October 2016 Featured Paper

"Chemical Egg Defense in Photuris Photinus Firefly ‘Femme Fatales’" by Andrés González, James F. Hare, and Thomas Eisner.
Chemoecology 9:177-185 (1999)
Read the original article (free subscription to ResearchGate needed)

Photinus fireflies contain two types of defensive chemicals: betaine, which they produce themselves, and lucibufagins (LBs), which they acquire from eating male Photinus fireflies. This study examines the endowment of these two chemicals to the Photuris eggs and their effectiveness in deterring predation by insects.

In this study, female Photinus were raised in the lab from larvae. As adults they were not fed Photinus males in the lab, and so had not acquired the lucibufagins they need for their eggs. Half of these Photinus females were then fed Photinus males. Eggs were collected from both groups of female Photinus. Eggs collected from those that had fed on Photinus males were labeled (+) eggs, and the eggs from the females not fed Photinus males were labeled (-) eggs.

Upon examination, females that had fed on Photinus males and their (+) eggs contained both betaine and LBs. The female Photinus that were not fed Photinus males and their (-) eggs contained only betaine.

An experiment to determine the effectiveness of betaine and LB in deterring predation by insects followed. Both the (+) and (-) firefly eggs along with moth eggs coated with either betaine or LB were offered to three insect species: the Asian ladybug, the black ant, and the European earwig. The results are listed in the following chart:


Asian ladybug larva Black ant European earwig
(+) Photuris eggs Strong deterrent Strong deterrent Partial deterrent
(-) Photuris eggs Strong deterrent Strong deterrent Partial deterrent
Betaine-coated moth eggs Strong deterrent Strong deterrent Not a deterrent
LB-coated moth eggs Strong deterrent Strong deterrent Partial deterrent

The researchers next took clusters of both (+) and (-) firefly eggs and the betaine- and LB-coated moth eggs and placed these clusters in the field to check for predation. The number of eggs remaining was counted every two days for a period of ten days. The results indicated that the (+) and (-) eggs were predated on equally. Both the betaine- and LB-coated moth eggs were also predated on, but to a lesser degree than uncoated control eggs.

The researchers concluded that both betaine and lucibufagin contribute to the distastefulness and protection of the eggs. Neither compound, however, provided complete protection against all predators, but by endowing her eggs with both compounds, the female Photinus maximizes the protection afforded.


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