776 



SCIENCE 



[N. S. Vol. XXVI. No. 675 



and indicates the value of further experi- 

 mental work in this direction. 



Another interesting and significant 

 large scale experiment of this kind was 

 carried on in the present year, also by 

 Professor Webster, which, while void of 

 practical results, is most significant and 

 valuable as indicating limitations. A seri- 

 ous enemy of grains and grasses, an 

 aphidid, known as the Toxoptera gram- 

 inum, made its appearance in the winter 

 -time in Texas, and gradually appeared 

 farther and . farther north until in July 

 it was found across the Canadian border. 

 At certain periods this Toxoptera is always 

 practically exterminated by a parasite of 

 the genus Lysiphlebiis. At the time when 

 the Lysiphlebus in Texas is abundant, and 

 is gaining control of the situation, the 

 Toxoptera is doing its worst damage, and 

 is comparatively unparasitized in more 

 northern regions, such as Oklahoma and 

 Kansas. It was considered that if the 

 parasites could be collected in Texas in 

 very large numbers, and transported to 

 Oklahoma or Kansas, the introduction of 

 these large numbers of parasites would 

 hasten the destruction of the Toxoptera, 

 remembering all the while that native-born 

 Lysiphlebus in small numbers were already 

 beginning to develop in the Oklahoma and 

 Kansas fields. A number of experiments 

 of this kind, and on a very large scale, 

 were carried on; some work was done by 

 Mr. S. J. Hunter, of Kansas, and much 

 was published about the result of this work 

 in the month of May; but the careful, 

 large se^le and check experiment carried 

 on under Professor' Webster in the same 

 month seems conclusive proof of the fail- 

 ure of such work. 



One experiment in particular may be 

 described : On May 13 two fields of winter 

 oats near Manhattan, Kans., each contain- 

 ing four acres, were selected for the experi- 

 ment. These fields were sufficiently widely 



separated, and one of them was used as a 

 check. Into the other was introduced some 

 millions of parasites sent from Wellington, 

 a point much farther south. Careful count 

 showed that in the experimental fields the 

 percentage of native parasitism at the be- 

 ginning of the experiment was from 3 to 7. 

 On May 18 the parasites from Wellington 

 were introduced and liberated ; on May 23 

 the parasitism in this field had increased 

 only about 2 per cent., whereas in the check 

 field, in which no parasites had been liber- 

 ated, it had increased 12 per cent. On 

 May 27 the percentage of parasitism in the 

 field into which parasites had been intro- 

 duced had reached 27 per cent., while in 

 the check field it was 32 per cent. It was 

 thus cleai"ly demonstrated that even under 

 weather conditions favorable for the devel- 

 opment of parasites, an introduction to the 

 extent of millions carried out under field 

 conditions does not indicate enough effi- 

 ciency to afford any encouragement for the 

 use of this measure in the protection of the 

 grain fields in case of future attacks. 



One of the most important features which 

 have come to the front of late, although 

 often suggested in earlier writings, is the 

 value of a variation in farm practise in its 

 effect upon insect control: the rotation of 

 crops has always been known to be of prime 

 value, but further than this; even in the 

 ease of constant recropping upon the same 

 land of the same growth, it is often found 

 that slight variations in time of seeding, in 

 time of harvesting and in method of culti- 

 vation will produce important effects upon 

 insects and vegetation. Many of the state 

 entomologists have taken up this line of 

 thought, and have worked out practical 

 results with farm insects, and also with 

 insects that affect truck crops. The ad- 

 vances in this direction and in others are, 

 in fact, so numerous that even a cursory 

 summary would be difficult. 



In the 1894 address the rise and the then 



