The Ideal Sex Ratio Of Population And The Main Factor On Sex Ratio In Loxostege Sticticalis(Lepidoptera:Pyralidae)

Loxostege sticticalis L.is a major agricultural migratory pest in the world.Previous studies have shown that the large periodic occurrence of L.sticticalis is not only affected by environmental factors,also may be inherently restricted by the population’s own sex ratio.In this study,L.sticticalis was used as the research object,and indoor insect behavioral research methods were used to systematically study the ideal ratio of the L.sticticalis population in the absence of survival pressure.Based on this,the effects of larval density,parasitic natural enemies,and phototaxis on the sex ratio of L.sticticalis at different developmental stages were further explored.In order to predict the L.sticticalis population dynamics from the perspective of sex ratio,provides an important theoretical basis for the population forecasting and monitoring and early warning technology service,and the specific results are as follows:1.It was cleared that the maximum number of male mating times and the maximum number of offspring was 10 and 1230,the average number of mating times was 4.95±0.49,and the average number of offspring was 461.05±79.05.The maximum number of female mating times and the maximum number of offspring was 3 and 368,the average number of mating times was 1.70±0.15,and the average number of offspring was 154.96±22.57.It was shown that in the absence of survival pressure,the ideal ratio of female to male of L.sticticalis population was 2.9:1,under which the population can obtain the maximum growth rate.when female:male ratio was 3:1,2:1,1:1,1:2,1:3,namely the sex ratio was greater than or equal to 1:1,there was no significant difference between the average number of adult offspring.When the sex ratio dropped to 1:2,the average number of adult offspring was significantly lower than the sex ratio was 2:1.When the sex ratio dropped to1:3,the number of offspring was also significantly lower than the sex ratio was 1:2.It was showed that when the sex ratio was less than 3,the main limiting factor for the increase in the number of offspring of the population was the number of females.The higher the female ratio,the faster the population grow.The number of male mating times gradually decreased as the sex ratio decreased,there was a significant difference between the sex range from 3:1~1:1.When the sex ratio dropped to 1:2 and 1:3,there was no significant difference between the two sex ratios,but male mating times were significantly lower than the rest of the sex ratio.The number of female mating times increased with increasing sex ratio,and there was no significant difference between 3:1 and 2:1.Sex ratio has no significant effect on the longevity of female and male.2.With the feeding density of(1,5,10,20,30,40)larval/jar,as the larval density increased,the adult sex ratio of emerged L.sticticalis showed a trend of increasing and then decreasing.When the density was 10 larval/jar,the ratio of male to female was the largest,1.38±0.15.When the density was 1 larval/jar and 20 larval/jar,the ratio of male to female was closed to 1:1.And when the density was 30 larval/jar,the ratio of male tofemale was the smallest,0.80±0.08.The results showed that in the range of 1~20 larval/jar density,the proportion of females in the population was higher than 1:1,and in the range of 20~40 larval/jar density,the number of males was higher than 1:1.It was showed that the population can self-regulated by changing the sex ratio in the process of population growth.3.Exorista civilis has sex preference when parasitizing L.sticticalis larvae of different densities,and it has a additive effect on the effect of population density on sex ratio.That was,under low density(5 larval/jar),the female: male ratio was greater than 1,E.civilis prefers parasitic male larvae,further increasing the female: male ratio.Under high density(30 larval/jar),L.sticticalis female:male ratio was less than 1,E.civilis prefers parasitic female larvae,further reducing female to male ratio.The gender selection characteristics of E.civilis on L.sticticalis indicate that both the population density and E.civilis can regulate the population growth through the sex ratio,and reduce the number of females when the population was high,thereby inhibiting the growth of the population.In lower cases,population growth was promoted by reducing the number of males.4.There was a significant gender difference in the phototaxis between females and males.Female mainly flutter the lights in the early middle night and male flutter the lights in the later middle night,which was consistent with the autonomous flight rhythms of the females and males,but the total trend of phototaxis of females and males has no significant difference in response rates.Age has a significant effect on the phototaxis of adult males and females.9 to 13 days old females had significantly decreased phototaxis ability than males of the same age,indicated that age may affect the sex ratio of adults L.sticticalis under black light.Different breeding temperatures(16,22,28,34,40)℃ in the adult stage affected the flight ability and autonomous flight ability of females and males to a certain extent,but there was no significant differences in phototaxis between females and males.