Aggregation, courtship, and behavioral interactions in European earwigs, Forficula auricularia L. (Dermaptera: Forficulidae)

Due to its relatively cool, humid summers, southwestern Virginia provides an ideal climate for European earwigs, Forficula auricularia. In 1990 - 1992, nymphs were captured in wooden groove-board traps beginning in late May, adults were captured beginning in mid-June, and disappeared from sampling sites by September or October. Sex ratios were significantly female-biased most of the season, becoming more marked by the fall. The pest status of F. auncularia is exacerbated by its gregarious nature. Gas chromatography-mass spectroscopy and accompanying behavioral bioassays showed that aggregation occurred as a result of a pheromone located on the male cuticle, which is probably a minor component of the hydrocarbon profile. Approximately 88% of the detected volatiles on the cuticle were identified as a series of normal and branched alkanes. Fatty acids and hydrocarbons were also identified in nymphal and adult legs, but these extracts were not attractive. Frass, which also contained fatty acids and hydrocarbons, was attractive, but likely acquired its attractancy through the earwigs' proclivity for consuming carcasses and exuviae. The defensive quinones produced by F aunculana repel conspecifics. A study of the behavioral repertoire of F. aunculana showed that, contrary to previous reports, only nymphs are nocturnal. Many differences in behavior were due to gender, age, and partner age. (e.g., females spent more time feeding than did males, adults fed more when paired with nymphs than when paired with adults). Social behaviors (communal feeding, aggression, contact, and dorsal palpation) comprised <10% of the insect's behavioral repertoire.

Since dorsal palpation, a previously undescribed behavior and a form of allogrooming, occurred more frequently during reproductive periods, it may have a sexual significance. Dorsal palpation also may augment the distribution of defensive quinones on the cuticle of F. auricularia. An analysis of nymphal group dynamics demonstrated that as group size increased, nymphs spent significantly less time feeding alone and grooming, but more time resting. Antennal contact rates between group members increased significantly with group size. Detailed observations of the courtship and mating of F. auricularia revealed a complex of sexual behaviors for both males and females. Receptive females were behaviorally active during courtship. The significance of the male cerci was demonstrated by their use in early courtship with displays, and later use as a tactile stimulus for the female; and study of males from which the cerci had been removed, which showed no mating by amputated males. Male forcep length was bimodally distributed and positively allometric, while female forcep length was normally distributed. Males with longer forceps did not have a mating advantage. Further research is needed to identify the chemical composition of the aggregation pheromone, and to quantify any advantages of body and forcep size on mating success.