[ 119] 



to 60 feet in diameter, or the entire areas of meadows, were to be seen 

 covered with yellow and dead grass the roots of which were found to 

 be full of the earth- coloured larvae of Tijmla oleracea. Grasses and 

 clovers are chiefly attacked while plants with hard or thick roots are 

 not affected. Where the infested zone borders on a furrow the larvae 

 fall into it during the night and being incapable of climbing out may be 

 collected in large numbers. They are not migratory, so that healthy 

 meadows may be found close to infected ones. Infection is due to 

 chance circumstances bringing fertilised Tipulids to the ground." I am 

 satisfied that the statement that the larvae are not migratory is erroneous 

 and that the existence of healthy meadows near them may easily be 

 otherwise explained. 



The conclusion to the experiments just described — unsatisfactory 

 as regards the object for which they were planned — was due to the 

 excessive numbers of larvae used on the plots. The large numbers 

 were decided on with a view to avoiding an indifferent result, and this 

 was supported by field experience, where large numbers had been 

 seen and which had not proved harmful. In its result, however, it 

 is useful and the possibility of migrations from waysides, waste land, 

 or grass fields to germinated com crops cannot be neglected. The 

 experience recorded on p. 12'2 may be recalled, in which a field ex- 

 amined in April, and found almost negative as regards the presence 

 of Tipula larvae, was later found to have an abundant supply. This 

 problem is under continued investigation. 



Various field experiments and observations have been made with the 

 view of testing the efiect of manurial agents and various insecticides 

 upon the larvae. One of these is quoted below, but in general the results 

 obtained were not consistent, and in cases of some well-known insecti- 

 cides were not corroborated by direct tests upon larvae in confinement. 

 The experiments were useful mainly in bringing into prominence some 

 factors which are contributing elements affecting the degree of attack 

 upon the crop, ajid which are considered in the succeeding section. 



Field Experiment : Holm, Stornaway. Oat Crop. 



In the previous season the field was grazed by cattle right on to the 

 end of November, and with sheep and cattle on to January. Ploughing 

 began early in January, and was finished by the end of February. 



