PROCEEDINGS OF THE THIRD E:NT0:M0L0GICAL MEETING 485 



except to leave the whole examination alone ; it must be remembc^red 

 that nearly a quarter of a milhon bolls are dealt with annually, the 

 busiest weeks averaging 23-24,000 bolls examined. The results may 

 be summarized briefly as follows (see Table XII) : — 



Grouping together all the bolls examined throughout the season, 

 we find that group A was attacked only to the extent of 4 per cent., group 

 B to 20 per cent., group C 33 per cent. (This includes a few per cent. 

 Farias) . 



Given equal numbers of bolls of all three groups — which does not 

 occur in nature, as the large bolls predominate — we find that small 

 worms are three times less abundant in bolls of grade A than in either 

 of the two larger grades. Medium-sized worms are seven times more 

 abundant in bolls of grade B and ten times more abundant in grade C 

 than in grade A. Large worms are eight times more frequent in grade 

 B and twenty times in grade C than in A. 



Supposing our samples to have been approximately representative 

 in the proportions contained of the three grades (probably grade A is 

 however under-represented), then small worms are three times more 

 abundant in grade B and twenty-five times in grade C than in grade A. 

 Medium-sized worms are eight and eighty-six times more abundant in 

 B and C than in A, and large-sized worms nine and one hundred and 

 seventy-one times more abundant in grades B and C than in A. 



All this probably only proves that the older grades have been longer 

 exposed than the younger ones. But it is conceivable that an insect 

 might prefer young bolls to old ones ; this is not the case with the Pink 

 Bollworm. 



From an investigation made in 1917 in which the entire spoils of at 

 first 100 and later 50 cotton-plants were examined daily, the results 

 of which it is hoped will be pubhshed more in extenso elsewhere, the 

 following observations have a bearing on the same problem of the age 

 of bolls when attacked. In this case no attempt had been made to 

 grade the bolls or larvae, but attention was given to recording the traces 

 of previous occupation of a boll by worms which had left the boll, and 

 in many cases it was found that a boll containing larvse had previously 

 been attacked by others. Traces of previous occupation begin to be 

 recorded about one week after the first worms had been seen, and there 

 is a very strong correlation (0-968 ±0-015) between the attack of 

 one week and the " traces " of the next week, especially for the period 

 of eight weeks commencing 7th July and ending 31st August and 

 commencing 14th July and ending 7th September. This period is 

 selected for remark, as after that date part of the bolls showing '' traces" 

 would have ripened and no longer be recorded. 



