| Interactions between crop-feeding herbivores(H)and natural enemy insects(NE)are of crucial significance for ecosystem stability and prosperity.To adapt to seasonal variations in natural environments,numerous insects take long-distance,large-scale migrations in high altitude,leading to abrupt outbreaks of crop pests and diseases.Large number of migratory H and NE are linked into aerial interaction networks by predation and parasitism.Passed investigations on H—NE interactions were mainly focused on relatively fixed terrestrial or aquatic ecosystems,while detailed study on interactions between ongoing long-distance migrating species in high-altitude area is lacking.Bohai Bay is an important part of East Asia migration arena,numerous insects migrate through this corridor each year.Helicoverpa armigera(Lepidoptera: Noctuidae)is a dominated pest in Bohai Bay,and lacewings composed of Chrysopa pallens,Chrysoperla sinica and Chrysopa phyllochroma frequently occurred synchronously with H.armigera in this area,thus interpreting synchronous migration behaviors between cotton bollworms and lacewings facilitating improvement of food security.By adopting searchlight trap,stable isotope,trajectory analysis and pesticide bioassays,we investigated synchronous migration behaviors between cotton bollworms and lacewings from three aspects(spatio-temporal eco-niche,trophic level and insecticide resistance)systemically,the main results are summarized as follow:1.Coordinated migration between H and NE was pervasive in the East Asia,as total amount of 80 H from 5 orders 19 families and 18 NE from 5 orders 8 families jointly participated into migration.Chrysopidae and Ichneumonidae were most tightly related with the notorious Noctuid pests;annual migration periods of H and NE lasted for 209.3 days in average covering three seasons(spring,summer and fall)a year,as the spring arrival date of H was 14.3 days earlier than that of NE,and the migration ending time of H was 4.0 days longer than that of NE,the overall trend displayed that NE took into migration following the footprints of H.The migration food-web networks contained 124 pairs of potentially trophic-linked species consisting of 26 H and 17 NE,and marked changes occurred in foodweb structure across the season,all the migratory lacewings could prey on cotton bollworms,and interaction richness and generality of the migratory food web in June—September were higher than those in other months.2.Spatio-temporal ecological niche of cotton bollworms overlapped with that of lacewings,and dominate species of lacewings were different in different seasons,as C.sinica was dominate in spring and summer,and C.phyllochroma was dominate in autumn.Annual migration cycle of cotton bollworms and lacewings occurred in Northern China and Northeast China,while spring populations mainly took northward flights,and autumn populations mainly took southward migrations.3.Carbon isotopes in wings of migratory cotton bollworms were positively related with that of lacewings,and similar seasonal variations existed in the larval host plants of migratory cotton bollworms and lacewings,as spring populations were mainly from C3 plants,and the proportion of them from C4 plants was gradually increased as the season progressed.There are 10 nectar plants from similar families(genera)between C.sinica and H.armigera,and unlike bollworms like Othenera L.,lacewings were addicted to Acacia.Pollen adherence rate C.sinica in summer was higher than that in autumn,and female migrants revealed significantly higher adherence rate than males.4.Migratory C.pallens are extremely sensitive to lambda-cyhalothrin and phoxim,and the lethal concentration of them to C.pallens is much lower than that to H.armigera.Seasonal variations occurred in resistance level of H.armigera to chemical pesticides and Bt toxin Cry1 Ac,with different resistance trends to different pesticides.Resistance dilution appeared in migratory bollworms,as the summer populations has the highest resistance level to lambda-cyhalothrin;resistance level of bollworm to phoxim and emamectin benzoate showed seasonally upward trend,while resistance level of bollworm to indoxacarb,methomyl and chlorantraniliprole showed reverse trend.The resistance was 3 to 10.33 times to Cry1 Ac,and mutation frequency of resistant individuals was 7.5%—20%.Based on the analysis of the population dynamics and occurrence regularity of migratory H and NE in the Bohai Bay area,we revealed the ecological phenomenon of the coordinated migration between H and NE;by measuring spatio-temporal ecological niche,trophic relationships and insecticide resistance,our data provided a theoretical basis for clarifying ecological effects of migratory interactions between cotton bollworms and lacewings,which would benefit the implementation of green prevention and control. |
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