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Scientia Silvae Sinicae ›› 2022, Vol. 58 ›› Issue (6): 161-168.doi: 10.11707/j.1001-7488.20220616

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Effects of Different Foundress Densities on Sex Ratio of the Offspring of Bethylid Wasps

Yanlong Tang1,Lina Wang1,Yanqin Wang1,Yanlong Zhang2,Xiaoyi Wang2,Ke Wei2,*   

  1. 1. Laboratory of Regional Characteristic for Conservation and Utilization of Plant Resource in Chishui River Basin College of Biology and Agriculture, Zunyi Normal University Zunyi 563002
    2. Key Laboratory of Forest Protection of National Forestry and Grassland Administration Ecology and Nature Conservation Institute, Chinese Academy of Forestry Beijing 100091
  • Received:2021-03-22 Online:2022-06-25 Published:2022-09-24
  • Contact: Ke Wei

Abstract:

Objective: Sex ratio adjustability is a widespread ecological phenomenon in parasitic wasps. A female-biased sex ratio has long been asserted as the evolutionary stable strategy for some gregarious parasitic wasps on account of the theory of local mate competition (LMC). This evolutionary stable sex ratio can only be equalized as the increasing of foundresses numbers. The bethylid wasps have been widely used as biocontrol agents for several cerambycid and buprestid larvae, and their sex ratio structures are the basis of biocontrol. This study aims to clarify the sex ratios of the bethylid wasps and to prove whether the LMC model was applicable to the prediction of their sex ratios under different foundress densities. Method: In this study, Sclerodermus guani, S. pupariae, and S. alternatusi were selected as the experimental objects. The changes of offspring sex ratio and the brood size per female of three bethylid wasps were analyzed when the foundress densities ranged from one to eight respectively. The measured sex ratio of these three parasitoids and their predicted sex ratio based on LMC model under different foundress densities were comparatively studied. Result: The results indicated that the sex ratio of these three parasitoids were highly female-biased. Brood size per foundress significantly reduced when the numbers of foundress increased from one to eight. The sex ratio of these bethylid parasitoids exhibited slightly increase with the increasing foundress densities and negatively related to the brood size per foundress. Meanwhile, the predicted sex ratios based on the LMC model of these bethylid parasitoids deviated significantly from their measured sex ratios. Conclusion: The extremely female-biased sex ratio is an evolutionary stable biological characteristic for the bethylid parasitoids. This female bias of the bethylid parasitoids cannot be equalized, even though it would become a slightly less biased, with increasing numbers of foundress. The LMC model cannot accurately reflect the fluctuations of bethylid sex ratio under different foundress densities.

Key words: sex ratio, local mate competition, parasitic wasp, biological control

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