Trade-off Investment between Tonic Immobility and Mate Search in the Sweetpotato Weevil, Cylas formicarius (Coleoptera: Brentidae)

SIMPLE SUMMARY: Tonic immobility (TI) is considered as an important anti-predator strategy. In order to know the relationship between TI and mating behavior, we investigated the cost–benefit between TI and mate search in the sweetpotato weevil (SPW), Cylas formicarius. In this study, we used Y-tube olfactometer and determined that male mate searching increase after 3 h at night. Then, we confirmed that TI was affected by mate search in the males. Because the duration of TI of the male during mate search was significantly shorter duration than the males from the control. However, TI does not affect mate search in the females. Finally, the Y-tube olfactometer was used to compare the duration of mate search and the proportion of orientation towards the females in two artificial selection groups of the male SPWs. In this experiment, we found that mate search was affected by TI. Our study results provided a clear evidence that there is a trade-off between mate search and TI behavior in males of the SPW. Further, we quantified investment of anti-predator behavior and mating behavior by measuring the duration of TI and mate search in the SPW. We believe, these methods can be useful to determine the cost–benefit between anti-predator behaviors in the prey(s) and predator(s) in other species too. ABSTRACT: Tonic immobility (TI) is a well-known anti-predator strategy adopted by diverse preys. Numerous studies on the cost–benefit involve in TI have been reported. Although, some studies have reported the effect of mating behavior on TI, few studies highlight the phases of mate search. In the present study, we investigated the relationship between mate search and TI behavior in the sweetpotato weevil (SPW), Cylas formicarius (Coleoptera: Brentidae). First, we found the most active mate search period of male SPW within 24 h. Then, we measured whether the duration of TI of virgin male and female were affected during the mate search. In the end, the Y-tube olfactometer was used to compare the duration of mate search and the proportion of orientation towards the females in two artificial selection groups of the male SPW with longer and shorter duration of TI. Our study confirmed that male mate searching increase after 3 h at night, and up to 73% at midnight, TI was affected by mate search in male, because the duration of TI of the male during mate search (Mean ± SE = 214.53 ± 22.74 s) was significantly shorter duration than the control (679.64 ± 69.77 s). However, mate search did not affect the strength of TI in the females tested. This study determined that mate search was affected by TI due to males from the group with shorter duration of TI who had 28% higher proportion of orientation towards the females than the males with longer duration of TI. Investment trade-off between TI and mate search was confirmed in the males of the SPW.