Changes to the acoustic properties of Gromphadorhina portentosa defensive sounds when exposed to the molting hormone, 20‐hydroxyecdysone

Steroid hormones play a pivotal role in shaping arthropod phenotypes, with 20‐hydroxyecdysone (20E) serving as a key regulator of molting, a vulnerable period in an insect's lifecycle. Despite its critical role in arthropod growth and development, the influence of 20E on arthropod behavior, particularly defensive strategies, remains poorly understood. We investigated the impact of 20E on the bioacoustic characteristics of hisses in the Madagascar hissing cockroach (Gromphadorhina portentosa), a social species with multiple complex acoustic signals. With increased 20E, we predicted that hiss production would be more likely and more defensive (i.e., longer hisses with greater intensity (dB) and reduced frequency (Hz)). We injected male G. portentosa with either a low‐ (35 μg) or high‐dose (70 μg) of 20E or a control (0 μg 20E), and we measured the presence/absence of hissing responses and their bioacoustic characteristics following a standardized tactile stimulus. Contrary to our prediction, there was no difference in the likelihood of hissing or hiss duration with 20E administration. However, administering 20E resulted in reduced hiss intensity and increased hiss frequency (as measured by peak and center frequencies), suggesting potential shifts from defensive to aggressive signaling. Our study contributes to the limited knowledge of the behavioral effects of 20E, suggesting that some arthropods may experience increased aggression or energetic limitations to defense during molting. Behavioral changes elicited by hormones have important implications for both fundamental ecology and applied pest management. The steroid hormone 20‐hydroxyecdysone (20E) plays a crucial role in arthropod molting, yet its impact on behavior, particularly defensive behaviors, remains unclear. We examined how 20E influences hiss bioacoustics of Gromphadorhina portentosa and predicted that hisses would become more defensive (e.g., greater intensity and lower frequency) with 20E increases. Instead, 20E reduced intensity and increased frequency, corresponding to shifts toward aggression or a reduced energetic allocation to defense. These findings improve the fundamental understanding of arthropod ecology and possibly suggest applications.