PROPAGATION AND ARTIFICIAL INTRODUCTIONS. 91 



would enable the parasites present in the various weeds to escape 

 and attack the most abundant host, namely, the boll weevil. 



If, with all these precautions, the boll weevils are very numerous 

 in the field, and the expense is not too great, much can be gained by 

 picking the squares and placing them in cages, as has been described 

 in a previous section. 



Finally, at the proper season for haying, the actual methods of 

 cutting and preparing the hay will without doubt furnish still greater 

 control to the weevil. Some time in September, if not before, whether 

 haying is carried on or not, there should be a thorough cutting of all 

 weeds around the cotton field in order to force the parasites to the 

 boll wee^dl and also to get rid of favorable hibernation quarters for 

 the boll weeviL 



6. PROPAGATION AND ARTIFICIAL INTRODUCTIONS. 



The propagation of parasites under artificial conditions and their 

 introduction are attended with a great amount of labor and expense 

 and have many technical difficulties. The simplest form of propaga- 

 tion is the collection of infested squares at one locality and the ship- 

 ment of them to another locality, where they are placed in the field 

 to await results. There are good reasons for attempting thus to 

 introduce parasites. It has been found by very close observations 

 that the parasites are not evenly distributed, but that each species 

 has a more or less definitely defined geographical region. This is 

 no doubt due to the distribution of the normal host weevils. The 

 purposes of introduction are to take these parasites from their native 

 localities and place them in geographical regions in which they do 

 not at present exist. Definite proofs that results can be obtained 

 in this manner were to be had at Dallas on the experimental farm in 

 1906 and also in 1907. The 1906 experiment has been fully described 

 in the first report on the parasites of the boll weevil (Pierce, 1908a). 

 In 1907 a similar experiment was tried by the release of large numbers 

 of adult parasites. These parasites were carried to a field in small 

 screen cages containing foliage, so that the parasites might not become 

 overheated. The cages were opened in the shade, and the parasites 

 allowed to fly out in any direction which they pleased. While many 

 species of parasites were released in this manner, they did not all 

 show the results that were expected, but the release of Catolaccus 

 incertus in a given part of the field accomplished an increase in the 

 control in hanging squares by this species. In two other parts of the 

 field Microbracon mellitor was released, and it also showed good gains. 

 As Microbracon was released on this farm both in 1906 and 1907, it may 

 be useful to compare the percentages of parasitism at various periods. 

 In August, 1906, this species furnished 8.5 per cent parasitism in hang- 



