Abstract: 【Aim】 The subsocial parasitoid wasp Sclerodermus guani exhibits typical parental care behavior that extends throughout its offspring development. This prolonged parental investment, while potentially reducing the parental future reproductive capacity, can effectively enhance the survival rate of the current offspring, thereby promoting population development. The trade-off between parental care and reproduction entails a strategic decision for the parasitoid wasp, balancing the production of more offspring against the care of a limited number of offspring. The plasticity in parental ovarian development serves as a crucial adaptive mechanism to ensure the reproductive benefits at the population level. This plasticity not only regulates the utilization rate of limited host resources by parents but also promotes the survival and development of their offspring. This study aims to clarify the dynamics of ovarian development in S. guani before, during and after parental care, so as to provide a scientific basis for elucidating the physiological mechanisms underpinning parental care and reproductive trade-offs in this species. 【Methods】 In the 2-day-old S. guani adult females parasitizing Monochamus alternatus hosts and engaged in host for oviposition (within 12 d post inoculation), we conducted regular dissections to assess various quantitative traits associated with ovarian development (ovarian length and width, ovarian index, basal egg length and width, and number of eggs) and abdominal changes (abdominal length and width, and abdominal index) of the female adults. We evaluated the degree of ovarian development and investigated the relationship between abdominal physogastry stages and ovarian development in female adults. Additionally, we compared and analyzed the dynamic changes of ovarian development of S. guani female adults under different physiological states during the parental caring process. 【Results】 The progression of ovarian development of S. guani was classified into five periods (five levels) based on ovarian coloration, yolk deposition status and egg maturity: transparent period (level Ⅰ), vitellogenesis period (level Ⅱ), egg maturation period (level Ⅲ), egg-laying period (level Ⅳ) and late egg-laying period (level Ⅴ). Corresponding to this process, a typical abdominal physogastry of female adults was observed, and could be divided into 5 stages: non-physogastric stage, early physogastric stage, physogastric stage, last physogastric stage and physogastry termination stage. Both abdominal and ovarian quantitative traits of female adults exhibited a pattern of increase followed by decrease, with the exception of basal egg length and width. Prior to parental care, the newly emerged female adults ［(virgin female without feeding, VF) and (mated females without feeding (MF)］ were devoid of eggs. However, following mating and feeding, ovarian development in female adults (mated females with feeding, MFF) became progressively evident, the ovarian length ［(2 871.31±80.17) μm］, ovarian width ［(405.91±29.14) μm］, ovarian index ［(1.19±0.09) mm²］, and the number of eggs ［mature eggs: (7.94±1.49) grains; immature eggs: (9.76±1.70) grains］ of the mated females in the early oviposition stage (MFEO) all reached maximum values. The ovarian length and width and ovarian index of females caring for eggs (FCE) were notably greater during the egg-caring stage compared to other caring developmental stages. Eggs were observed within the ovaries of females in various parental caring states, including FCE, females caring for early instar larvae (FCEIL), females caring for mature larvae (FCML), and females caring for late pupal cocoons (FCLPC), while females in other states did not exhibit egg-carrying behavior. A significant positive association was identified between the abdominal index and ovarian index of female adults throughout ovarian development. 【Conclusion】 The ovarian development in adult female S. guani is closely linked to its feeding and parental care behaviors. When provided with additional nutrients, the ovaries of the female parents initiate development. However, during the period of caring offspring of S. guani, the ovarian development in the parent females is suppressed, despite of their reproductive potential. This mechanism ensures that parental care is prioritized to optimize the survival and development of the offspring S. guani.

Key words: Sclerodermus guani, parental care, ovarian development, reproduction trade-off