| Abstract: | The presence of adequate nectar sources along the migratory pathway is a prerequisite for moths of oriental armyworm, Mythimna separata, to reach target habitats and lay eggs. Identification of plant species and assessment of their suitability as wild nectar sources along the summer migration pathway of adult M. separata are critical steps in making effective forecasts of second- and third-generation armyworm outbreaks in North China. We explored five aspects of moth-nectar source relationships: (1) Field investigations in 2014 and 2015 showed that the florescence of chaste tree, Vitex negundo var. heterophylla, a primary nectar plant in apiculture, coincided with the summer migration of oriental armyworm moths. The flowers of chaste tree opened day and night and M. separata moths were found actively flying around and resting on tree. (2) Identification of moth-borne pollen by scanning electronic microscopy (SEM) micrographs in 2015 and 2016 revealed that 15.4% of 369 moths trapped by blacklight traps, 17.1% of 557 moths captured by vertical-pointing searchlight traps and 24.4% of 311 moths caught by pheromone traps were found with pollen attached to their proboscis. A total of 228 pollen-carrying individuals out of 1 237 armyworm moths were captured by the three types of traps. The three highest percentages of pollen-bearing armyworm moths were carrying pollen of Toona sp. (59.65%), Ligustrum sp. (27.19%) and Syringa sp. (4.39%). In total, 14 types of pollen were detected where three were identified to species, 10 to genus and one as an unknown species. (3) Analysis of geographical distribution, flowering periods and relative abundances of candidate nectar plants suggested that Chinese toon, Toona sinensis, and privet, Ligustrum lucidum, were two important nectar plant species. (4) Analysis on relationship between pollen and ovarian development showed that 14, 15 and 10 females carrying pollen of T. sinensis had ovaries at developmental stages I, II and III, respectively. Many T. sinensis pollen grains were present on the proboscises of female moths. (5) Comparison of trap effectiveness between blacklight and vertical-pointing searchlight traps indicated blacklight traps caught the highest proportion (35.2%) of female in ovarian stage V, whereas vertical-pointing searchlight traps caught the highest proportion (43.5%) of female in ovarian stage I with additional proportions of decreasing percentages for stages II, III and IV. Integrated analysis on these five aspects suggests that T. sinensis is an important, suitable summer nectar source that potentially influences migration and reproduction of M. separata moths and thus contributes to outbreaks of this pest. The vertical-pointing searchlight trap was the most effective tool for monitoring the migratory flight of adult M. separata Privet, Ligustrum lucidum, and clove, Syringa sp., are possible suitable summer nectar plants that need further study to elucidate their importance. The reason why field investigation results on chaste tree differed from the results of moth-borne pollen analyses was discussed. |
