186 CATERPILLAR PESTS. 



escapes notice as it is a small one and the large second brood is so 

 abundant that hand-picking becomes a difficult business. 



In some instances it is possible to shake the caterpillars to the ground 

 and crush them. When the caterpillars hide in the ground by day-light, 

 cultivation between the plants exposes them to birds and kills many. 

 The same is true when they have entered the ground and become chry- 

 salides. This is always necessary when the field is badly attacked, as 

 a large number of chrysalides will probably be found there. 



On low crops the use of the bag (page 72) is advisable, large numbers 

 being swept up. As a preventive measure one must do everything 

 possible to stimulate the rapid and healthy growth of the plant ; a strong 

 vigorous plant that is putting out many leaves can stand far more than 

 a weak unhealthy one. 



The practice of sowing mixed crops has an influence on leaf -eating 

 caterpillars and the mixtures sown especially on small irrigated areas in 

 the dry hot weather are almost necessary if the main crop is to be estab- 

 lished. The caterpillars which are very prevalent in these crops, attack 

 a subsidiary crop which can be rooted out, leaving the main crop well 

 established and healthy. Occasionally it is possible to use another crop as 

 a trap for caterpillars, which then do not injure the main crop. Thus 

 sorghum and maize are valuable in certain areas in cane fields and the 

 value of bhindi as a trap for pests of cotton is being tested. Such plants 

 must be used with caution. If allowed to grow too long they first 

 attract pests from outside and then transmit them to the main crop, 

 becoming breeding places for undesirable insects which when abundant 

 leave them. The essence of a trap crop is to destroy it with the insects 

 on it at the' right moment. Birds are extremely valuable as checks on 

 leaf-eating caterpillars and anything which encourages such caterpillar- 

 eating birds as, mynas is useful. The growing of roadside trees has a 

 very special value in this connection, especially when these trees are such 

 as mynas frequent, and the cultivator's practice of putting branches of 

 trees in an infested field of paddy so that the insect-hunting birds 

 may come and perch there is a shrewd one. The common hen is 

 a valuable ally in gardens and small cultivation, but she requires 

 some food besides caterpillars and must not be left to feed exclusively 

 upon them. 



In most cases one of the above precautions can be applied success- 

 fully and when all else fails, an application of insecticide can be resorted 

 to if the crop is worth it. For small areas of vegetable crop and for small 

 irrigated patches, the tin sprayer and a dose of kerosene emulsion does 

 all that is required ; if the caterpillars are large, lead arseniate may be 



