4.8i PKOCEEDIXGS OF THE TniRD ENTOMOLOGICAL MEETIXG 



to 75 per cent, is partly due to decrease in number of green bolls avail- 

 able accompanied by an increase in the actual Pink Bollworm popula- 

 tion. 



As an illustration of the fact that the greatest Pink Bolhvorm 

 population does not exist at the time of the highest percentage of infes- 

 tation some figures obtained in 1917 may be quoted. In this experi- 

 ment the average* green boll population for 100 cotton-trees has been 

 recorded for each week from that commencing on 9th June onwards 

 until that starting on 13th October. In this case the greatest number 

 of attacked bolls observed in any week was found in the week com- 

 mencing 15th September when 580 out of a total 908 bolls or 61 per 

 cent, were attacked. In the last week, when 92 per cent, of the bolls 

 were infested, there were only 59 bolls to be attacked. (Plate 86.) 



According to the percentage infestation figures, 1918 was better 

 than 1917, by at least one week. Whether this would correspond to 

 a real improvement in the crop or not depends on the comparative 

 dates of ripening of the crops for the two years. (See Plate 86). 



One point comes out quite clearly to my mind. Any method by 

 which the cotton crop can be rendered more early will iiafallibly place 

 the maximum of green bolls in a more secure position, in other words 

 will reduce attack. Two ways present themselves as leading to this 

 result, either the production by selection of an earher-maturing variety 

 of cotton, or making existing varieties mature earlier by cultural means. 

 The new cotton is still wanting, but the cultural method has 

 been devised and experimented during three seasons by Mr. Cartwright, 

 Inspector of Agriculture in Gharbia Province. The method consists 

 mainly in judicious withholding of water at a time when normal jDractice 

 is giving the plants more than they need. The result is a gain of two 

 or three weeks on the surrounding crops, with a considerable gain in 

 the harvest. Incidentally it may be mentioned that a gain of about 

 3 weeks would eliminate loss of at least 10 per cent, of the crop. 



In 1918 an attempt was made to obtain some information, whilst 

 exannining bolls for percentages of infestation, to obtain evidence as 

 to the age of bolls when attacked. For this purpose all the bolls were, 

 before examination, graded in a boll-grading macliine which automati- 

 cally sorts them out according to their sizes into three groups. Grade 

 A, bolls less than li cm. in diameter ; Grade B, bolls over H cm. and 

 less than 2 cm.; Grade C, all larger bolls. At the same time the worms 

 were recorded as small {i.e., less than 5 mm. long), medium (5 to 10 mm.) 

 or large (over 10 mm.). There appears to have been no difficulty in 

 the great majority of cases in apportioning the worms to their proper 

 class. The method is admittedly crude, but there was no alternative 



