The Preliminary Study On The Effects Of Nectar Plants’ Volatile And Nectar Viscosity On Oriental Armyworm Moth Mythimna Separata

Oriental Armyworm (OAW) Mythimna separata (Walker) is a migratory insect pestwhich frequently caused damage to cereal crops. The presence of nectar sources along thepathway (HuNan Province, JiangXi Province, ZheJiang Province, JiangSu Province, HuBeiProvince, AnHui Province, HeNan Province.) of the migratory population is a prerequisitefor OAW moths to reach target habitats and lay eggs. The acreage of milk vetch instopover area instead of rape was closely related with OAW’s outbreak. Unprecedentedenlargement in the geographic distribution of milk vetch from Central China into SouthChina was the key factor resulting in frequent severe OAW outbreaks that occurred during1966-1977. The volatile of the nectar plants could affect OAW moth’s selection to thenectar, the viscosity of the nectar could affect OAW moth’s rate of sucking nectar. Studyingthe effect of the volatile and viscosity of the nectar on OAW would be helpful for seekingthe suitability mechanism of milk vetch instead of rape for OAW moth’s nectar sucking,explaining the fluctuation of OAW among the years. Field tests and the Y-type pipe testwere carried out to observe OAW moth’s preference to milk vetch or rape. Collecting anddetecting sugar content and nectar volume in Jiang Province vs Southern Henan Provincewere carried out to verify the hypothesis that the higher sugar content and more nectar perflower of rape vs milk vetch had spatiotemporal stability. We used the quantitative capillaryrelative viscosity measurement method to detect the relative viscosity of nectar in the field,designed simulated nectar to study the viscosity’s affection to OAW moth. The followingare main results:1. In XinYang, Southern Henan Province, OAW moth tended to stay on the caged rape plant instead of milk vetch. But in the Y-type pipe test, OAW moth preferred for the milkvetch’s plants and its flower. The test about the effect of volatile and color of the nectarplants on OAW moth preference showed that the petals color and volatile was not thefactors which resulted in milk vetch more suitability for OAW nectar sucking.2. In Wuyuan county, Jiangxi Province, the results showed that:(1) The nectar sugarcontent of rape were higher but not significantly than that of milk vetch in the morning;(2)The nectar sugar content of rape was significantly higher than that of milk vetch at noonand in the evening;(3) The nectar volume per flower of rape was10times larger than thatof milk vetch in the morning, at noon and in the evening. These results were similiar withWang’s report (2011) and indicated the stable comparative characteristics on nectar volumeper flower between rape and milk vetch.3. There were three kinds of capillary used in our test (0.5μL，1μL，5μL), we used the5μL capillary as tool for detecting relative viscosity (rising time of nectar reach half pipeheight) of nectar because of the relatively stable absorption and convenient observation.When we detected the milk vetch nectar, which average sugar content was32%, theaverage rising time was3.14s. When we detected the rape nectar, which average sugarcontent was52%, the average rising time was9.71s. According the relative viscosity data,we designed milk-vetch-simulated nectar and rape-simulated nectar by adding methylcellulose in15%sugar solution.4. OAW moth’s sucking amount to milk-vetch-simulated nectar (15%sugar content,0.20%methyl cellulose content)was0.43g per female per day,0.38g per male per on theaverage. Fecundity of OAW moth fed by milk-vetch-simulated nectar was282.97per dayon the average. OAW moth’s sucking amount to rape-simulated nectar (15%sugar content,0.29%methyl cellulose content) was0.36g per female per day,0.31g per male per day onthe average. Fecundity of OAW moth fed by rape-simulated nectar was245.25per day onthe average.