Role of cuticular hydrocarbons and social cues in mate recognition and copulatory behavior of ladybird beetle, Cheilomenes sexmaculata (Fabricius)

The efficiency of insects in finding a suitable mate is crucial for their reproductive success. Chemical communication is primarily used to search for and recognize a potential mate. At close range, cuticular hydrocarbons (CHCs) are known to serve as mate recognition cue. In this study, we assessed the role of CHCs and social cues in mate and sex recognition through behavioral assays in ladybird beetle, Cheilomenes sexmaculata. To examine the role of CHCs in sex and mate recognition focal males were exposed to alive males and females and CHCs washed females (immersed in chloroform for 5 min, 30 min and 24 h) respectively. For social cues, males were made to encounter alive as well as dead males and females. Their copulation attempts and mating parameters (time to commence mating and copulation duration) were recorded. We also assessed whether males only mounted the dead females or copulated with them (i.e., transferred ejaculate). Our results revealed that focal males showed higher copulation attempts with alive individuals, regardless of sex. However, they attempted copulation with dead females significantly more often than with dead males. Washing of CHCs significantly influenced copulation attempts, with unwashed beetles showing a 100% attempt rate, followed by those immersed in chloroform for varying durations. Males initiated mating sooner and engaged in longer copulation with alive females compared to dead ones. Although, males mounted and copulated with dead females, no difference in sperm transfer was observed compared to alive females. Our study demonstrated that CHCs along with social cues (such as movement), play a pivotal role in eliciting male copulatory behavior.