MINISTRY OF AGRICULTURE, EGYPT. 



Bulletin No. 24. 



ON THE DISPERSION OF THE PINK BOLL WORM 



IN EGYPT. 



Ever since statistics have been kept relating to the attacks of the 

 pink boll worm it has become increasingly evident that the distribution 

 of the larvce in time and space, i.e. through the growing season of the 

 cotton, through the cotton aiea and in the individual bolls making 

 up the cotton crop, must follow definite rules. 



In the following an attempt has been made to find out the mode of 

 distribution of the worms in the bolls. 



The problem of distribution of worms into bolls is not the same as 

 the classical problem of throwing balls into holes, but is a much more 

 complicated one. Some of the new factors which must be considered 



are : 



(1) The moth when laying her eggs exercises to a certain extent 

 selection, as can be seen from the fact that flower-buds are not selected 

 unless there is a shortage in the supply of suitable green bolls. 



(2) The eggs are frequently laid in batches, not always singly. 

 However, the mortality of the hatching worms appears to be sufficient 

 to eliminate irregularities arising from this source, whereby the exact 

 position on the boll where the egg was placed is of importance. 



(3) The time element, carrying with it fluctuations in both the 

 boll population and the worm population. It must be remembered 

 that infestation only takes place during the growing period of the 

 boll, whilst it is still green. This period lasts about seven weeks 

 (fifty days) from the setting to the opening of the boll. During this 

 time two things are happening : the absolute abundance of moths 

 and with it the chances of infestation are increasing, and the supply of 

 bolls is varying. Each boll is advancing towards maturity, and 

 every succeeding night is again exposed to the risk of infestation. 

 It ought thus to be obvious that bolls just set, and consequently 

 exposed for one or few nights only must be much less attacked than 

 older groups. Bolls of the same age have been exposed to the same 

 extent as each other, each night they are old contributing one -fiftieth 



