Research On The Sex Ratio Self-Balancing Of Aphidphagous Ladybeetle Harmonia Axyridis

Harmonia axyridis,as a predatory natural enemy insect species applied widely in production practice,is different from other enemy insect groups.In some areas,it occurred on a large scale and successfully invaded nearly all kinds of agroforestry and grass ecosystems,competing with local insect enemy species for sources,which caused the species simplification of natural enemy community,therefore affected the stability of natural enemy control function.The explosive occurrence of H.axyridis,is speculated that on the aspects of individual survival ability,including the ability to prey and escape from natural enemies,as well as the special response mode under abiotic stress factors,and the intra species sexual relationship and population fecundity.In order to explore the cause of regional outbreak of H.axyridis,we firstly investigated the natural adult population of H.axyridis in the agroforestry ecosystem in black soil cropping area,and determined the elytral color composition and sex ratio of the population.In the laboratory,we constructed a pair of female and male individuals with different background colors,as well as the application of insecticide,and we measured the background color and gender composition of its offspring adult.Combining with the above parameters of natural population,we calculated the background color proportion and gender composition of "deduced population"(next generation).In addition,the artificial indoor populations were constructed with different male and female ratio,and the life table parameters were observed,such as spawning amount,hatching rate and so on.Results showed that:(1)In the agroforestry ecosystems without insecticide application,the female proportion of H.axyridis adults was 51±2.2%,the proportion of individuals with yellow elytra was 85±1.8%;among female individuals,the proportion of yellow background was 84%,which was significantly lower than that of male with yellow background(87%).Accordingly,the proportion of individuals with black background of all the individuals was 15%.For the “deduced population” in the control group(without insecticide application),the proportion of female adults of H.axyridis was similar with that of the parent generation(52%),and the proportion of individuals with yellow background was also 85%,which was consistent with that of parent generation;in the treatment of exposure to pesticide,the proportion of female adults increased to60%,and that of individuals with black background increased to 26%.In the artificial population with different sex ratio of(3:7),(5:5),(7:3),(9:1),the female proportion of the offspring were 59%,52%,51%,57%,respectively.(2)The artificial population with sex ratio of(5:5)had the largest number of eggs per female,which was 659±32.The number of eggs laid in the treatment group with sex ratio of(3:7),(7:3)and(9:1)was 353±27,461±20 and 502±53,respectively.In the population with 50% female individuals,the female had middle level life span with 86±6 d,while the sex ratio was(3:7),(7:3)and(9:1),longevity was 54±3 d,93±5 d,115±4 d,respectively.And the larval and pupal development duration of offspring was the shortest,which was 16.00±0.23 d,meanwhile that of treatment with sex ratio of(3:7),(7:3)and(9:1)was 16.73±0.35 d,17.06±0.27 d and 16.32 ±0.14 d,respectively.Besides,the comprehensive daily reproductive rate(similar with the intrinsic growth rate)of the female was 1.7 times that of other sex ratio treatments.Conclusion: H.axyridis survive in agroforestry ecosystem in black soil cropping area with a large number,which is partly due to the increase of female proportion to keep the high population proliferation ability when facing the selection of adversity factors.After the relief of the adversity,the proportion of females will return to about 50% after one generation reproduction,and the reproduction rate per female of 50% female population is much higher than that of other populations with different sex ratio.At this time,the population development potential is the largest.Besides,when faced with abiotic stress factors such as insecticides,the proportion of yellow elytral H.axyridis decreased,while that with black background increased.Therefore,the diversity of body color composition and sex ratio of H.axyridis can respond to environmental pressure sensitively,which can reflect the environmental quality(whether there are pesticides and other stress factors).So it could be used as a potential environmental indicator.