98 Swede Midge in parts of Yorkshire 



appeared and on searching the soil four months later I found 99 dead 

 maggots. Lack of moisture in the soil is therefore a probable source 

 of loss. 



The hoeing up in singling of plants harbouring small maggots must 

 surely be a source of loss, though maggots are able to extricate them- 

 selves from plants left lying on soil, and quite small maggots are 

 able to pupate successfully, though, of course, they turn into small 

 flies. But I find that the proportion of small maggots which pupate 

 successfully is lower than the proportion of larger maggots, and that 

 such small flies contain fewer eggs than larger flies although the eggs 

 in both are about the same size. 



The Midge has some enemies. An Empid fly which sucks the juices 

 from the flies was common at Garforth in June 1914. Some Midges 

 are accounted for by small spiders. And in September 1914 in some 

 experiments I reared a number of Proctotrypid flies from Swede Midge 

 maggots. 



In 1912 in the East Riding the competition of the Turnip Flea 

 Beetle, Phyllotreta nemorum, was a matter of some importance. The 

 Flea Beetle attacks the seed leaves of swede plants while the Midge 

 does not attack them until they get into rough leaf. In 1912 the Flea 

 Beetle was rampant in the East Riding and often made it necessary to 

 sow two or even three times. 



One more conclusion may be drawn from a comparison of the figures 

 for the different years. If it is not already possible it probably would 

 be possible after a few years further work to foretell, roughly, before 

 the first brood makes its appearance, the sort of attack which may be 

 expected. In 1911 the Midge increased enormously in number and the 

 first brood of 1912 was a very large one. In 1912 the numbers of the 

 Midge were greatly reduced and the first brood of 1913 was a very 

 small one. In 1913 the Midge increased in number, but did not make 

 much progress, and the first brood of 1914 was by no means numerous. 

 If it is the weather which is the chief factor responsible for these ups 

 and downs of the Midge, then weather statistics alone for a summer, 

 without actual observations in the field, would probably be enough to 

 enable one to make a more or less accurate prophecy of what sort of 

 attack to expect. Unless winter weather is of much importance, and 

 there has not been a severe winter since I first became interested in 

 the Midge, it would be possible to make this prophecy six or eight 

 months before the first brood appeared. 1 have already pointed out 

 (p. 90), however, the possible complication which may be introduced 



