Insects and us 



with the crude slaughter of insects by sprays, and if it is successful the 

 control is likely to be lasting : but in the short view, to get a financial 

 return in a particular year, it is often simpler just to spray. 



Damage to Produce in Storage 

 When a crop has been harvested it is often stored for months, or even 

 for years, before being used, and while it is in storage it is liable to be 

 attacked by insects. A particular crop may suffer as much damage from 

 insects while it is stored as it did while growing in the field (Fig. 74). 



Damage to stored produce is not so immediately obvious as that to a 

 growing crop, because the produce is often in bales or other containers, 

 or stored in bulk in a grain-elevator. Because of the bulk and weight 

 it is difficult to inspect for insect damage, and any method of sampling 

 may easily miss pockets of infestation. 



Insect damage to a growing crop may be offset by the vitality of the 

 plant. A crop of strong plants, under good cultivation, may grow away 

 to become immune to further attacks by a particular insect, and may 

 even recover to some extent from attacks already made. Damage to 

 stored produce cannot be retrieved. Moreover, if a growing crop is 

 damaged this merely means that the farmer does not get as big a yield 

 as he hoped : only in extreme cases, Hke the coconut moth we have men- 

 tioned is the loss hkely to be complete. On the other hand stored produce 

 has already a cash value, and every ton destroyed by insects is a direct 

 monetary loss. 



Estimates of the amount of the loss naturally vary greatly, according 

 to the crop and to the climatic conditions under which it is stored. It has 

 been said that up to 50% of the corn stored on North American farms 

 may be destroyed by insects in some seasons, while many stored pro- 

 ducts suffer losses of more than 10%. The value of the stored grain lost 

 annually in the U.S. is estimated at more than 500 million dollars, but 

 the actual loss in practice is likely to be more than this. When a stock 

 of grain has suffered damage by insects what is left has a lower market 

 value, and some batches are likely to be scrapped entirely, because it is 

 not worthwhile to sort out what is useable. 



Insect damage to stored produce can be reduced, partly by prevention 

 and partly by cure. Preventive measures are improved methods of 

 storage to expose the produce less to insect invasion, and more thorough 

 clearing up of the debris between one batch and another. Once the in- 

 sect infestation is present the produce may be fumigated with poisonous 

 gases, or treated with sprays, dusts and smokes. The great problem is 

 to find chemicals that are effective against the inseas, and yet do not 

 make the produce harmful for human or animal consumption. 



125 



