Visiting Plants of Mamestra brassicae (Lepidoptera: Noctuidae) Inferred From Identification of Adhering Pollen Grains

Morphological and DNA analysis of pollen grains on butterfly individuals reveal their flower visitation history

Many butterfly species are conspicuous flower visitors. However, understanding their flower visitation patterns in natural habitats remains challenging due to the difficulty of tracking individual butterflies. Therefore, we aimed at establishing a protocol to solve the problem using the Common five-ring butterfly, Ypthima argus (Nymphalidae: Satyrinae). Focusing on the pollen grains attached the butterfly's body surface, we examined validities of two pollen analyses based on pollen morphology and DNA markers (ITS1 and ITS2), in addition to the classical route census method. We captured thirty-nine butterflies from mid-April to early July and collected pollen grains from each individual. Morphological and DNA analyses of collected pollens identified eighteen and thirty-four taxa of insect pollinated plants respectively, including woody plants such as Castanopsis. The DNA analysis detected as many as thirteen plant taxa from a single butterfly, indicating its high sensitivity for detecting flower visitation. We detected more plant taxa in May when many individuals were flying. This is assumingly related to the post emergence days of the butterflies with more foraging experience. We also found that fluctuations of pollen grain numbers of Leucanthemum vulgare and Erigeron philadelphicus on individual butterflies depend on their flowering periods overlapping partly. Consequently, we conclude that pollen morphology and DNA barcoding analysis, and field observations are mutually complementary techniques, providing an integrated pollen analysis method to study the pollination ecology of butterflies.

Potential Regional Pollination Services of Spodoptera litura (Lepidoptera: Noctuidae) Migrants as Evidenced by the Identification of Attached Pollen

Many species of noctuid moths exhibit long-distance migratory behavior and have an important pollination service function in terrestrial ecosystems. Spodoptera litura (Fabricius) is a globally distributed insect; however, its role in pollination remains underexplored. In this study, the feeding preferences and inter regional pollination of S. litura adults were explored. We conducted pollen analysis on 1253 S. litura migrants captured from 2018 to 2021 on Beihuangcheng Island in the Bohai Strait of China, which is located in the East Asian insect migration path. The results show that an average of 51.1% of S. litura migrants carry plant pollen each year, and the carrying rate shows fluctuations based on sex, year, and season. By combining morphological identification and DNA barcoding, pollen species were identified from 40 species of plants, representing 21 families and 26 genera, mainly from angiosperms of Dicotyledoneae, with Asteraceae, Apocynaceae, and Amaranthaceae being the dominant taxa. The geographical distribution range of Chrysanthemum zawadskii and Adenophora trachelioides and a migration trajectory simulation analysis indicate that S. litura predominantly migrate from Liaoning Province in Northeast China to North China over the Bohai Sea in autumn. These findings indicate the potential pollination activities of S. litura in North China and Northeast China, enriching our understanding of the interaction between S. litura and the plants it pollinates.

Virus-host coevolutionary analyses of an Alphabaculovirus with a wide host range

Baculoviruses are highly host specific, and their host range is usually restricted to a single or a few closely related insect species, except for few virus species, e.g. Alphabaculovirus aucalifonicae and Alphabaculovirus mabrassicae. In this study, two new alphabaculovirus isolates were isolated from the larvae of Mamestra brassicae and Mythimna separata, which were named as Mamestra brassicae multiple nucleopolyhedrovirus isolate QD (MbMNPV-QD) and Mythimna separata multiple nucleopolyhedrovirus isolate Hb (MyseMNPV-Hb), respectively. The Kimura two-parameter values based on the concatenated 38 core genes of baculovirus revealed that MbMNPV (isolates QD/CHb1/K1/CTa), MyseMNPV-Hb, Helicoverpa armigera multiple nucleopolyhedrovirus (HearMNPV) and Mamestra configurata nucleopolyhedrovirus B (MacoNPV-B) were different isolates of a same virus species. A phylogenetic tree of baculoviruses and nudiviruses constructed from their 20 homologous gene sequences, and that of their isolated hosts constructed from 13 protein-coding genes of the insect mitochondrial genomes, were used to analyse the coevolution of baculoviruses with their isolated hosts. The results showed that M. brassicae was the most likely ancestral host of these virus isolates, included MbMNPV isolates, MyseMNPV-Hb, HearMNPV, and MacoNPV-B. Therefore, we concluded that these virus isolates belong to the existing virus species - Alphabaculovirus mabrassicae with M. brassicae as their ancestral host.

Pollen Molecular Identification from a Long-Distance Migratory Insect, Spodoptera exigua, as Evidenced for Its Regional Pollination in Eastern Asia

Understanding plant-insect interactions requires the uncovering of the host plant use of insect herbivores, but such information is scarce for most taxa, including nocturnal moth species, despite their vital role as herbivores and pollinators. In this study, we determined the plant species visited by an important moth species, Spodoptera exigua, by analyzing attached pollen on migratory individuals in Northeast China. Pollen grains were dislodged from 2334 S. exigua long-distance migrants captured between 2019 and 2021 on a small island in the center of the Bohai Strait, which serves as a seasonal migration pathway for this pest species, and 16.1% of the tested moths exhibited pollen contamination, primarily on the proboscis. Subsequently, 33 taxa from at least 23 plant families and 29 genera were identified using a combination of DNA barcoding and pollen morphology, primarily from the Angiosperm, Dicotyledoneae. Moreover, the sex, inter-annual, and seasonal differences in pollen adherence ratio and pollen taxa were revealed. Notably, compared to previously reported pollen types found on several other nocturnal moths, we found that almost all of the above 33 pollen taxa can be found in multiple nocturnal moth species, providing another important example of conspecific attraction. Additionally, we also discussed the indicative significance of the pollen present on the bodies of migratory individuals for determining their migratory route. Overall, by delineating the adult feeding and pollination behavior of S. exigua, we advanced our understanding of the interactions of the moths with their host plants, and its migration pattern, as well as facilitated the design of (area-wide) management strategies to preserve and optimize ecosystem services that they provide.

Windborne migration amplifies insect-mediated pollination services

Worldwide, hoverflies (Syrphidae: Diptera) provide crucial ecosystem services such as pollination and biological pest control. Although many hoverfly species exhibit migratory behavior, the spatiotemporal facets of these movement dynamics, and their ecosystem services implications are poorly understood. In this study, we use long-term (16-year) trapping records, trajectory analysis, and intrinsic (i.e., isotope, genetic, pollen) markers to describe migration patterns of the hoverfly Episyrphus balteatus in northern China. Our work reveals how E. balteatus migrate northward during spring–summer and exhibits return (long-range) migration during autumn. The extensive genetic mixing and high genetic diversity of E. balteatus populations underscore its adaptive capacity to environmental disturbances, for example, climate change. Pollen markers and molecular gut analysis further illuminate how E. balteatus visits min. 1012 flowering plant species (39 orders) over space and time. By thus delineating E. balteatus transregional movements and pollination networks, we advance our understanding of its migration ecology and facilitate the design of targeted strategies to conserve and enhance its ecosystem services.