Experiments with T. viridana larvae were made in order to investigate, whether there are differences in food quality between leaves of Quercus robur and Quercus petraea.
These experiments were conducted in the Federal Research Centre for Forestry and Forest Products, Großhansdorf (Germany). The results presented in Figure 9 and 10 are based on data from 137 larvae, which were separately fed with either leaves of Q. robur or Q.
petraea.
Figure 9: Food needed for lar-val development, calculated into amount of tree leaf-loss. Feeding damage of one bud is counted as a loss of six leaves.
Figure 10: Duration of larval de-velopment, from egg hatching un-til pupation, on Q. robur and on Q. petraea for both male and fe-male T. viridana.
Figure 9 shows the amount of leaf-loss for Q. robur and Q. petraea trees, which is caused by a single T. viridana. The given values are the sum of bud-damage of early larval stages and leaves eaten in later stages. One damaged bud is calculated as a leaf-loss of six leaves.
This is the average number of leaves growing out of one bud.
There is a very high variation in the amount of leaves that have been eaten by a single larva, the mean value is about seven leaves per individual. No significant difference in the average amount of leaf-loss was found between both sex and oak species. However, the variances between Q. robur and Q. petraea were significantly different (Levene’s test, p<0.05). This could be a hint that the substantial composition of Q. robur has developed a greater variability through co-evolution with its herbivores.
Figure 10 shows the duration of larval development on Q. robur and on Q. petraea for both male and female T. viridana. There is a significant difference between the mean duration of larval development between females and males and also between larvae on Q.
robur and on Q. petraea. It is known that T. viridana larvae are proterandrous. This could be validated, as in our experiments male larvae pupated earlier than females as well (ANOVA, p<0.001). There is also a significant difference in mean duration of development between Q. robur and Q. petraea (ANOVA, p<0.01). This indicates substantial differences between these two oak species and also a different susceptibility as fodder plants for T.
viridana.
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