Table of contents

July 2000 - Volume 84 - 7

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Cover illustration: Spots before your eyes The polyphemus moth (Antheraea polyphemus) is a large North American moth with a wing span of 100-130 mm. This member of the Saturniidae family in the Lepidoptera order is generally cinnamon coloured with a large eye spot on each wing and subtle pink borders on its inside wings. Although it is the only species of Antheraeato occur in North America, it is relatively common and widespread. The eye spots, best seen when the wings are fully spread, are protective and presumably resemble an owl's eyes. These ocellated wings are thought to be an evolutionary protection against predation. Several North American owls, including the great horned owl, long eared owl, and screech owl have yellow eyes with black pupils which closely resemble the eye spots on the lower wings of Antheraea polyphemus. When disturbed, the moth will open its wings showing these eye spots as a defence mechanism. This will give an appearance of a rather large animal peering directly at the predator.   Another closely related Saturniidae moth, Hyalophora cecropia, is the principal species being investigated for a class of compounds known as cecropins. These short chain peptides, which appear to be highly conserved over many divergent animal species, are generally known to be in the group of defence peptides that include the defensins in mammals and magainins in frogs. These lytic peptides are induced by microbial agents and are capable of membrane perturbation, resulting in bacterial cell lysis. These short chain peptides appear when the moth overwinters as a cocoon and must protect itself using only a humoral system of defence. The cecropins are the "gorillamycin" of the animal world. They are effective agents against almost all bacteria, enveloped viruses, many fungi, and perhaps even certain protozoa. These compounds offer great hope and promise as a powerful agent fashioned by evolution against almost any microbial agent. Interestingly enough, the only bacterium known to be resistant to the cecropins is Bacillus thuringiensis. Empirically, this bacterium has been used as a pesticide without completely understanding why it is useful. Since it is resistant to the humoral defence of many insects, one of its mechanisms of attack on these insects is almost certainly the ability to remain indifferent to their defence systems.

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