Effects of stress by the natural enemy Whitmania pigra on population characteristics of Pomacea canaliculata Lamarck with different sex ratios

【Objective】 The purpose of the study was to investigate the response of Pomacea canaliculata Lamarck population with different sex ratios under the stress of the natural enemy Whitmania pigra,to explore changes of population characteristics of P. canaliculata under the natural enemy stress,and to provide scientific basis for revealing the rapid invasion strategies of P. canaliculata under natural enemy stress as well as for preventing and controlling P. canaliculata damage through the regulation of its sex ratios in breeding period.【Method】 By using three repeated randomized block experiments,three P. canaliculata populations with different sex ratios(2:1,1:1,and 1:2 for males and females,respectively) were put to coexist with the natural enemy W. pigra in aquaria for 21 d,with no W. pigra put in aquaria as the control,and the survival,feeding,behavior and reproductive characteristics(egg-laying amount,hatching rate,incubation period,etc.) of the P. canaliculata were regularly surveyed.【Result】 The survival of P. canaliculata was inhibited by the presence of W. pigra,and the survival rate of P. canaliculata populations with different sex ratios decreased by more than 50.0%, but the average daily intake of P. canaliculata was unaffected. The survival rate and average daily intake of P. canaliculata populations with a female-biased sex ratio were higher than those with an equal number of males and females and those with a male-biased sex ratio,which were higher than those of the latter two by more than 20.0% and 40.0% respectively. Reduced feeding(58.0% decline) and increased closed operculum(194.0% increase) in behavior of P. canaliculata were emerged in response to predation by W. pigra,but the impact of sex ratios was not distinct in the behavior of P. canaliculata. The lower the proportion of female in P. canaliculata,the lesser the egg-laying amount of the population, and the more obvious the inhibition of natural enemy. The egg-laying amount for female-biased population of P. canaliculata was not reduced under natural enemy stress,but egg-laying amount for male-biased population of P. canaliculata slumped by nearly 90.0%. The hatching rate of P. canaliculata eggs was enhanced by 32.0% and the incubation period was shortened by 8.0% in the presence of W. pigra.【Conclusion】 The presence of W. pigra can inhibit the survival and reproduction of P. canaliculata,but female-biased sex ratio is beneficial for P. canaliculata population to cope with natural enemy stress.