84 Swede Midge in parts of Yorkshire 



rutabaga, Mr Taylor has found the following plants to be attacked by 

 the Swede Midge: 



Brassica napus Turnip. 

 B. rapa Rape. 



B. oleracea Cabbage. 



B. sinapis Charlock or Wild Mustard. 



Raphanus sativus Radish. 

 R. raphanistrum Wild Radish. 

 Turnips I have found by observation to be attacked only to a very 

 small extent. Rape occupies an area small compared with that of 

 swede crops. Cabbage and Radish occupy a very small acreage com- 

 pared with that of swedes. Wild Radish is not a very abundant weed, 

 but Charlock is found in plenty. 



Bezzi and Kertesz in their Catalog. Palaearc. Dip. give as host plants 

 of the Midge, 



Nasturtium palustre Marsh Watercress. 

 N. silvestre Creeping Watercress. 



These plants are found in wet situations in Holderness, but whether 

 they are attacked there by the Midge I cannot say. 



The relation of the Midge to wild hosts is a question which I have 

 not yet investigated. But on p. 94 I explain why I believe wild hosts 

 are not of much importance in determining the abundance of the 

 Midge in a district. 



III. Methods. 



Swedes are grown in rows which are from 24 to 28 inches apart, 

 and in singling the plants are left about 12 inches apart. It is therefore 

 perfectly easy to count the number of swedes in a row. It is also quite 

 easy to tell at a glance which plants have been attacked. Moreover, 

 the maggots spend the whole of the feeding period within a very short 

 distance of the point where the eggs were laid. They do not move from 

 one plant to another. And the distortion brought about by the Swede 

 Midge can easily be distinguished from that caused by other insects. 

 As Mr Taylor says (p. 12), the leaves "retain to the end discoloured 

 traces of the injury, and since the crumpled character persists, it follows 

 that the observer can readily recognize, by their leaves, swede plants 

 that have been attacked by the Midge, although neither flies, eggs, nor 

 larvae may be present." I did, of course, come across plants which I 

 was not able to say with certainty had or had not been attacked, but 



