22 B.C. Entomological Society. 



infestation. If it is possible to examine tlie objects without injuriug them in any- 

 way, and it is wished to follow the observations by others during the same season 

 to obtain the progress of infestation, stakes or markers should be used, so that the 

 same area or ground is covered each time. The number of insect injuries that can 

 be examined in this way are necessarily limited, but we find examples in the 

 stinging of fruits, etc., by such insects as the curculio, capsids, sawflies, and so on. 

 Progress of infestation can, however, be obtained, when the objects are destroyed, 

 by frequent examination within a certain area. Results then can only be gauged 

 by charting the notes obtained and general survey taken over a greater or lesser 

 period of time. 



Let us take the instance of a field of turnips affected with the root-maggots 

 (Pegomyia, (Pliorbia) hrassiew). If before thiuning we pulled up fifty young plants 

 in each of five locations in the field and examined for maggots and their injury to the 

 roots, and noted it in the following manner, viz. : — 



North Out of 50 plants, were infested. 



South 50 ., 7 



Centre 50 „ 8 



East 50 „ 10 



West •. 50 „ 9 



Total Out of 2.50 plants, 34 were infested. 



Then 13.6 represents the percentage of infestation. 



Determinations of this nature can be made the basis of many series of observa- 

 tions and experiments, and the details can be arranged to suit the requirements of 

 the case at the discretion of the inspector. 



To estimate the egg, larval, or adult abundance to an acre when the insect or its 

 stages are observed, we first must know the lineal feet of row per acre. The follow- 

 ing table, therefore, is compiled, derived by division of the number of square feet per 

 acre — viz., 43,5G0 — by the width of the row : — 



Rows in Running Feet 



Feet apart. per Acre. 



2V2 17,424 



3 14,520 



3% 12,445 



4 10,890 



414 9,680 



5 8,712 



5% 7.920 



6 7,2G0 



6% 6,701 



7 6,222 



7% 5,808 



8 5,445 



9 4,840 



10 4.356 



11 3,960 



12 3,030 



15 2.904 



IS 2,420 



20 2,178 



30 1.452 



40 1,089 



To put this table into application, let us suppose we wish to determine the egg- 

 abundance of the cabbage-maggot {Pegomyia (Phorbia) brassica;} in a field of turnips, 

 the adult abundance of the strawberry-root weevil (Otiorhynchns ovatus), the adults 



