Norman Cunliffe 1*29 



and 5 drying oft" would occur, with the result comparable with that 

 obtained in Exps. 14-16. 



When the soil was saturated with water and thoroughly compressed 

 by hand, the emergence was nil (Exp. 12). That emergence of the flies 

 from the buried puparia had taken place was proved by the recovery of 

 the empty puparia. When the soil was loosely sieved in and pressed on 

 top only (Exp. 11), a 40 per cent, emergence was obtained, which was 

 half that of the controls. In the series of experiments with larvae, how- 

 ever, conducted under very similar conditions emergence practically 

 equalled that of the controls. 



It will be noticed that whereas flies emerged freely from a depth of 

 6-9 inches, under normal moisture conditions (Exps. 6-9 and 11), they 

 were unable to make their way a similar distance through a dry medium 

 (Exps. 14-16), the dust from which probably choked their spiracles. 



It is probable that only fully grown larvae succeeded in completing 

 their metamorphosis, the young larvae being deprived of food owing to 

 the rotting of the host plants. 



It seems fair to conclude that ploughing-in a badly infested crop would 

 fail to control the pest effectively. Subsequent rolling, on heavy land, 

 would probably form a crust of sufficient density to prevent emergence 

 on a large scale, but not on medium or light land. 



Ploughing alone would check the development of larvae in their 

 early stages owing to the destruction of the food supply, but would have 

 to be conducted at a time when the attack would not be readily dis- 

 cernible. 



Effect of Manurial Treatment. 



Vassiliev (27) conducted some experiments in 1911 to show that the 

 application of mineral manures nullified the damage due to frit and 

 concluded that under optimum conditions, produced by the appHcation 

 of phosphorus and nitrogen, frit-fly had no marked economic influence 

 if the degree of infection was limited to 40 per cent. This experiment 

 was repeated last season in its essential features with duplicate plots 

 of area one-twelfth of an acre each, "Excelsior" oats being drilled in 

 on 4. 3. 20. Strips through the centres of the plots were examined, 

 955 being the average number of plants handled in each case. As the 

 experiment is not original, for convenience of comparison the results are 

 meaned and presented synoptically on the plan adopted by Collin (8), in 

 whose paper VassiUev's figures are quoted. 



Ann. Biol, vm 



