42 Gnayule. 



ANIMAL PARASITES. 



The root-system, particularly the tap-root and its larger branches, 

 are frequently found to be infested with two species of the Coccidae, 1 Cero- 

 puto yucca (Coq.), and a species of Orthezia, distinguishable from the for- 

 mer by the fluted, waxy egg-case attached to the abdomen. The number 

 of these insects found on plants in the field is not inconsiderable, and may 

 be responsible for lesions in the root-tissues which affect the growth of 

 the plant. But of more importance is the circumstance that they occur 

 in greater numbers upon seedlings raised under cultural conditions in 

 wooden trays. Plantlets a few centimeters in height have been found 

 with a dozen or more large individuals on the tap-root, the diameter of 

 which was not as great as the breadth of the mature insects. They may 

 therefore easily be responsible for retardation of growth, though external 

 evidence of lesions has not been noted. 



Field plants especially are often infested below the surface of the 

 soil by a scale, identified by Dr. C. L. Marlatt as Targionia dearnessi Ckll. 

 This is a widely distributed species in this country. Large tap-roots are 

 frequently half covered by this parasite. 



A gall insect attacks the leaves and inflorescence. The female punc- 

 tures the young leaves and stems, the peduncles, and even the bracts of 

 the capitula, and the resulting galls produce marked distortion. Many of 

 the affected leaves fail of anything approaching normal development ; the 

 peduncles are hypertrophied unevenly and become very much contorted, 

 and the inflorescence fails to develop. The net result of the work of this 

 insect is to reduce the rate of growth very materially and to cause a prac- 

 tically complete abortion of the flowers and, therefore, of the seed. The 

 plants affected are readily recognized on account of the irregularity and 

 lumpiness of the terminal growths. The stems proper do not seem to be 

 affected, as the insect appears to commence its work toward the close 

 of the season of growth and to confine itself to the last-formed leaves, 

 which remain attached throughout the winter, and to the inclosed young 

 inflorescences. The increase of growth in the stem is, however, affected 

 indirectly, and the annual accretions frequently amount to less than i 

 cm., and scarcely ever to more than 2 cm., during the period of attack. 

 Many plants in circumscribed areas are subject to the attacks of these 

 insects, and it may readily become a serious menace to both the growth 

 of the plants and to their seeding power. The following notes have been 

 kindly furnished me by Dr. Mel. T. Cook: 



The study of this material presented many difficulties, as must necessarily be 

 the case when it is not possible to make a field study. 



A gall produced by Cecidomyia parthenicola on Parthenium 2 in New Mexico has 

 been described by T. D. A. Cockerell in Entomologist, July, 1900, p. 201. The gall 

 before me does not fully correspond with Cockerell's species, and yet I should hesi- 

 tate to say that it is an entirely different species without further study, which is im- 

 possible with the material in hand. Dissection of the material showed two entirely 

 different species of larva and immature insects, cecidomyid and cynipidous, while a 

 study of the histology presented certain confusing and anomalous characters. 



1 Kindly determined for me by Mr. J. G. Sanders, through the courtesy of 

 Dr. L. O. Howard. 



2 Parthenium incanum, presumably. 





