Rabu, 27 Maret 2013

Biology of the Firefly Pyractomena lucifera

This study details the biology, ecology, and flash behavior of Pyractomena lucifera, a firefly that lives in freshwater marshes throughout the eastern half of the United States. In particular, the firefly is common in the marshes around Lake Alice on the campus of the University of Florida, where the study was conducted. There, the main plants were cattail, sawgrass, and water hyacinths. Researchers also conducted experiments in the lab.
Here, we take a closer look at their findings, through all phases of the P lucifera's life: larvae, pupae, and adulthood.

Biology of the Larvae

During the day, larvae are found in crevices between the leaves. At night, they can be seen by their glow as they move over the vegetation. The larvae are abundant in and around cattail stands as well as the throughout the water hyacinth mats. They spend most of their time near the surface of the water, but they are also found higher on the vegetation when it was wet — after a rain or in the morning dew.
The larvae were observed crawling in and out of the water — the only known U.S. firefly to do so. Experiments to demonstrate their ability to survive under water showed that they could survive submerged for 31 days, even though they have no special organs for breathing underwater.
The larvae feed primarily on snails, but also were seen to prey on freshwater limpets, spiders, a damselfly nymph, and a leech. The larvae feed both above and below the water. When they capture a snail below the water, they would pull it above the water to feed. The larvae spend considerable time patrolling the water to detect prey, occasionally sticking their heads underneath the surface.
The larvae attack snails by climbing onto their shells and reaching under them to bite and chew the flesh. Unlike reports of L. noctiluca , which inject a toxin into the snail and wait for it to take effect before starting to eat, P. lucifera showed no such hesitation, biting and chewing at the same time.

Biology of the Pupae

When the larvae are ready to pupate, they glue their tail ends to the substrate — usually hanging head down, about an inch to a foot above the water. Pupae of Pyractomena differ from that of other fireflies in three ways:
  1. They pupate on vegetation instead of in the soil.
  2. They are colored to match the vegetation instead of milky white.
  3. They do not glow when agitated.
Tests showed that the pupa stage lasts about six days at room temperature.

Biology of the Adults

Male flashing begins about a half hour after sunset and lasts for 15 to 30 minutes. At dusk, the males fly among the vegetation or slightly above it, but after dark, they fly only above it, up to six feet high.
Males produce a single flash of about 0.21 seconds, repeated every 2.9 seconds at 75 degrees and 5.1 seconds when the temperature is 62.6. Females respond from the vegetation with a single flash of about 1 second with an afterglow of several seconds. The female flash follows the male flash by 0.7 seconds at 80.6 degrees and 1.5 seconds at 62.6.
After receiving a response flash from a female, the male hovers and flashes before landing. Males then climb up and down the vegetation in search of the female, flashing at irregular intervals, with the female occasionally responding to these flashes. Once mating starts, it can last 24 hours or more.
Females can lay eggs up to five times over a 20 - 30 day period, with decreasing amounts of eggs laid each time — producing 67, 28, 19, and 15 eggs in the first four batches.
In the lab, females lived up to 53 days while the males an average of 20 days. However, in the wild, males appear to live only 11 - 12 days.

Natural Enemies

Researchers observed only a few natural enemies. These included a wolf spider, giant water bug, tree frog, orb weaving spider, and a harvestman. Interestingly, no Photuris females were seen to capture P. lucifera , even though they were common in the area.

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