Norman Cunliffe 125 



The lenjrth of life, under .similar conditions as to food supply, is the 

 same in summer as in spring. The presence of an abundant water supply 

 only doubles the life of the individual, whereas a plentiful food supply 

 in addition, ensures a life ten times as long. Under adverse conditions 

 the female is more resistant than the male. It has been shown in 

 Section A (p. Ill) that reproduction can take place at least 30 days after 

 emergence. 



The longevity of the fly in the field is probably very variable and 

 entirely dependent on meteorological conditions. For this reason no 

 approximation to the longevity in the field can be deduced from the 

 prevalence curves shown in Section A. 



The Value of Ploughing as a Repressive Measure. 



Collin (8) remarks that "no definite experiments, beyond those of 

 Krassilbchik and Vitkovsky mentioned under 'Pupae' appear to have 

 been made as to how far the fly can be controlled by being buried under 

 the ground in its earUer stages, especially as to whether the larva can 

 complete its feeding and pupate after the affected plant has been ploughed 

 in." 



Among the earlier authors there was some confusion of species and 

 control by ploughing was not advocated, but latterly this measure has 

 been recommended by many, e.g. Ormerod(2i) suggested ploughing 

 "with a skim-coulter attached so as to bury infested plants well down," 

 and Carpenter (6) without any apparent justification goes one step further 

 and says " it is advisable to plough a hopelessly lost crop deeply into the 

 soil, as the maggots and pupae will be killed if buried far down." 



Even recently, Sch^ziyen (24) recommends the sowing and ploughing-in 

 of trap crops "as the larvae are thus buried in the ground," although 

 Dobrovliansky (lO) had pointed out that it was necessary to roll ploughed- 

 in crops heavily to prevent emergence, having probably seen an account 

 of the experiment of Krassiltchik and Vitkovsky (16), in which they 

 found that flies escaped freely from a glass vessel containing puparia 

 covered with rammed soil, which was kept wet. Some prehminary 

 experiments on a small scale were made in 1919-20 with the view of 

 ascertaining whether the larvae could, under any conditions, complete 

 their development, if buried with the host plant. The results of these 

 experiments are given in the following synopses. 



In all cases the presence of larvae in the plants was ascertained by 

 previous examination of the stems, the control plants being treated in 

 exactly the same way. 



