190 



SCIENCE 



[N. S. Vol. XXXI. No. 788 



Egbert Bruce Brinsmade, B.S. (Washing- 

 ton University), E.M. (Lehigh), has accepted 

 the chair of mining engineering at West Vir- 

 ginia University, replacing Henry Man Payne, 

 who has gone into other lines of work. 



Mr. O. T. Jones, of the Geological Survey 

 of England and Wales, has been appointed 

 lecturer in geology and physical geography 

 in University College, Aberystwyth. 



Mr. H. J. Seymour, B.A., of the Geological 

 Survey of Ireland, has been appointed pro- 

 fessor of geology in University College, 

 Dublin. 



DISCUSSION AND CORRESPONDENCE 



■^ THE GREEN BUG AND ITS NATURAL ENEMIES 



Professor Woodworth has very kindly sent 

 me in advance a copy of his review of " The 

 Green Bug and Its Natural Enemies." The 

 views advanced by him are interesting and his 

 interpretations somewhat out of the usual 

 order. 



1. He does not understand why data 

 from the experimental laboratory studies 

 were not used to show the potentiality 

 of the parasite, Lysiphlebus triiici, over the 

 green bug, Toxoptera graminum. No at- 

 tempt was made to use the data in that way, 

 since the contest between the two forms took 

 place, not in the experimental laboratory, but 

 under natural conditions in the open, over 

 territory from central Texas northward 

 through Oklahoma to central Kansas. Ac- 

 cordingly, it was stated (page 135), " The 

 average number of green bugs killed by a 

 single parasite under natural conditions is 

 probably much larger than the above figures 

 show," and reasons were there given for this 

 opinion. Since that time corroborative evi- 

 dence on this point has appeared as follows: 

 " The female LysipMehus is even more prolific 

 than the female Toxoptera. Mr. Phillips has 

 found females which had upwards of four 

 hundred eggs in their ovaries and Mr. Kelly 

 has reared in some cases 206 individuals from 

 a single mother Lysiphlebus.^ 



Obviously, then, figures or tables, such as 

 prepared by the reviewer, based on data ob- 

 » Circular No. 93 rev., p. 15, U. S. Dept. of 

 Agric, B. of Ent., June 23, 1909. 



tained under artificial conditions, would not 

 form a safe basis for conclusions upon the 

 outcome of such a struggle in the natural en- 

 vironments of the contestants. 



However, since the reviewer has placed 

 special stress upon the value of his tables it 

 should be noted, as showing their bearing upon 

 the laboratory experiments, that he takes the 

 minimum period, five days, for development 

 of the green bug and considers that as the 

 average. . That is, among 140 green bugs 

 reared in laboratory under daily observation, 

 four, or 2.8 per cent., gave birth to young on 

 the fifth day, and this percentage he rates as 

 the average. As a result he obtains 95,571 

 progeny for one green bug in thirty days, 

 whereas the author, using the average summer 

 rate, seven days, of development for 80 green 

 bugs reared in laboratory under daily obser- 

 vation, obtains for the same period 15,794 

 (page 95) — a difference of 79,777 on the first 

 basis of comparison. As to the parasite, the 

 reviewer takes the average rate (page 7 based 

 on results of several observers) of development 

 of parasite in the open field, seven days, for 

 his computation on the parasite. 



That is, the behavior of 2.8 per cent, of the 

 green bugs observed in the laboratory and the 

 behavior of the average of all parasites ob- 

 served in the open, are the factors which he 

 uses to compute the potentiality of the para- 

 site. Obviously, basal factors so unlike in 

 quantity and conditions furnish no reliable 

 foundation for comparisons from which to 

 deduct safe conclusions. Furthermore, these 

 factors are not representative of the data 

 from which they are supposed to be taken. 



Consequently, the subsequent computations 

 and deductions upon his table as brought out 

 by the reviewer, unique in themselves, would 

 not seem to require further consideration here. 

 The statement of the author regarding the 

 outcome of the struggle between the parasite 

 and its host was not based upon deductions 

 from the experimental laboratory data, but 

 from the records of continuous field observa- 

 tions made during the entire time of the 

 struggle by eight different reliable observers. 

 The seven from the university were stationed 

 from central Oklahoma to northern Kansas, as 



