Tent caterpillar attack, willow

Responses of Alder and Willow to Attack by Tent Caterpillars and Webworms ... 

Thus, in contrast to the results obtained the same season with alder, no differences were found in tent caterpillar growth or survival when fed leaves from attacked versus control willows. 

Figure 2. Top normalized average relative growth rates of groups of western tent caterpillar larvae raised in the laboratory of leaves from test, nearby control, and far control Sitka willow trees. The test trees were loaded with tent caterpillar colonies on the indicated date. Bottom density of tent caterpillar larvae attacking the...

On the other hand, no differences were found in growth or mortality of tent caterpillars fed leaves from unattacked willows compared to those fed leaves from willows attacked by tent caterpillars (Figure IB). Reload of the attacked trees with additional tent caterpillars coincided with a rapid decrease in biomass and an increased mortality of Insects fed leaves from both attacked and unattacked control trees. This could have been by chance, but it suggested the possibility that both attacked and control trees exhibited a rapid decrease in food quality in response to the addition of more insects to the attacked trees. If so, this suggested that unattacked willows were sensitive to signals from nearby attacked willows or the attacking Insects. An experiment to test this hypothesis produced positive results (Figure 2). 

Tent caterpillars fed leaves from willows attacked by tent caterpillars grew more slowly than larvae fed leaves from nearby and far controls 11.5 days after the initiation of attack. Three days later, larvae fed leaves from both attacked willows and nearby controls grew more slowly than larvae fed leaves from the far controls. No evidence was found for root connections between willows of the same age as the study trees at the same site. 

The burden of proof for such an unprecedented effect should be high, and the foregoing experiments with willows and tent caterpillars cannot be considered to constitute such proof. However, at the very least, they show that the results of experiments designed to test for changes in leaf quality of attacked plants should be Interpreted with caution, particularly if control plants are near attacked ones. 

Responses of alder and willow to attack by tent caterpillars and webworms evidence for pheromonal sensitivity of willows. In Plant Resistance to Insects, ed. 

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