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Intergenerational effects of the entomopathogen Beauveria bassiana on the mortality and parasitism of the ectoparasitoid Sclerodermus guani (Hymenoptera: Bethylidae)
WEI Yun, LI Li, ZHANG Meng-Meng, PAN Shu-Mei
2023, 66(10):
1385-1403.
doi:10.16380/j.kcxb.2023.10.012
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【Aim】 Based on the complex relationship of competition and parasitism between two parasitic natural enemies, Beauveria bassiana and Sclerodermus guani in natural microhabitats, the adaptive reproductive strategies of parasitoids under the stress of B. bassiana were investigated, and the lethal and parasitic effects of the parental parasitoid carrying B. bassiana on itself and its offspring were comprehensively evaluated. 【Methods】 After the female adults of the parent (F48 generation) of S. guani were treated with the spore suspension of B. bassiana at different concentrations (1×104 , 1×105 and 1×106 conidia/mL) by the immersion method, and put into the test tubes containing the host Monochamus alternatus larvae, the mortality, cumulative mortality and corrected mortality, pre-oviposition period, oviposition period, total fecundity (total number of eggs laid) and number of eggs laid per female of the adults of the parent (F48 generation), and the mean developmental duration, survival rates, body weight per female and proportion of males of the corresponding offspring (F49 and F50 generations) were tested, and the dose and time effects of B. bassiana on the female adults of F48 and F49 generations during the lethal process were also determined by using the time-dose-mortality model (TDM). 【Results】 The pathogen load of S. guani female adults of the parent (F48 generation) increased with increasing concentration of B. bassiana spore suspension, with the average initial pathogen load of about 0.91×104 , 1.73×104 and 1.95×104 conidia/female, respectively, under the concentrations of 1×104 , 1×105 and 1×106 conidia/mL. Subsequently, B. bassiana was passed from the female adults of the parent (F48 generation) to the offspring (F49 generation) of S. guani , with an average initial pathogen load of 0.78×104 , 1.40×104 and 1.51×104 conidia/female, respectively, under the concentrations of 1×104 , 1×105 and 1×106 conidia/mL. This phenomenon of carrying B. bassiana by S. guan i (F48 generation) not only affected the longevity and reproduction of the female adults of F48 and F49 generations of S. guani, but also affected the fitness of their corresponding offspring (F49 and F50 generations). Compared with the control (non-inoculation with B. bassiana ), the stress of different concentrations of B. bassiana spore suspension resulted in a series of significant changes in the performance of the female adults of the parent (F48 generation) and the corresponding offspring (F49 generation), including the mean pre-oviposition period was shortened (F48 : shortened by 1.03, 1.43 and 2.03 d, respectively; F49 : shorted by 0.30, 0.80 and 1.00 d, respectively), the mean oviposition period was extended (F48 : extended by 0.30, 1.00 and 1.30 d, respectively; F49 : extended by 0.43, 0.73 and 1.43 d, respectively), the total number of eggs laid increased (F48 : increased by 4.80, 17.16 and 10.33 grains, respectively; F49 : increased by 11.57, 25.04 and 9.14 grains), and the number of eggs laid per female decreased (F48 : decreased by 4.07, 7.06 and 15.98 grains, respectively; F49 : decreased by 5.30, 9.37 and 20.47 grains, respectively). Similarly, the fitness of the corresponding offspring (F49 and F50 generations) of S. guani showed the same change trend. Overall, due to the transmission of B. bassiana at different concentrations (1×104 , 1×105 and 1×106 conidia/mL) carried by the female adults of the parent (F48 generation) of S. guani, the developmental process of its offspring (F49 and F50 generations) was obviously accelerated. After B. bassiana carried by the parent female adults of S. guani (F48 generation) was passed to the offspring, the generation time of the F50 generation was shortened by 3.00, 3.00 and 4.00 d, respectively, the survival rate and emergence rate of the F50 generation were decreased by 16.21% and 19.40%, respectively, the body weight per female actually increased by 0.09 and 0.94 mg, respectively, and the proportion of male offspring significantly decreased by 1.95% and 0.22%, respectively, as compared to those in the control. The TDM model showed that after inoculation with a high concentration (1×106 conidia/mL) of B. bassiana spore suspension, the female adults of the parent (F48 generation) of S. guani reached 50.83% mortality at 20 d after inoculation, while their corresponding offspring (F49 generation) reached 50.00% mortality at 18 d after emergence. The LT50 value of 1×106 conidia/mL of B. bassiana spore suspension against the parent female adults of S. guani was 22.72 d, and that against the female adults of the F49 generation was 24.352 d. Simultaneously, under other concentrations (1×104 and 1×105 conidia/mL) of B. bassiana spore suspension, the mortality of the female adults of F48 and F49 generations was less than 40.00%. 【Conclusion】 In response to B. bassiana stress, the parent female adults of S. guani not only reduce their fertility, but also indirectly affect the survival and development of their offspring. The concentrations of B. bassiana carried by the parent female adults of S. guani have a direct effect on the cumulative mortality of themselves and the female adults of the offspring, which increase with the increase in the concentration of B. bassiana spore suspension and test time. The dose and time effects of B. bassiana on the lethal process of S. guani show a significant interactive relationship.
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