122 ENTOMOLOGICAL NEWS. [March, '08 



Winged Aphids. 



C. W. WOOD WORTH, Southern California Pathological 

 Laboratory, Whittier, Jan. i/th, 1908. 



In the course of a study of the cabbage aphis, Aphis bras- 

 sicae, it was noticed that the wilting of the plant resulted in 

 an immediate slowing down of the birth rate. This season has 

 thus far been unusually dry in the southern part of the State, 

 and in almost all fields there have been innumerable cases of 

 evident diminution in the number of aphids without much 

 parasitism or sign of fungus or bacterial diseases. A leaf 

 badly curled and almost entirely covered on one side by the 

 aphids first shows a spontaneous production of young with 

 wing pads. When these young have become full grown they 

 fly away and the leaf becomes ultimately entirely free from the 

 insects, except perhaps the bodies of a few swollen up parasi- 

 tized individuals that may still remain and the cast skins that 

 sometimes cling to the surface. 



There may be some connection between these two observa- 

 tions, since the failure of plant lice to develop wings under 

 more favorable conditions may be due simply to the rapidity 

 of development of the rest of the body. After about one day 

 from the birth of plant lice, those that are to produce wings are 

 clearly distinguishable. Possibly the delay before birth result- 

 ing from a partial wilting of the plant, or possibly the short- 

 age of food for the new-born insect may give the wing buds 

 time to begin development and to reach a point where they 

 have an even chance with the other organs of the body. 



Professor Clarke has shown* that the common rose aphis, 

 Siphonophora rosac, can be made to produce wings in the first 

 generation upon rose cuttings in sand wetted with solutions of 

 magnesium salts, while nothing else tried showed any effect. 

 This is a case where there is no diminution in water supply; 

 either the wing buds were stimulated by the presence of mag- 

 nesium, or the other parts of the body were retarded. If the 

 latter is true, it would simply fall in line with the suggestion 

 made above. 



* The Journal of Technology. Vol. i. 



