Oak defoliation and population density relationships for the gypsy moth (Lepidoptera: Lymantriidae)
1991
Williams, D.W. | Fuester, R.W. | Metterhouse, W.W. | Balaam, R.J. | Bullock, R.H. | Chianese, R.J.
In 18 yr of observations on the population dynamics and defoliation of the gypsy moth, Lymantria dispar (L.), in New Jersey, percentage defoliation increased at the beginning of an outbreak, usually reached highest levels in the year before the peak population, and declined rapidly thereafter. In linear regression analyses, egg and egg mass density explained considerable amounts of variation in subsequent defoliation; the addition of a variable for population trend (i.e., the ratio of egg masses per hectare in the present year to that in the previous year) further improved the r(2). Use of a sigmoid function to model the relationship resulted in r(2) values of 0.65-0.67. Because variability was high at intermediate population densities, patterns of defoliation and population trend were explored further. Overall, defoliation in a given range of density was significantly higher when the trend was stable or increasing than when it was decreasing. The use of these results in making management decisions is discussed.
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