Codling Moth1 Egg Distribution on Unmanaged Apple Trees2

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Abstract
During the summer of 1975, the distribution of colding moth (Laspeyresia pomonella (L.)) eggs, infested apples, and branch structures were recorded for sample branches from an abandoned orchard near Pullman, Washington. Distribution of eggs within trees was analyzed at 3 levels: (1) among spurs, (2) within particular spur classes, and (3) on leaves. Among spurs, the distribution of eggs deviated from randomness in relation to all spurs, fruit-bearing spurs alone, and individual apples. Within particular spur classes, distribution of eggs fit negative binomial but not Poisson distributions, indicating nonrandomness. Occurrence of eggs on individual leaves also deviated from a Poisson distribution. Avg numbers of eggs per spur were positively related, and avg numbers of eggs per apple were negatively related to the numbers of apples per spur. Fifty-seven % of all eggs were found on upper leaf surfaces, 35% on lower leaf surfaces, and 8% on apples, but these percentages were not constant over the summer. Eggs were aggregated around apples; 51% were within 7.5 cm, and 91% were within 20 cm. The scattered distribution of codling moth eggs is advantageous since it reduces predator pressures and limits multiple attacks on individual fruits. These advantages probably outweigh the observed disadvantage of high mortality during larval searching.