1:34 Biitloytj <(n(l EcoikhhIc S'Hiiiifirdncc o/'Tipiila i)aliulos}i 



tested was found blank. The last four lots were from Plot 5, unrolled 

 part. Plots 1, 3, and 4, showed improvement on the crop at this date. 

 On July 14th the results showed as follows : 



Plot ] . Originally the thinnest. Recovery good. 



Plot 2. Originally 2nd thinnest. Now same as Plot 1. 



Plot 3. Originally the best. Much ahead of all. 



Plot 4. Originally only medium. Second best. 



Plot 5. Originally 2nd best. Worst of all. 



There was no very obvious difference between the once and twice 

 rolled parts of the plots, but the unrolled parts were decidedly poorer. 

 Larvae were still active in the field at this date. 



On 15th September the field was visited and the crop as ■& whole 

 found to be in a very good condition, it having tillered remarkably 

 well. The variety of oat was Hamilton. Signs of the larvae having 

 been present were scarcely apparent, any patching being extremely 

 slight. The nitrate plots did extremely well, the salt ones also were 

 very good. From the appearance of the crop in May, it would have 

 been impossible to have foreseen such an excellent recovery. Local 

 circumstances did not allow of the estimation of the yield of the 

 separate plots by weight per plot. 



Factors favouring the Larva. 



It may be regarded as well established that Tipula larvae are 

 generally distributed and ordinarily present in the soil, though not 

 necessarily only upon farm lands. Even upon these they have been 

 found to be present in appreciable numbers, when no recognisable loss 

 in crops resulted. The question of importance is, — what are the cir- 

 cumstances determining a destructive attack upon a crop? 



Naturally the first condition of importance is the presence of 

 excessive numbers. The various factors contributing to the periodical 

 appearance of large numbers of any species of insect have not hitherto 

 been appreciated in advance, and indeed cannot be said to be well 

 understood. In general with regard to Tipula they may be held to 

 include : 



(1) favourable weather conditions for the survival of the large 

 numbers of young which are generally produced : 



(2) unfavourable conditions for competitors : 



(3) ready supply of food : 



(4) absence or diminution of numbers of natural enemies. 



