Cecidomyidae 397 



remove all soil particles, and then placed in wide-mouthed bottles of 200 

 cc. capacity, containing about 150 cc. of the water culture. One plant 

 was placed in each bottle, the roots being immersed in Pfeffer's plant 

 food solution,* and the stalk, kept in position by being held lightly 

 against one side of the neck of the bottle with a cotton stopper. 



The plants grew well in this solution. The growth of algae in the 

 liquid was largely overcome by painting the bottles black. Usually the 

 plants lived long enough for experimental purposes without changing the 

 liquid. When the experiments were prolonged the solution was changed 

 as often as necessary. 



By using this method, it was possible to follow the life history of the 

 Hessian fly from oviposition to the formation of the puparium. The 

 plants could be handled conveniently and the various stages studied with 

 greater ease and exactness than when the plants were grown in the soil. 

 When necessary, the plants could be removed from the bottle and placed 

 under the binocular for close study. By carefully shaving the epidermis 

 of the leaf sheath, it was possible to keep the larvae under observation 

 at all times. As the larvae increased in size they could readily be seen 

 through the neck of the bottle. 



This method proved so successful in the Hessian fly work that it was 

 adopted for the study of a number of other insects infesting cereal crops: 

 chinch bug (Blissus leucopterus), green bug (Toxoptera graminum) and 

 corn leaf aphis (Aphis maidis). 



Certain modifications in the method of handling the plants were 

 necessary for these insects. In order to confine them on the stalks of 

 the plants, a small cell was formed in one side of the cotton stopper. 

 The cotton fibers served as effective barriers in holding the insects in 

 the cell and exact data could be obtained on molting and the length of 

 the instars, and, in the case of the aphids, on the number of young 

 produced. This method was also used to study certain phases of activity 

 of several parasites of the Hessian fly puparium. The parasites were 

 confined in the cells and their behavior and methods of oviposition were 

 easily observed. In a similar manner a study was made of the chinch 

 bug egg parasite (Eumicrosoma bene fie ia). 



Reference 



For the culture of other members of this family see p. 266. 



♦Pfeffer's solution: 



Calcium nitrate 4 grams 



Potassium Nitrate 1 gram 



Magnesium sulphate 1 gram 



Potassium dihydrogen phosphate. 1 gram 



Potassium chloride 0.5 gram 



Ferric chloride trace 



Distilled water 5 Hters 



