Predicting Defoliation by Pine Processionary Caterpillar, Thaumetopoea wilkinsoni (Lepidoptera: Notodontidae) in Young Pinus brutia Plantations in Northern Cyprus

摘要

A method is described for predicting severity of defoliation of young Pinus brutia plantations ( 50% of the branches defoliated and/or larval colonies present This rating system provides a range of individual tree and plot ratings from 0 to 6 depending on the severity of defoliation. Results Timing of egg-mass surveys Initial screening of the data from sample plantations in which egg-mass surveys were conducted in early October had higher larval colony counts than egg-masses. Recounts of egg-mass numbers in these plantations during early December indicated that more egg masses were found in December. October egg-mass counts ranged from 33 to 94.2% of the egg masses found in December (Table 3). This discrepancy in egg-mass counts was believed to be the result of three possible scenarios: 1. October egg-mass surveys had been conducted before adult flight and oviposition were completed. 2. Egg-masses produce more than one larval colony. 3. Field crews did not detect all egg-masses present. Table 3 - Percentage of Pine Processionary Caterpillar Egg Masses Detected by First Egg-Mass Sample, Five-Finger Mountains, Northern Cyprus, 2002 If this discrepancy was due to egg-mass surveys being done before adult flight was completed, the greatest discrepancy between the two sets of egg-mass counts should have occurred in the low elevation plantations where adult flight and oviposition occurs later than at the high elevations (BUXTON, 1983). However, comparison of the proportion of egg-masses detected in October by elevation failed to show a clear trend (Table 4). It is, therefore, believed that the discrepancies between the October and December egg-mass counts are the result of all three factors listed earlier. Egg-mass counts taken in December were used in the analysis. Table 4 - Percent of Egg Masses Detected by First-Egg Mass Sample, by Elevation Zone, Five-Finger Mountains, Northern Cyprus, 2002 Data ranges The average number of egg-masses/tree for the 30 sample plantations ranged from a low of 0.20 to a high of 4.23. These were lower than the values obtained for the two plantations sampled in 2000. Larval colony densities per tree ranged from 0.20 to 4.49. Estimates of larval colonies were higher than estimates of egg-masses/tree in 11 of the sample plantations (Table 5). Table 5 - Distribution of Sample Plantations by Egg-Mass and Larval Densities, Five-Finger Mountains, Northern Cyprus, 2002 Estimates of precision Estimates of numbers of egg-mass densities per tree was within ± 0.5 egg-masses/ tree 95 out of 100 times in 25 out of the 30 sample plantations and within ±0.69 egg masses on the remaining sample plantations. This was considerably higher than the expected precision of ± 2 egg-masses 95 out of 100 times based on the data collected in 2000, especially considering that none of the sample plantations contained the recommended number of 50 sample trees. This is believed to be due to higher numbers of egg-masses on individual sample trees in 2000. One of the trees sampled in 2000 had 45 egg-masses (Table 1). This is probably unusual and adversely affected the estimate of sampling error. In 2002, the highest egg-mass count obtained on a single tree was 15. The precision of estimates of the numbers of larval colonies per tree was similar to the estimates of egg-mass densities. In 25 of the 30 sample plantations, estimates were within 0.5 larval colonies 95 out of 100 times. In the remaining five plantations, the estimate was within ±0.67 larval colonies/tree. Egg-mass/ Larval colony/ Defoliation correlations Regression analyses using the linear model y = a + bx (FREESE, 1978) was made for three relationships: 1. Egg masses/ tree (x) vs. early instar larval colonies/ tree (y) 2. Egg masses/ tree (x) vs. defoliation rating (y) 3. Early instar larval colonies/ tree (x) vs. defoliation rating (y) Each of these models showed a strong positive correlation between the dependent and independent variables with correlation coefficient