SOME SOUTH INDIAN INSECTS, ETC. CHAP. XI. 



times, the number of baggings required depending on the degree 

 of infestation, and the natures oi the soil and crop. It is oi course 

 impossible to bag cereal crops when thej are grown up as it is 

 impossible to get the net sufficiently near the ground to catch the 

 hoppers and because the damage done bj the workers running 

 through tin field would be too great, but such crops may easilj be 

 bagged without damage before they have attained a growth of 

 three feet. 



The efficiency of both the hand and bag-nets may be increased 

 by soaking them with oil before use but this practic* is nol econo- 

 mically sound unless waste oil is available at a nominal i ost. 



Hopper-dozers are machines used for the control of . 

 hoppers and are made oi a series of trays, usuallj oi metal, joined 

 in a parallel series and so interspaced that each traj fits into the 

 interval between each row of a field-crop. The inside oi' each tray- 

 is painted with tar or other sticky substance or is simply filled 

 with oil and water and the machine is then dragged through the 

 infested field which, it is needless to add, must have been previ- 

 ously sown in parallel lines by means of a drill. Idle hoppers, 

 disturbed by the passage of the machine, jump or are brushed off 

 tin- plants and tail into the trays where they stick to the tar or are 

 smothered bj the oil, which kills them even it they succeed in 

 escaping from the trays. A machine of this sort was tried in Bellary 

 in connection with the Dei can Grasshopper work in tgi] and was 

 found to be quite efficient but less economical than bag-nets, whilst 

 hopper-dozers possess the disadvantage that their use is restricted 

 lo drill-sown land. As an adjunct to the use of the bag-net, when 

 the crops have become too high to admit oi bagging, hopper-do 

 maj sometimes be very useful. 



Light-traps are used to attract and kill the adults of various 

 crop-pests, especially those which are stem-borers in their e 

 life and therefore difficult to check in their directly destructive 

 Stages. They are simple in construction and inexpensive to work 

 and it i- probable that light-traps may be found to be the best 

 means of checking such pests as the Stem-borers of paddy (Sclne)IO- 

 bius bipunctifer) and of ragi {Saluria inficita). Any ordinary lamp, 

 holding sufficient oil to bum all night, may be used and is placed 

 amongst the crop, either standing in or suspended just above a pan 

 of oil and water which should project at least si\ inches on each 

 side of the lamp. file lamp should be so placed that the flame is 

 situated just above the tops of the growing i rop and that the light 

 is visible all around. A mixture of kerosine and coconut oil gives 



a good light at small cost. The lamp should be lighted at dusk 

 lefl burning all night. The insects, which are attracted by 



