304 Insect and other Invertebrate Fauna 



2. One of these plots (plot 2) has received 14 tons of farmyard manure 

 per acre per annum since 1843; the other (plot 3) has received no manure 

 of any kind since 1839. This difference in treatment had a very marked 

 effect on the number of insects present. 



3. T'wenty-three samples of soil were examined from each plot, each 

 sample being a cube 9x9x9 inches. The soil in each sample was 

 removed in five layers, so that it was possible to determine the approxi- 

 mate depth at which the specimens occurred. 



4. There were, in round numbers, 15,100,000 invertebrates per acre, 

 of which 7,720,000 per acre were insects, in plot 2, and 4,950,000 inverte- 

 brates per acre, of which 2,470,000 per acre were insects, in plot 3. 



5. The greatest number, both of insects and of other invertebrates, 

 occurred in the upper three inches of the soil, but some species were found 

 in larger numbers at a greater depth, the greatest number of Elateridae 

 larvae being found at a depth of five to seven inches, and of Symphyla 

 at a depth of seven to nine inches. 



6. Some species, such as the larvae of Chironomidae and Trichocera, 

 were practically confined to the plot which had received farmyard manure, 

 plot 2, while other species, such as the CoUembola, Onychiurus amhulans 

 and 0. fimetarius, although they occurred in both plots, were consider- 

 ably more numerous in plot 2. 



7. Injurious insects, such as the larvae of Elateridae, Tipulidae and 

 Hepialidae, appeared to be little affected by the different manurial 

 treatment of the two plots, and occurred in practically equal numbers 

 in the two plots. 



8. Although 198,653 and 164,983 Elateridae larvae per acre occurred 

 in plots 2 and 3 respectively, they did not produce any appreciable 

 effect on the crop. 



9. An attempt was made to estimate the amount of nitrogen con- 

 tained in the bodies of the soil fauna, and it was found to be 7349-6 gm. 

 or 16-2 lbs. and 3409*2 gm. or 7-5 lbs. in plots 2 and 3 respectively. It is 

 unlikely that there is any appreciable loss of nitrogen from the soil due 

 to the migration of winged members of the fauna. 



10. The worms, insects and insect larvae are beneficial in loosening 

 the soil and facilitating aeration and drainage. 



11. The net results of these observations show that, although the 

 introduction of farmyard manure greatly increases the invertebrate 

 population of the soil, the latter organisms are saprophagous and are 

 not directly injurious to the growing crop. Such injurious organisms as 

 are present occur in approximately equal numbers whether the land be 



