Study On The Migratory Biology Of Helicoverpa Armigera(lepidoptera: Noctuidae)across The Bohai Strait

As an adaptive strategy of insects to pursue the seasonally changing natural resources,migration is an important factor leading to the regional outbreak of pests and sudden epidemic of plant diseases,and bringing serious challenges to agricultural production.Helicoverpa armigera(Lepidoptera: Noctuidae)is an important agricultural pest in the world,polyphagy,strong fecundity and facultative migration contribute to its wide distribution.Bohai Strait is an important passage of insect migration,it lies in the adjoint area between Northern China and Northeast China,thus,clarifying the biological characteristics of H.armigera across Bohai Strait is beneficial to the agricultural development in these areas.By using searchlight trap,ovarian dissertation,flight mill,scanning electronic photograph,PCR technique,micro topical and vial test,we studied their population dynamics,morphology,physiology,nectar plants and relative insecticide resistance level of migrative H.armigera across Bohai Strait,the main findings are listed as follows.The population dynamics were surveyed by conducting searchlight trap during migratory periods in 2017-2018,results showed that there are interannual and seasonal variances in population dynamic.The biomass in 2017 was 7.35 times higher than that in 2018,and it had an order of summer > fall > spring in the two years;With the female taking predominance in northward population and the male being majority in southward population,seasonal variations occur in sex ratio,as well.Ovarian dissection results demonstrated that the ovarian development level and mating frequencies declined as season progressed.The morphological parameters of northward and southward migrants were measured and compared during 2017-2018,results showed that body mass and body length of northward migrants were significantly heavier and longer than that of southward ones,and flight and reproductive experiments were enhanced in northward migrants in comparation to the southward cohorts.Identification of pollens from proboscis of 2015,2017 and 2018 migrants revealed that seasonal variation existed in pollen carrying ratio,with the northward migrants having the highest ratio and the mixed cohorts occupying the lowest ratio,Othenera L.was the most frequent plant in both northward and mixed migrants,Compositae was the most frequent in southward adults.By using 10% honey solution as nectar mimics to determine effects of nectar forage on the fitness of H.armigera migrants,we found that nectar feeding improved both flight and reproductive behaviors of migrants.Meanwhile,the improvement gradient varied seasonally.By conducting vial and micro-topical test,we monitored the relative resistance level of adult migrants and 3 instar larvae of their F1 generation to cyhalothrin,phoxim,indoxacarb and found that seasonal variation emerged in them.The highest resistance level occurred in larvae from early July,and resistance level declined since then,leading to a conclusion that migration diluted resistant genes;meanwhile,the lowest resistance level occurred in adults from 18 September.Furthermore,the resistance level of adults was not always positively related to that of larvae.By measuring population dynamics,morphology and fitness,host plants and insecticide resistance level of H.armigera,we illustrated the temporal variations in biological traits of H.armigera cross the Bohai Sea,which would provide valuable information for accurate forecasting and IPM of H.armigera.