CONTRIBUTIONS FROM THE WISLEY LABORATORY. 379 



XVIII.— ON BEANS DAMAGED BY BEETLES. 



By F. J. Chittenden, F.L.S. 



In some seasons a considerable quantity of the seed of broad beans 

 offered for sale is found to be damaged by a boring beetle (Bruchus 

 rufimanus, Boh.), often wrongly called the bean weevil. The beetle 

 is not a weevil, and as a true weevil (Sitones lineaius) is often found 

 attacking the bean foliage it would be better to call this the "bean- 

 seed beetle." The beetle is too well known to need description here. 

 Its eggs are laid in the bean flowers or on the very young pods The 

 larvae, when hatched, bore through the pod into the seed and feed there, 

 where the beetle also hibernates. The larvae rarely do any noticeable 

 damage up to the time the seeds are ready for table, but during 

 ripening burrows of a considerable size are made, though the larvae 

 seem to avoid piercing the testa. In spring, or earlier if the beans 

 are stored in a warm place, the beetles emerge and the exit holes are 

 very noticeable. 



The question often arises whether the damaged seeds may be sown 

 with a prospect of reaping a crop. It would manifestly be unwise 

 to sow the beetles as well as the seeds, and there is unfortunately 

 considerable danger of doing so, with the certainty that the next year's 

 crop will be affected. It is not very difficult to destroy the beetles. 

 The sample of seeds attacked should be placed in a vessel which can 

 be hermetically closed. A hole should be bored in the top of the vessel. 

 Immediately beneath it should be suspended a wide-mouthed basin. 

 After the beans are placed in the vessel and the latter closed with the 

 exception of the hole at the top, carbon-bisulphide is poured into the 

 basin at the rate of 3 lb. to each one thousand cubic feet of space in 

 the vessel and the hole immediately closed with a cork. The vessel 

 remains closed for about forty-eight hours, when, if it has been in 

 a warm place, the beetles will be found to be dead. 



The seeds of certain varieties of beans seem always to be attacked. 

 It is, for instance, very unusual to see a sample of ' Aquadulce ' free 

 from the pest, and this is not altogether the seedsman's fault. He 

 may perhaps be called upon to destroy the beetles before he parts 

 with the seed, but it is at present not infrequently beyond his power 

 to secure seeds free from beetle attack. 



Our own experience had led us to believe that seeds so attacked 

 gave as good results as those free from the trouble. The larvae in- 

 stinctively avoid damaging the radicle and plumule of the seed in 

 their burrowing. We have never seen either damaged by them in 

 the broadbean. Though they consume a considerable quantity of the 



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