June 2014 Featured Paper

"Mate Recognition and Sex Differences in Cuticular Hydrocarbons of the Diurnal Firefly Ellychnia corrusca" by Qing-Lei Ming and Sara M. Lewis, Department of Biology, Tufts University. Annals of the Entomological Society of America, 103(1):128-133 (2010)
Read the Original Article

There are a number of species of diurnal, or daytime, fireflies and, unlike nocturnal fireflies, they do not use light signals to attract a mate. Studies have shown that these fireflies use volatile pheromones, chemicals that waft through the air. The male firefly follows the pheromone upwind to the female.

Ellychnia corrusca is a common diurnal firefly. E. corrusca spends the winter as an adult on the bark of trees. They become active in spring and wander over the bark in search of a mate. When a male meets a female, he first contacts her with his antennae and mouthparts before mounting her to mate. Observations of these fireflies show no evidence that the males are using volatile pheromones to locate females. Their behavior suggests that males recognize females by contact pheromones—chemicals that do not travel through the air but remain on the insect and must be touched.

Cuticular hydrocarbons (CHCs) are a group of chemicals found on the outer waxy layer of insects. Each species has its own specific group of CHCs. The CHCs function to waterproof the insect, but have also been shown to act as a contact pheromone in certain insects. This study investigates the use of CHCs as a contact pheromone in E. corrusca. Do E. corrusca males identify females as possible mates by the CHCs on their exoskeleton? If so, what specific CHC is the contact pheromone?

For the purposes of this study, a male E. corrusca was placed in a container with two females. The CHCs of one female were removed, while the other female, the control, retained her CHCs.

Mating in E. corrusca involves three steps. The first step is contact—the male touches the female with his antennae or mouthparts. The second step is mounting—the male climbs on top of the female. The third step is mating.

The researchers observed that most of the males contacted and mounted the control females, and over 70 percent mated. Although the males contacted the CHC-free females at the same rate as contact with the control females, significantly fewer mounted and none mated. These results demonstrate that E. corrusca, unlike most other diurnal fireflies, use contact pheromones to find a mate.

A study of the CHCs of both genders showed that the males and females shared most of the same CHCs, although sometimes in different concentrations. One type of CHC was found only on the female. To test whether this was the contact pheromone, females with only this CHC were presented to the males, but in no case did the males attempt to mate. The researchers conjectured that possibly this female-specific CHC acts in concert with other CHCs as the contact pheromones involved with mating choice. Also a possibility is that some of the CHCs found in both males and females but in different concentrations may act as the contact pheromones.

Future studies are needed to determine the identification of CHCs used by the males to recognize a mate.

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