Tent caterpillars

Eastern tent caterpillar, Malacosoma americanurrr, whole, 1978 ... 

Beyer, W.N. and J. Moore. 1980. Lead residues in eastern tent caterpillars (Malacosoma americanum) and their host plant (Prunus serotina) close to a major highway. Environ. Entomol. 9 10-12. 

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

By June 11 all of the field load Insects had died or left the trees. Leaf damage to the test trees when measured on June 3 was relatively light. Leaves exhibiting noticeable damage averaged 27.6 i 2.1% (S.E.) for the control trees and 49.0 i 4.7% for test trees (p < 0.01, one-tailed paired t test). Estimated leaf area loss averaged 2.5 + 0.2% for controls and 11.3 i 2.1% for test trees (p < 0.005, one-tailed paired t test). Damage to control trees was due to unidentified insects other than tent caterpillars. 

Figure 1- A Average biomass and survivorship of groups of western tent caterpillar larvae fed leaves in the laboratory from red alder trees under attack by tent caterpillars in the field (---) compared to those fed leaves from unattacked con-...

The test trees were reloaded with additional colonies of tent caterpillars... 

Due to the very poor performance of the Insects in the field, as had been noted in the alder experiment above, the test trees were reloaded with an average of 8.0 1 1.0 (S.E.) additional colonies of tent caterpillars, obtained from alder, since none were available from willow, on May 22. These additional colonies were mainly in the 4th and early 5th Instar, whereas the original larvae hatched on the trees were still mainly in the third Instar. Thus, at the time of reload, the trees experienced a large... 

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. 

Tilman, D. (1978). Cherries, ants and tent caterpillars timing of nectar production in relation to susceptibility of caterpillars to ant predation. Ecology 59 686-692. 

Tent caterpillars on a cocoon, Glacier North Park, Montana. Insecticides are used to eradicate populations of such species where they are not desirable. 

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