Abstract
The antennae of adult male German cockroaches detect a contact sex pheromone embedded in the female’s cuticular lipids. The female pheromone stimulates courtship behavior in males, notably a wing-raising (WR) display. Within aggregations, however, cuticular lipids are disseminated by contact among group members, including nymphs and adults of both sexes, and “contamination” of cockroaches with the cuticular lipids of another stage or sex may interfere with sex discrimination and disrupt courtship. We used behavioral observations, bioassays and chemical analysis to determine how males maintain their sensitivity to sex pheromone in aggregations. Males contaminated with female pheromone displayed lower courtship, because residual female pheromone on their antennae adapted their peripheral sensilla and habituated the central nervous system. Female pheromone that contaminated the male’s antennae also elicited courtship from other non-contaminated males, disrupting their sex discrimination in the group. However, antennal grooming effectively removed female pheromone from males’ antennae and maintained their chemosensory acuity and sexual discrimination among group members. Thus, grooming of the antennae and other sensory appendages is an important strategy to enhance sensory acuity, especially in group-living insects like the German cockroach.
Highlights
Insect cuticular lipids, composed mainly of relatively non-volatile apolar lipids, cover the insect cuticle and serve as barrier that prevents desiccation and penetration of harmful agents including pathogens[1]
The recognition that antennal grooming is important in eliminating environmental contaminants from insects[16,17,18,19,20,21], and recent evidence that antennal grooming prevents a build-up of cuticular hydrocarbons (CHCs) that can interfere with olfaction[22], prompted us to consider this behavior in male-female interactions
The frequency of antenna grooming was significantly higher than that for other body parts during the scotophase, while no significant differences in the grooming frequency among body parts were observed in the photophase (Fig. 1C) (ANOVA and Tukey’s HSD: Early photophase, df = 3, F = 0.229, p = 0.876; Late photophase, df = 3, F = 1.535, p = 0.219; Early scotophase, df = 3, F = 9.27, p < 0.01; Late scotophase, df = 3, F = 3.13, p = 0.035)
Summary
Insect cuticular lipids, composed mainly of relatively non-volatile apolar lipids, cover the insect cuticle and serve as barrier that prevents desiccation and penetration of harmful agents including pathogens[1]. The German cockroach is a gregarious insect, and courtship is commonly observed in crowded aggregations that contain both sexes and various developmental stages in close proximity, frequently touching each other’s antennae to maintain group cohesion[14]. This group-living arrangement may cause inadvertent exchange of cuticular lipids among individuals, possibly compromising the effectiveness of the sensory system that makes sex recognition and discrimination possible. We determined whether grooming frequency of German cockroach male antennae increases during behavioral activity, including courtship. We discuss the importance of grooming for chemosensory behaviors in group-living insects
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