PREVIOUS WORK WITH INSECT PARASITES. 



21 



Fig. l.—Polygnotus hiemalis, a parasite of the Hessian fly: Adult. 

 Greatly enlarged. (From Webster.) 



portation from one part of the country to another becomes easy, since 

 all that has to be done is simply to collect twigs bearing the scales, 

 preferably during the 

 winter months, and 

 carry them to non- 

 protected regions, 

 the parasites being 

 dormant and pro- 

 tected each by the 

 scale of the coccid 

 which it had de- 

 stroyed; and it was 

 specifically recom- 

 mended that the im- 

 portant parasite of 

 the black scale (Sais- 

 setia olese Bern.), de- 

 scribed in the article 

 as Tomocera califor- 

 nica, could be readily 



carried from California and utilized to destroy Lecanium scales 

 in the Southeast. 



Excellent work in this direction has been done of 

 late years by the Bureau of Entomology. In the study 

 of the Hessian fly (Mayetiola destructor Say), under 

 Prof. F. M. Webster, early-sown plats of wheat at 

 Lansing, Mich., and Marion, Pa., in 1906, were very 

 seriously attacked by the Hessian fly, but when ex- 

 amined carefully at a later date fully 90 per cent of the 

 flaxseeds (pupae) were found to have been stung by a 

 hymenopterous parasite, Polygnotus Tiiemalis Forbes 

 (figs. 1, 2), and to contain its developing larvae. A 

 field of wheat near Sharpsburg, Md., was found to be 

 infested by the fly, and examination indicated the ab- 

 sence of the parasite. On April 8, 1907, a large num- 

 ber of the parasitized flaxseeds from Marion, Pa., 

 were brought to Sharpsburg and placed in the field. 

 On July 8 an examination of the Sharpsburg field 

 showed that the parasites had taken hold to such an 

 extent that of the large number of flaxseeds taken and 

 brought to the laboratory for investigation not one 

 was found which had not been parasitized. Additional 

 material secured from Sharpsburg in the spring of 1908 

 in the same locality showed all of the Hessian flies to be parasitized. 

 In the same way excellent results have been obtained in the investi- 

 gation of the cotton-boll weevil, under Mr. W. D. Hunter. In the 



Fig. 2.— Polygnotus 

 hiemalis: Adults 

 which have de- 

 veloped within 

 the " flaxseed " 

 of the Hessian 

 fly and are ready 

 to emerge. Much 

 enlarged. (From 

 Webster.) 



