Tent Caterpillars in Northern Arizona above 6000 Foot Elevations
Extension, College of Agriculture & Life Sciences, The University of Arizona
Tom DeGomez, Associate Agent, Agriculture and Natural Resources
Tent caterpillars are common insects in northern Arizona
forests as well as in urban trees. The species that can be found in northern
Arizona are the forest tent caterpillar Malacosoma disstria, sonoran tent
caterpillar M. constrictum, southwestern tent caterpillar M. tigris, and
western tent caterpillar M. californicum. They are similar in habit and
appearance. Hosts of tent caterpillars in northern Arizona include, oak,
willow, poplar, birch, ash, apple, apricot, cherry, plum, currant, and
Tent caterpillars feed upon developing buds, and young and
mature leaves of their host. It is common for trees defoliated early in
the growing season to re-leaf and fully recover from feeding damage. Death
of mature trees is rare from these pests. Young, newly planted trees,
though, may not have enough root reserves available to sustain heavy defoliation.
Extra care should be taken to protect these young trees from extensive
Indirect effects occur when tent caterpillar populations
become high and the insects become a nuisance. People in parks or in their
yards, when sitting or picnicking under infested trees, do not enjoy having
the insects fall out of the trees and land upon them and their food. Avoidance
of these spots may be the most reasonable solution.
Figure 1. Tent caterpillar larva.
Most tent caterpillars have similar life cycles and habits.
They overwinter as fully developed embryos in the eggs. They hatch about
the same time as the leaves and flowers begin to develop on the host tree.
The young larvae begin to feed as soon as they emerge (Fig. 1). They form
a tent or pad of silken threads (Fig. 2). The tent or pad is used for
resting and for protection from predators and severe weather. The larvae
feed gregariously in the early instars and alone during the later instar
stages, at which time they consume the majority of leaf material. They
feed for four to six weeks, then form a cocoon in which to pupate. They
spend approximately two to three weeks in the cocoon. Upon emergence as
adults, they mate and lay eggs on live twigs in masses of up to 200 eggs.
The egg masses, grey to brown in color, can be found from mid-summer until
the following spring.
Figure 2. Mass of silken threads of
the tent caterpillar
The embryos mature for several weeks into first instar larvae
but eclose. The larvae remain in the eggs until the following spring.
Depletion of leaves due to over population of caterpillars
may result in starvation and death, a major factor in population dynamics.
Many parasites, predators and diseases attack tent caterpillars and provide
population management. Western tent caterpillar eggs are parasitized by
wasps of the Eulophidae family and the mature larvae are parasitzed by
wasps in the Braconidae family (Johnson and Lyon, 1991). Forest tent caterpillar
can be parasitized by flesh flies of the Sarcophaga genus in very high
numbers (Johnson and Lyon,1991). Eggs, larvae, and moths are eaten by
birds (Furniss and Carolin, 1977). Very high mortality can be caused when
the nucleo-polyhedrosis virus infects the population. Fungi in the Entomophthora
genus can be pathenogenic to forest tent caterpillar (Johnson and Lyon,1991).
The biocontrol agents Bacillus thuringiensis (Bt) var. kurstaki
and var. berliner provide excellent control of tent caterpillars. Bt is
a naturally occurring bacterium that will cause paralysis within the gut
of immature insects in the family Lepidoptera (moths and butterflies);
no other group of organisms is affected. Due to the specific nature of
this pesticide, it is very safe to apply. Bt can also be mixed with nucleo-polyhedrosis
virus for control of the western tent caterpillar.
Mechanical methods can be effective in controlling tent
caterpillars on small trees and shrubs. Physical removal of egg masses
and the caterpillars from the trees can greatly reduce their numbers.
Egg masses are best removed during the winter when they are easily spotted.
The caterpillars are best removed during the early instar stage while
they are feeding in a group and utilizing the tent or pad.
There are many chemical insecticides registered for the
control of tent caterpillars, but use of chemicals is recommended only
in instances where high value trees are heavily infested and other management
tactics have failed. For currently registered chemicals consult with your
local county Extension office or with a pesticide sales person.
- Furniss, R.L. and V.M Carolin. 1977. Western Forest Insects. U.S.
Department of Agriculture Forest Service, Miscellaneous Publication
- Johnson, W.T. and H.H. Lyon. 1991. Insects That Feed on Trees and
Shrubs, 2nd Edition. Comstock Publishing Associates, Ithaca, New York.
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by the University of Arizona.
Document located http://cals.arizona.edu/pubs/garden/az1249/
Published April 2002
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