Effects of ejaculate size on remating, attractiveness and oviposition in females of the sweetpotato weevil, Cylas formicarius

Authors: HIROYOSHI, SATOSHI - Okinawa Prefectural Institute; TAKAYUKI, MITSUNAGA - National Agriculture And Food Research Organization (NARO), Agricultrual Research Center; KOHAMA, TSUGUO - Okinawa Prefectural Institute; Reddy, Gadi V.P.

Submitted to: Entomologia Experimentalis et Applicata
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/6/2022
Publication Date: 1/19/2023
Citation: Hiroyoshi, S., Takayuki, M., Kohama, T., Reddy, G.V. 2023. Effects of ejaculate size on remating, attractiveness and oviposition in females of the sweetpotato weevil, Cylas formicarius. Entomologia Experimentalis et Applicata. 00:1–9. https://doi.org/10.1111/eea.13275.
DOI: https://doi.org/10.1111/eea.13275

Interpretive Summary: The sweetpotato weevil is an important pest of sweet potato in tropical and subtropical areas. In insects, males of many orders mate multiple times in their life. Depending on the species, males can even mate multiple times in a single day. In species with males that mate frequently, management of sperm levels by males can be via spermiogenesis, sperm storage or ejaculation.The present investigate the effects of ejaculate size on various aspects of female reproduction such as remating, attractiveness, and oviposition in the sweetpotato weevil. The results of this study showed that females that mated with young virgin males remated earlier than those that mated with older virgin males. The six-day fecundity did not differ between females that attracted males and those that did not. Given that the number of sperm in the spermathecae of females that had attracted males was smaller than that in females that did not attract males, we hypothesize that less ejaculate might enhance a female’s attractiveness to males. In conclusion, females of this weevil that had received small ejaculates were likely to be attractive to males, resulting in female remating, but cessation of oviposition is not due to sperm depletion alone, but rather is likely a response to a decrease in the level of seminal fluids.

Technical Abstract: In many insect species, female remating is triggered by the reduction in male ejaculates stored by female, including sperm and/or seminal fluids transferred during mating. Although females of the sweetpotato weevil, Cylas formicarius (Fabricius) are not monogamous, they are slow to remate. We investigated what factors determine female remating in this weevil. In an earlier study, we showed that a young (10-day-old) male that mated multiple times transferred a smaller ejaculate to females, whereas an older (30- or 50-day-old) male that mated just once had a large ejaculate. The results of this study showed that females that mated with young virgin males remated earlier than those that mated with older virgin males. The six day fecundity did not differ between females that attracted males and those that did not. Given that the number of sperm in the spermathecae of females that had attracted males was smaller than that in females that did not attract males, we hypothesize that less ejaculate might enhance a female’s attractiveness to males. Interestingly, 20% of females that had a relatively large number (>1000) of sperm in the spermatheca stopped laying eggs in the last observation day, suggesting that sperm depletion alone did not suppress oviposition behavior. In conclusion, females of this weevil that had received small ejaculates were likely to be attractive to males, resulting in female remating, but cessation of oviposition is not due to sperm depletion alone, but rather is likely a response to a decrease in the level of seminal fluids.