346 



DISTRIBUTION OF HOWARDULA 



are the dimensions and other details of these young but already spermatized 

 individuals, as found both in the soil and in very young beetle-larvae, which 

 in the body-cavity of the host reach the above seven to ten times longer, mature 



3.4 (?)12. 28. -91. (?-)94.8 

 form: 7 ::::: 7 7 ^ ^~7 0.54 



3.7 



2.8 



Fig. 2. Map showing distribution of the nema 

 Howardula benigna as disclosed by examinations in 

 1921 The aim was to examine at least 100 cucumber- 

 beetles from each locality. This aim was achieved 

 in most cases. 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, but the 

 figures for different regions varied much. Where the 

 percentage of infestation was highest, the nematism 

 was highest. The presence of the nema does not 

 exclude other internal parasites, such as other insects 

 and gregarines. Only one other nemic parasite was 

 observed, represented by a single Nova Scotian speci- 

 men. About 1500 D. tittata were examined. Below 

 are the addresses of those who kindly contribut J 

 insects for examination. 



Balduf, W. V. Marietta, O. 

 Campbell, R. Alhambra, Cal. 



Hall, Dr. M. C. Chevy Chase, Md. Ross, W. A. Vineland Sta., Ont. 

 Harned, R. W. Agr. College, Miss. Smith, C. E. Baton Rouge, La. 



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



Walters, M. J. New London, Ct. 



Cobb, Dr. F. Ann Arbor, Mich. High, M. M. Kingsville, Texas. 

 Cobb, V. Whitman, Mass. Kelsall, A. Annapolis Royal, N. S. 



Centner, L. Lansing, Mich. 



, . 

 Raps, E. M. Oakton, Va. 



Watson, J. R. Birmingham, Al. 



Habitat: Common in the body-cavity (abdomen, thorax and even head) of 

 all stages of Diabrotica vittata, trivittata, and 12-punctata, especially the two for- 

 mer, infesting the two sexes about equally. 



My attention was called to this nema by Mr. W. V. Balduf, Assistant Ento- 

 mologist, Ohio Agricultural Experiment Station, Marietta, Ohio, where he dis- 

 covered the larvae in the course of experiments on Diabrotica. Owing to the 

 economic aspect of the subject, beetles sent me by Mr. Balduf were exhibited, 

 dissected, at the Washington Helminthological Society's meeting, March 17, 

 1921. Examination revealed the adult female form, which is so flaccid and 

 otherwise deceptive as to cause it rather easily to be confused with the internal 

 organs of the host by one not already versed in both insect and nemic anatomy. 

 With the aid of Dr. F. H. Chittenden and colleagues, Federal Bureau of 

 Entomology, and others, the geographical distribution of the nema was 

 studied with results shown on the accompanying map, which indicates that the 

 distribution in the spring and summer of 1921 was probably nearly coextensive 

 with that of the main hosts, Diabrotica vittata Fab. and trivittata Mann. The 

 nematism is often high and affects on the average about 20% (0%-70%) of the 

 insects. Beetles from a locality where they are not nematized are larger, brighter, 

 more vigorous. Thus twenty-five beetles from an uninfested lot were much 



