File:Annual report (1938) (18431104941).jpg

Title: Annual report
Identifier: annualreport19381943ento (find matches)
Year: 1872 (1870s)
Authors: Entomological Society of Ontario; Ontario. Dept. of Agriculture
Subjects: Entomological Society of Ontario; Insect pests; Insects
Publisher: Toronto, The Society
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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ENTOMOLOGICAL SOCIETY 59
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i 10 20 30 10 36 20 30 4 8 2 10 20 30 5 71 to 20 j 0 25 ' 50 75 100 Figure. 1.—(a) Eight years, 1931 to 1938, catches of codling moths in bait pails, (b) The first brood as a percentage of the total catch is represented by gaps in the lower heavy black line. The figures above each gap indicate, omitting the first three figures, the year of occurrence. second as happened in 1932. A variant of this occurred in 1934 when first and second broods were equally large. (2) A very high first brood may be followed by a very small second (1931), and (3) alternately a very low first followed by a high second brood (1933). No simple correlation be- tween the weather and these brood fluctuations has been found and it is felt there must be other important factors. Were weather factors alone responsible we should not expect the fluctuations of broods to follow the regular sequence noted below. If the first brood in each year be taken as a percentage of the entire catch for that year and in each year be marked off on a line one hundred units in length (Fig. 2) a peculiar grouping is at once apparent. The eight years fall into three distinct groups with a 20 per cent, gap between them. It is unlikely that the first brood would be only 10 per cent, or lower and the second consequently 90 per cent, or over so that it is improbable that any first or second brood would fall near the ends of the 100 per cent line. With the line thus reduced at its extremities there should be more significance in the grouping along the remainder. An even more peculiar arrangement comes to light when we take the years in chronological order. Thus 1931 had a high first brood, 1932 a medium, 1933 a low, 1934 a medium, 1935 high, 1936 skipped the medium stage and went on to low, 1937 skipped back to high and 1938 regained the original cycle by reaching medium. As mentioned above weather can hardly be solely accountable for these fluctuations—they are too regular. Broods and Heredity.—What factors are responsible for a large second brood in this locality ? As a general statement it may be said that any con- ditions favouring an early peak of maturing larvae will also favour a large second brood because a high percentage (85-90 %) of the early maturing larvae transform and give rise to a second brood. As the season advances the percentage drops steadily and fairly regularly, until mid-August when it is usually less than one per cent. In rearings over a number of years it

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