TWENTY-EIGHTH REPORT OF THE STATE ENTOMOLOGIST 9 



During the last two years a general correlation has been noted 

 between the intensity of the infestation and the percentage of the 

 predicted bait which is used. When the per cent infestation (the 

 per cent of cropland which may need baiting) in a country is low, 

 the bait usage is correspondingly low, and when the per cent in- 

 festation is high, much more than the predicted amount may be 

 used (figure 2) . This general observation led to the compilation of 

 data in an endeavor to ascertain the inclusiveness of this correlation 

 in counties exhibiting all variations in percent infestation. The per 

 cent infestation for all infested Montana counties, together with the 

 per cent of the predicted bait used, was tabulated for 1937, 1938, 

 1939, and the north-central counties for 1940. The per cent infesta- 

 tions were averaged in 10 per cent groups, and the per cent of pre- 

 dicted bait used, on this basis, is given in the table below: 



Per Cent Infestation No. Times Occurring Per Cent of Prediction 

 Use d 



to 9.9 17 88.3 



10.0 to 19.9 31 70.8 



20.0 to 29.9 34 110.9 



30.0 to 39.9 14 139.8 



40.0 to 49.9 8 231.9 



50.0 to 59.9 6 523.7 



60.0 to 69.9 1 136.0 



70.0 to 79.9 



80.0 to 89.9 1 486.0 



The progression calculated in this table appears superfically 

 to be satisfactory until the 60.0 per cent to 69.9 per cent group is 

 reached. This group and the ones following include so few samples 

 that no significance could be attached to them. It is likely that a 

 larger number of samples in the first three groups would bring the 

 percentage of predicted bait which was used lower than those given 

 above. 



While there seems to be a good correlation between these two 

 factors when averaged in 10 per cent groups, the data indicate a 

 great deviation on both sides of the mean, and it will take more data 

 than are at hand to put this correlation on a sound basis. 



In order to discover the effect of climate and geography on this 

 correlation, the data were compiled for counties west of the Divide. 

 During the period under study these counties consistently used less 

 than the predicted amount of bait regardless of the per cent infesta- 

 tion obtained from the survey. 



If this study has a value it will be in allowing an intelligent 

 change in the method of calculating the amounts of bait needed. It 

 should indicate the amount of correction necessary in different 

 ecological habitats infested with injurious numbers of grasshoppers. 

 It may necessitate a division of the chronically infested areas re- 



