385 



and it is more than possible that the borer caterpillars are carried on 

 to the young cane by wind. The experimental plots at the station 

 showed that the infection in adjacent cane-fields extended from 75 

 to 100 yards from the old cane, occasionally much more. The Diatraea 

 adult does not appear to fly more than about 200 yards. No data 

 are forthcoming as to the other species but their length of flight is 

 beheved to be much greater. The position of the cane-fields with 

 regard to prevaihng winds may be important, but the evening wind 

 often blows in exactly the reverse direction to that of the morning, 

 so that some modification of the system of planting would probably 

 do away A\ath this altogether. The life of the cane itself is also 

 important. The variety of sugar-cane commonly grown in Java, 

 stands at least 13 months on the ground, so that it is a common practice 

 to plant at intervals of three months ; this plan, for the reasons 

 above stated, favours continuous infection and the practice of not 

 thoroughly clearing the ground when the cane is cut, assists materially 

 in maintaining it. The use of the tops of the canes as sets is strongly 

 condemned, as these are often full of borer eggs, and the sprouting of 

 the sets only provides fresh food for the caterpillars. Another common 

 source of infection is the distribution of egg-masses, which are knocked 

 off the old canes and distributed over the borders of a young plantation 

 close by in the process of handhng, and also on the trimmings of the 

 cane sets which are left lying about ; every care should be taken in 

 cutting cane to destroy all egg-masses, and to burn all fragments of 

 cane bearing them. Yet another source of infection is found in other 

 food-plants of the borers and especially " glagah " {Saccharum spon- 

 taneuni). Diatraea and Chilo will also attack maize ; no proof has 

 yet been obtained that any of the species attack bamboo. Collection 

 of the eggs is very useful but the scattered eggs of Olethreutes escape 

 this process. Rewards for eggs collected have been tried, but it was 

 found that two-thirds of those brought in were not the eggs of borers, 

 but consisted largely of those of Aleurodes longicornis and A. hergi, 

 as well as eggs of spiders and Spodoptera sp. ; the natives even manu- 

 factured egg-masses which were stuck on to pieces of leaf with gum 

 and required more or less careful examination before the fraud could 

 be detected. Carefully organised and systematic search of young 

 plantations for eggs, by men who can be trusted, and who have been 

 trained to the work, appears to be the really practical method, but it 

 is costly and must be pursued incessantly, as the hfe of the borers is 

 short, and a whole plantation must be examined at least every four 

 days, especially those parts which are immediately adjacent to old 

 canes. This method has proved successful in the experimental cane 

 fields of the station, but, even there, it was difficult to eif ect a thorough 

 examination. Usually the first caterpillars are found one month after 

 planting, and the search for eggs should be begun a httle before this. 

 Cutting out the attacked shoots to kill the caterpillars is another 

 method of control, but as this may mean removing 40 per cent, of 

 them, the direct loss is very serious. Spraying is not recommended, 

 in as much as the cane grows very quickly and the form of the plant 

 makes effective wetting almost impossible, especially near the top. 

 The operation would also require repetition every three or four days, 

 so that it would be very costly both in labour and material. Trials 

 of Paris green and lead arsenate proved them to be qmte useless, as 

 (0172) D 



