396 niOCEEDINGS OF THE THIED ENTOMOLOGICAL MEETING 



gnaw the surface and do not kill it themselves, fungal diseases follow. 

 When fungal diseases affect the base of the stem usually the entire cane 

 dries up. The borers in the grown cane itself, observed at Pusa in the 

 course of the last two seasons, did not prove to be serious. They are 

 the same which infest the young shoots. They do not however occur 

 in large numbers in individual plants and one or two caterpillars in the 

 stem of a grown-up plant are not able to kill it or retard its growth 

 seriously, although a single larva is sufficient to kill a young shoot. 

 Besides, they seem to prefer young shoots to grown-up canes and, as 

 there are plenty of young shoots always in the field, the majority of 

 the grown canes escape being attacked. The tunnel of the borers in 

 the stem always opens externally and, affords access to fungal diseases, 

 which in extreme cases may cause the upper part of the cane to dry 

 up. The effect of fungal diseases in grown canes is observed to be slow. 

 Sometimes the tunnel of the borers may run across the stem in such a 

 manner as to cause it to break at that point or to stop further growth 

 above it. When growth stops in this manner vigorous plants put forth 

 side shoots (PI. 68, f. 1 «, c, d). The effect of attack at the top by 

 Scirpophaga caterpillars is always to stop further growth and the 

 plants may either wither from the top downwards or put forth 

 side-shoots (fig. 2 and fig. 1 b). No other borer attacks grown canes 

 at the top. 



The planting of cane is usually done about February and the greatest 

 injury to the crop is caused by the borers in the young stage and up 

 to about July. By this time some plants are grown and become partly 

 immune, the harvest being obtained principally from these plants. As 

 will appear from records of actual observations given below of two 

 varieties of thick canes, viz., Purple Mauritius and Sathi No. 131, on 

 the average, out of every four shoots which grow only one comes to be 

 harvested, the other three being killed at various stages of growth, 

 mainly by the injurious activities of insects and fungal diseases. All 

 thick varieties seem to be Hable to a similar amount of damage. Thin 

 varieties are however more resistant. A rough idea of the comparative 

 immunity of thick and thin varieties may be formed from column 6 

 in Table V giving the number of harvestable canes out of every 100 

 setts planted. 



The experiments of 1917. 



In November 1916 a plot | acre in area in Chaunia field at Pusa was 

 planted with Purple Mauritius. In Table I, the percentage of affected 

 plants, including dry ones as well as those with " dead heart," and 

 the proportion of the agents of damage are shown. 



