Academic journal article The American Midland Naturalist

Studies of Ballooning and Resulting Patterns of Locally Contagious Distribution of the Bagworm Tyridopteryx Ephemeraeformis (Haworth) (Lepidoptera: Psychidae)

Academic journal article The American Midland Naturalist

Studies of Ballooning and Resulting Patterns of Locally Contagious Distribution of the Bagworm Tyridopteryx Ephemeraeformis (Haworth) (Lepidoptera: Psychidae)

Article excerpt

ABSTRACT.-A series of field studies was stimulated by the unexpected finding of a band of junipers (Juniperus virginiana) bearing heavy infestations of bagworms, the band running south-southwest to north-northeast through a woodlot (near Norman, OK) of otherwise lightly infested trees. Fidelity to wind direction was confirmed, and numbers of bagworms ballooning from 3.05 m to 36.58 m was measured, with Tanglefoot(R) traps mounted on metal fence posts. Ballooning numbers were satisfactorily described with a negative exponential model incorporating both gravitational and trap losses. No significant difference was found between ballooning distances achieved by larvae with and without early-stage bags. A study of infestation levels on ornamental junipers planted around houses on the north and south sides of east-west streets revealed both a strong front- vs. backyard difference, and a weaker but statistically significant side-of-street effect. Patterns reflecting short-range dispersal were found in a linear windbreak planting of northern white cedar (Thuja occidentalis), and in a 12 X 44 = 528-tree lattice of planted junipers (near Urbana, Illinois). A "bonfire" effect showing heaviest infestations in mid-lattice, and reduced infestations on the periphery (especially on the windward edge) was postulated and confirmed. Studies of the effect of increased "target" size of larger trees, and of the incidence of apparent bird and small mammal predation, are also reported.

INTRODUCTION

The unusual life history of the bagworm Thyridopteryx ephemeraeforzs has been described in varying detail by numerous workers (e.g., Kulman, 1965; Kaufmann, 1968; Morden and Waldbauer, 1971; Sheppard and Stairs, 1976; Furniss and Carolin, 1977; Lance and Barbosa, 1979). Its life history is remarkable in several respects, notably for the bags that the larvae construct around themselves, and continue to enlarge throughout larval life. The larvae attach fragments of foliage from the host tree to their bags, these fragments becoming larger on average as the bag itself is enlarged (Ghent and Larson, 1964). Larval bags have "turtleneck" openings at the upper and larger end for feeding, and at the smaller (i.e., earliest constructed) lower end from which the frass is expelled. Larvae extend the head and thorax from the upper end of the bag while crawling and feeding. The head and thorax are pigmented and chitinized, but the abdomen-which always remains within the bag-is not. Both males and females pupate in late summer within the larval bags. Winged adult males seek out bags still occupied by the wingless females. Mating is achieved by the male inserting his abdomen into the lower opening of the female bag. The female oviposits within her bag, usually filling much of the bag cavity-including her cast pupal skin-with eggs. The spent females then drop to the ground, the eggs overwintering in the female bags. Escape from their bags by the winged males is achieved by the male pupae first wriggling down to the lower opening, from which they protrude before the pupal skin splits. This permits the males to fly free without damage to wings and antennae during egress from the bag. This is an instance of adaptive behavior by what are technically still pupae, although the pupal movements are presumably achieved by male near-adults, otherwise ready for eclosion.

Bag-bearing T.ephemeraeformis larvae are capable of limited dispersal by crawling, but their awkward bags restrict this to movements of a few meters between neighboring trees. Ballooning by neonate larvae on silk threads is the only effective method of dispersal of the species over greater distances. Barbosa et al. (1989) note this same reliance on ballooning in 13 additional species of female-flightless Lepidoptera in eastern North America, and Hackman (1966) discusses the association of flightlessness and ballooning in 19 families worldwide. The same association is the focus of Harrison's (1997) study of the western tussock moth (Orgyia retusta), and of the study by Rhainds et al. …

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