The fall armyworm (FAW), Spodoptera frugiperda, is a destructive pest native to America and has recently become an invasive insect pest in China. Because of its rapid spread and great risks in China, understanding of FAW genetic background and pesticide resistance is urgent and essential to develop effective management strategies. Here, we assembled a chromosome-level genome of a male FAW (SFynMstLFR) and compared re-sequencing results of the populations from America, Africa, and China. Strain identification of 163 individuals collected from America, Africa and China showed that both C and R strains were found in the American populations, while only C strain was found in the Chinese and African populations. Moreover, population genomics analysis showed that populations from Africa and China have close relationship with significantly genetic differentiation from American populations. Taken together, FAWs invaded into China were most likely originated from Africa. Comparative genomics analysis displayed that the cytochrome p450 gene family is extremely expanded to 425 members in FAW, of which 283 genes are specific to FAW. Treatments of Chinese populations with twenty-three pesticides showed the variant patterns of transcriptome profiles, and several detoxification genes such as AOX, UGT and GST specially responded to the pesticides. These findings will be useful in developing effective strategies for management of FAW in China and other invaded areas.

Frankliniella occidentalis is a highly destructive and invasive agricultural pest that has developed resistance to a variety of insecticide classes. Different planting structures and insecticide use frequency can directly affect the resistance development of F. occidentalis. In this study, the susceptibility of three field strains of F. occidentalis, collected over one year (April to November) from three habitat conditions (facility agriculture area, FA; open field crop area, OF; agroforestry intersection area, AI), to spinetoram, spinosad, emamectin benzoate, chlorfenapyr, acetamiprid, and imidacloprid were monitored and compared. At the same time, the detoxification enzyme activity of F. occidentalis in different habitats was determined. The results showed that the susceptibility of the F. occidentalis population in FA was significantly lower than that of populations from OF and AI. Among them, the F. occidentalis population in FA had developed low levels of resistance to spinetoram (RR = 9.18-fold), emamectin benzoate (RR = 5.47-fold), chlorfenapyr (RR = 6.67-fold), and acetamiprid (RR = 7.49-fold), and had developed moderate level resistance to imidacloprid (RR = 11.67-fold), while still being relatively sensitive to spinosad. The population of F. occidentalis from OF had developed low level resistance to spinetoram (RR = 5.24-fold) but was still relatively sensitive to the other five insecticides. The resistance of F. occidentalis from AI to six insecticides was at relatively sensitive levels. The results of the enzyme activities of detoxification enzymes, including carboxylesterase (CarE), glutathione S-transferase (GST), acetylcholinesterase (AChE), and the cytochrome P450 enzyme system (CYP450), revealed that the activities of the FA population of F. occidentalis were significantly higher than those of the other two populations. The change of CarE activity in F. occidentalis was consistent with that of spinetoram resistance, indicating that CarE may be involved in the metabolic resistance of F. occidentalis to spinetoram. Among the three populations, the resistance and detoxification enzyme activities of F. occidentalis of the FA population to six insecticides were higher than those of the other two populations. Our findings, along with other strategies, are expected to help with the resistance management of F. occidentalis in different habitats.

The fall armyworm (FAW), Spodoptera frugiperda, is one of the most important invasive species and causes great damage to various host crops in China. In this study, the diversity and function of gut bacteria in the 5th instar larvae of FAW fed on maize, wheat, potato and tobacco leaves were analyzed through 16S rRNA sequencing. A total of 1324.25 ± 199.73, 1313.5 ± 74.87, 1873.00 ± 190.66 and 1435.25 ± 139.87 operational taxonomic units (OTUs) from the gut of FAW fed on these four different host plants were detected, respectively. Firmicutes, Proteobacteria and Bacteroidetes were the most abundant bacterial phyla. Beta diversity analysis showed that the gut bacterial community structure of larvae fed on different host plants was significantly differentiated. At the genus level, the abundance of Enterococcus in larvae fed on wheat was significantly lower than those fed on the other three host plants. Enterobacter and ZOR0006 were dominant in FAW fed on tobacco leaves, and in low abundance in larvae fed on wheat. Interestingly, when fed on Solanaceae (tobacco and potato) leaves which contained relative higher levels of toxic secondary metabolites than Gramineae (wheat and maize), the genera Enterococcus, Enterobacter and Acinetobacter were significantly enriched. The results indicated that gut bacteria were related to the detoxification and adaptation of toxic secondary metabolites of host plants in FAW. Further analysis showed that replication, repair and nucleotide metabolism functions were enriched in the gut bacteria of larvae fed on tobacco and potato. In conclusion, the gut bacterial diversity and community composition in FAW larvae fed on different host plants showed significant differences, and the insect is likely to regulate their gut bacteria for adaptation to different host plants.

The rhizospheric microbial community affects the population establishment of invasive plants in introduced areas, among which Bacillus has numerous functions in promoting plant growth. This study isolated and enriched the Bacillus community in the rhizospheric soil of the invasive plant Ageratina adenophora and the native accompanying plant Rabdosia amethystoides. The effects of these rhizospheric Bacillus communities on the growth and competition of A. adenophora and R. amethystoides were evaluated in pot experiments. The results showed that the number and diversity of Bacillus in the rhizospheric soil of A. adenophora were higher than those of R. amethystoides (A. adenophora: 122 strains in soil, 16 Bacillus taxa; R. amethystoides: 88 strains in soil, 9 Bacillus taxa). After Bacillus inoculation of A. adenophora in a pot experiment, Bacillus idriensis, Bacillus toyonensis and Bacillus cereus were accumulated in the rhizospheric of A. adenophora, which significantly increased the nitrate nitrogen (NO₃^–-N) content in the soil and the total carbon and nitrogen concentrations in A. adenophora in the mixed treatment. The selective accumulation of Bacillus enhanced the competitive advantage of A. adenophora over the native accompanying plant; the corrected index of relative competition intensity of A. adenophora-inoculated Bacillus reached double that of the uninoculated treatment, and the growth of native plants was greatly suppressed under mixed planting. Our study confirmed that invasion of A. adenophora can lead to the accumulation of specific Bacillus taxa in the rhizospheric soil, which in turn can increase the competitive advantage of A. adenophora.