June 2013 Featured Paper

"Ecology and Yearly Cycle of the Firefly Photuris pennsylvanica" by Ronald R. Keiper and Lynn M. Solomon. Journal of the New York Entomological Society, Vol. 80, No. 1 (March 1972), pp. 43-47.
Read the Original Paper (Subscription to JSTOR is required. Check your local university library for access.)

Photuris pennsylvanica is a common northeast firefly found from June to early September. The larvae are active at night, emerging from their daytime underground burrows to feed on soft-bodied insects, snails, and earthworms. They feed by injecting a digestive enzyme into their prey that liquefies the flesh, which the larvae then consume. Like the adults these larvae have two light organs on the underside of their next-to-last body segment.

This study seeks to discover factors necessary to maintain the larval maturation process, and how much those factors can be manipulated so that this species might be a useful laboratory experimental animal.

Three experiments were devised to answer the following questions:

  • Experiment 1 - Can larvae be successfully raised in the lab and retain their daily migration pattern of resting underground during the day and emerging nightly to feed?
  • Experiment 2 - Do different soil types affect this daily migratory pattern?
  • Experiment 3 - Can the time needed to rear the larvae successfully be reduced by decreasing the number of days they are exposed to each temperature stage?

Experiment 1

50 larvae were kept in a terrarium filled with loose, loamy soil and subjected to these temperature changes:

  • 48°F for 30 days
  • 42°F for 120 days
  • 37°F for 73 days
  • 75°F for 40 days until adult hatched

Only six of the 50 larvae, or 12%, successfully emerged as adults. While this number is low, it indicates that P. pennsylvanica larvae can be successfully raised in captivity.

Experiment 2

Four terraria with 50 larvae each were exposed to the same temperature conditions as in experiment 1, but each terrarium contained a different soil type: 1) loose loamy soil (control group); 2.) sand; 3.) decomposing sawdust; 4.) heavy clay-like, moisture-retaining soil.

In all three experimental terraria, a hard crust formed on the surface when the soil dried out. This crust prevented larvae from migrating between the soil during the day and the surface at night.

All but two of the larvae (from terrarium 4) perished, either from being trapped below the surface or above, where they presumably perished from the cold.

Results of this experiment indicate that P. pennsylvanica larvae thrive best in loose, loamy soil, which is where they are usually found in nature.

Experiment 3

To test whether their rate of maturation can be accelerated in the lab, larval exposure at each temperature stage was reduced as follows:

  • 48°F for 30 days
  • 42°F for 100 days
  • 37°F for 20 days
  • 75°F for 35 days until adult hatched

Nine of the 50 larvae, or 18%, successfully emerged as adults. The outcome suggests that larval development can be artificially speeded up.

An attempt was made to see if the coldest (37°F) stage applied could be eliminated. The temperature stages in this experiment were as follows:

  • 48°F for 30 days
  • 42°F for 120 days
  • 75°F for 45 days until adult hatched

Five of the 50 larvae, or 10%, successfully emerged as adults. This survival rate may be low, but still shows that the low temperature stage is not necessary for larval maturation.

Additional Observations

P. pennsylvanica larvae seem to prefer the gray garden slug (Deroceras reticulatum) to other foods offered to them. Larvae were also observed drinking juice from blue grapes.

The pupae construct an earthen chamber below the surface of the soil where they remain for 20-24 days until they emerge as an adult.

When exposed to the light of an amber pen-light flashing at one-second intervals, larvae responded with an erratic flash. This poses a question that begs further study: do the larvae possess some sort of rudimentary understanding of adult sexual communication?

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