in the 

 preparatory states upon locust eggs was confirmed last spring by finding the larvae 

 of difi'erent ages within the egg-pods and devouring the eggs of Caloptenus spretus. Mr. 



A. N. Godfrey had, also, no dififi-, 

 culty, under my directions, in 

 findiug them last May at Manhat- 

 tan ; while they were sent to me 

 amoDg other locust-egg parasites 

 by Mr. Seth H. Kenney of Mor- 

 ristowu, Minn., and from Saint 

 Peter's, in the same State,by Prof. 

 Cyrus Thomas. 



From such larvae preyiog upon 

 the eggs of spretus I have reared 

 the unicolorous form of Epicauia 

 cinerea (Forster), or the Margined 

 blister-beetle ;6o the Epicauta pennsylvanica (DeGeer),6i or the Black blister-beetle ; the 

 MacroMsis iinicolor (Kirby),^^ or the Ash-gray blister-beetle ; and the form of it de- 

 scribed as murina by LeConte, or the Black-rat blister-beetle. 



Since then I have found it very easy to trace the larval habits and development of 

 the two more common potato-feeding species around Saint Louis, viz, the Striped blis- 

 ter-beetle (^j^icatttovi/tafa Fabr.)^^ and the Margined blister-beetle {marginata Fabr.) 

 just alluded to. 



Careful examination of locust-eggs in the vicinity of potato-fields frequented by these 

 beetles shows a varying proportion of the egg-pods affected, and in some locations nearly 

 every pod of the Differential Locust {Caloptenus differentialis) will contain the Epicauta 



larva. The eggs of this locust 

 are laid in large masses of 70 

 to about 100. The pod is but 

 slightly bent, rather compact 

 outside, while the eggs are ir- 

 regularly arranged, and capped 

 with but a shallow covering of 

 Fig. 3-2.— Caloptenus diffeuextialis. (After Eiley.) mucous matter. It is the egg- 



pod of this species which the larvaj of the two blister-beetles in question prefer; for 



69 The black, gray-marfiined form, very appropriately described by Fabricius as warginata, is referred 

 to cinerea Fors er'by modern systematists, and specitically united with it by Dr. Horn. Yet the fact 

 remains that the two are not ordinarily, if ever, found commingled. The margined form is very com- 

 mon in potato-fields in Missouri. It shows little variation and is found almost invariably in conjunction 

 with vittata, but not with tli3 unicolorous form in question, which is most common farther west and 

 occurs abundantly without the margined form— all which is against the specific union of the two. 

 - 61 — atrata Fabr. 



^-= cinerea Y ahr., Fabr ieii 'Lac, murina l,eG., debilis Loc. I accept Dr. Horn's conclusion that the 

 las*; two are but poorly developed forms of this species. Yet the murina form is not due to rubbing 

 or injury, but issues from the pupa without a trace of gray scales on the elytra. 



63 == lemniscata Fabr. Dr. Horn retains lemniscata as a distinct spe ies in his Eevision already re- 

 ferred to. The outer stripe in the bi-vittate specimens divides up in others po as to give the tri-vittato 

 character on which lemniscata is founded. Both extremes and every possible variation between them 

 occur constantly together in the same potato-field in Missouri, and there are no other differences of spe- 

 cific value. 



