( M \l\ XI. I ["HE CONTROL OF INSECT i'HSTS OF CROPS. 85 



But the plan is sound from the agricultural view-point of the vary- 

 ing requirements of different plants as regards the constituents oi 

 plant-food available in the soil and the inter-relationships of the 

 bacterial and protozoal fauna of the soil. There is no doubt also 

 that, it suitable mixed crops are grown, the increase of pests in 

 each one is reduced, such reduction, in th drill sown 1 



at least, being probabh largelj mechanical and due directly to the 

 fact that each area under one crop is separated from the next 

 similar area bj a harm crops which are not suitable 



food-plants for the pests of the former; a mixed crop of groundnut 

 and cumbu, tor example, generally shows a much lessened attack 

 on the former by the sunil-puclii (Aproarrema nerteria) as compared 

 with that suffered by an unmixed crop of groundnut. The extra 

 exposure oi the moths when egg-laying and of the immature 

 ;es when hunting for more food undoubtedly forms a direct 

 cluck on their increase. Experiments on the growing of mixed 

 mid bi carried out from .1 combined view-poinl of agri- 

 cultural, chemical, entomological, mycological and bacteriological 

 knowledge, and such experiments would doubtless proved great 

 value in obtaining increased yields. 



Ploughing i^ <>i course an ordinary practice of agriculture hut it 

 i- often no less effective in the control of insect-pests ; but for this 

 end the ordinary country plough, which generally barely scratches 

 the surface of the soil, is ol little use and we require an iron plo 

 capable of turning up the soil to a depth of at least six inches. 

 The egg-masses of grasshoppers are usually deposited a few inches 

 under the soil and many caterpillars (e.g., Kumblipuchis) also enter 

 the soil to pupate and these egg-masses and pupa; often lie under- 

 ground for months throughout the dry weather until the rains 

 awake them to new life ; if. therefore, the soil is thoroughly ploughed 

 up at this time and large clods are broken as far as possible, most 

 ol these egg-masses and pupa: will either be brought up to the 

 surface and killed by the sun or devoured by insectivorous animals 

 or they may be buried so deeply that they are unable to emei 

 at the proper time, and perish. Here again agriculture and p 

 control go hand in hand, tor ploughing during the dry season not 

 only helps to check pests but, by providing a line surface mulch, 

 moisture is conserved to the subsequent benefit of the crop. 



Changing the time of planting or of harvest when this can be 

 done, either by sowing earlier or later, or by using early or late- 

 maturing varieties ol crop, maj sometimes be used with mutism as 

 a control-measure in certain kinds of attack by insect-pests. \ 

 pest which appearsat a particular time of the year, for example, 

 maj sometimes be defeated by delaying sowing until after its 



