360 mOCEEDINGS OF THE THIKD E>"TOiIOLOGlCAL MEETING 



out in the Insectary. A zinc cylinder with a solid bottom was filled to a 

 depth of a little more than a foot with earth which was carefully examined 

 before being put in. Six perfectly healthy sugarcane shoots with the 

 setts from which they grew and of the age at which they were observed to 

 be attacked by this insect in the field were transferred into this cylinder 

 and eleven mole-crickets introduced into it between 13th and 15th 

 March. The characteristic " dead heart " with the characteristic damage 

 appeared as early as the 17th March in one shoot. Another shoot 

 exhibited " dead heart " and damage on 3rd April. On the 12th April 

 five pumpkin chips w^ere buried in the earth and two of them were found 

 on the next day to have been bored. The buried pieces were removed 

 on the 15th April and a few fresh pieces were placed on the surface of the 

 earth. On the 17th April they were observed to have been bored 

 from below. The pumpkin chips were removed on the 19th April. On 

 the 5tli May a third shoot was damaged. The remaining three shoots 

 were not damaged and the insects were dead before the 30th May. 



This experiment seems to prove that the mole-crickets cannot live 

 on sugarcane alone. They attack sugarcane if it is planted in the land 

 in which. they are present. There was practically no damage to sugar- 

 cane by this insect in the Chmmia field which has been under cultivation 

 for many years. The experimental plots of sugarcane in the Brick- 

 field in 1918 were situated in a piece of land brought under cultivation 

 about five or six years ago. It was previously a waste land overgro'yj'n 

 with Sacchanim sfontaneum and Im/perata anmdinacea and was bordered 

 by similar waste lands. (See Plate 69.) Mole crickets have been observed 

 to eat Sacchanim sfonianeum ^oots in the same way as they do sugar- 

 cane shoots. As proved by rearing in the insectary, they can live on 

 animal food and probably depend on such food principally. Many kinds 

 of soft-bodied Melolonthid, Chrysomelid and Curculionid grubs are known 

 to abound among Saccharvtn spontanevm roots. Therefore mole-crickets 

 obtain plenty of food in such waste lands and would naturally occur 

 there in large numbers. This explains why so much damage was done 

 to the experimental plots in the Brickfield. The occurrence of this 

 insect in the sugarcane in Jhilli field in 1913 was under exactly similar 

 conditions. Sugarcane was grown again in Jhilli in 1918 but so much 

 damage was not done by this insect as on the former occasion. Repeated 

 cultivations for a series of years naturally kill and drive away the mole- 

 crickets from the field. 



Beetle-grubs. 



Among the third class of external agents of damage we have included 

 the Melolonthid, Chrysomelid, Curculionid and Elaterid grubs and may 



