December 30, 1921] 



SCIENCE 



669 



beetles from an uninfested lot were much 

 larger and averaged seventy per cent, heavier 

 than a similarly chosen twenty-five from a 

 fifty per cent, nematized lot. Anatomical evi- 

 dence shows the infested female beetles to be 

 less fertile than the non-infested, doubt as to 



Fig. 3. The map-figures give the percentage of 

 beetles found infested by Howardula. The figures 

 for different localities a few miles apart in any 

 given region usually were in substantial agreement. 

 Where the percentage of infestation -was highest, 

 the nematism was highest, and vice versa. The 

 presence of the nema does not exclude other inter- 

 nal parasites, such as other insects and gregarines. 

 About 1,500 D. vittata were examined. Below are 

 addresses of those who kindly contributed insects 

 for examination. 



Balduf, W. v., Marietta, O. 

 Cobb, Dr. F., Ann Arbor, Mich. 

 Cobb, v.. Whitman, Mass. 

 Chapin, E. A., Falls Church, Va. 

 Fenton, E. A., Ames, Iowa. 

 Flint, W. P., Urbana, lU. 

 Gentner, L., Lansing Mich. 

 Hall, Dr. M. C, Chevy Chase Md. 

 Harned, E. W., Agr. College, Miss. 

 Haseman, L., Columbia, Mo. 

 High, M. M., Kings ville, Tex. 

 Kelsall, A., Annapolis Royal, N. S. 

 Eaps, E. M., Oakton, Va. 

 Riley, Wm. A., St. Paul, Minn. 

 Ross, W. A., Vineland Sta., Ont. 

 Smith, C. E., Baton Rouge, La. 

 Thomas, W. A., Chadbourn, N. C. 

 Walters, M. J., New London, Ct. 

 Watson, J. R., Birmingham, Ala. 



diminished fecundity vanishing where the 

 female host harbors a dozen or more adult 

 nemas. In such cases the mere relative volume 

 of the parasites is convincing evidence of 

 handicap. See Fig. 1. Mr. Balduf in a let- 

 ter speaks of beetles, many of which "died 

 of nemas." I have no rigid proof of such 

 deaths, but believe them very probable and at 

 times numerous. 



In none of the numerous lots of beetles 

 examined was the rate of infestation by any 

 other zoo-parasite as high as by Howardula, 

 with the single exception of a forty-three per 

 cent, dipterous infestation; but no note was 

 made of degrees of phyto-infestation (cucum- 

 ber-wilt organism, etc.). 



As many as thirteen thousand nema larvse, 

 by count, have been removed from the body- 

 cavity of a single Diabrotica vittata, and no 

 doubt the number may go much higher. On 

 several occasions twenty or more adult How- 



Fig. 4. Head of very young cucumber-beetle 

 larva and of young Howardula at the time of 

 its entrance. The mandibles of the grub, mnd, 

 would seem to be impassable to the nema. 



ardulas have been taken from a single beetle. 

 Theoretically these should produce some forty 

 thousand larvae or more. The older female 



