The Effect of Eastern Tent Caterpillar (Malacasoma Americanum) Infestation on Fall Webworm (Hyphantria Cunea) Selection of Black Cherry (Prunus Serotina) as a Host Tree

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ABSTRACT.-

This study determined whether the presence of Eastern tent caterpillars on black cherry affects selection of the same tree by fall webworms in the same season. Five study sites were selected, each containing 30 to 50 black cherry trees, which were marked and measured. The total number of Eastern tent caterpillar nests was counted on each tree in June 2001. Fall webworm nests were recorded as they developed throughout the summer. A logistic regression showed a significant difference (P < 0.01) in the use of previously colonized vs. uncolonized trees by the fall webworm. Fall webworms were less likely to occur on trees that had been used by Eastern tent caterpillars earlier in the season. At the end of the study period, 8.5% of the trees had been used by both species and fall webworms alone had colonized 21% of the trees observed.

INTRODUCTION

Nests of the Eastern tent caterpillar (Lasiocampidae, Malacasoma americanum) and fall webworm (Arctiidae, Hyphantria cunea) are common sights throughout most of the eastern United States and Canada. Most people are unaware that these caterpillars are distinct species, which are not closely related. They are both members of Order Lepidoptera and are classified as social caterpillars. Social caterpillars do not have the complexity of social interaction characterized by the eusocial insects such as bees, termites and ants, but they do demonstrate numerous social behaviors including aggregation, tent building, trail marking, recruitment and synchronized foraging (Fitzgerald, 1995). These behaviors make the Eastern tent caterpillar one of the most advanced of the social caterpillars. The fall webworm also displays some social characteristics, such as aggregation and tent building, but does not demonstrate more complex activities observed in the Eastern tent caterpillar (Fitzgerald, 1995; Costa, 1997).

The Eastern tent caterpillar has been studied extensively and much is known about its behavior and life cycle (Snodgrass, 1910; Fitzgerald, 1995; Costa, 1997). These caterpillars are among the first phytophagous insects to emerge in the spring, generally appearing just as leaves start to appear on the host trees. This timing is critical to survival of the larvae, as an early emergence will mean that no food is available and late emergence may mean that the leaves are too tough or mature for optimal growth. The rapid physical and chemical changes occurring in the leaves make it possible for only one generation of Eastern tent caterpillars to survive each year (Fitzgerald, 1995). The larvae can do significant damage to host trees during their brief stay, however, since they eat the new leaves which trees need for their own growth. This is especially true during years of heavy infestation.

There has been less research done on the fall webworm in the United States because the fall webworm does not have as great an economic effect as the Eastern tent caterpillar. It is a native organism in this country and consequently is kept in check by natural predators, parasitoids and other population controls. The fall webworm does pose a serious threat in other parts of the world, including Europe, China and Russia, where it was imported in the 1940s in shiploads of fruit, nuts and other botanical products (Sharov and Izhevskiy, 1988; Zhang et al., 1998). It is considered one of the most important pests of fruit, nut and shade trees in China and has the status of a quarantine pest (Zhang et al., 1998). Mulberry (Morus spp.) is one of the fall webworm's preferred host plants in these countries, making it particularly devastating to silk-producing areas (McIntee and Nordin, 1983). Because they can have more than one generation per year, they can do a great deal of damage in a single growing season. In addition, webworms are not limited to very young foliage and can use numerous tree species as hosts.

The female moth of both species is responsible for selection of host trees. …