The Asian citrus psyllid ( Diaphorina citri ) is a major pest of citrus trees as it transmits Candidatus Liberibacter asiaticus ( C Las). The composition of a host’s microbiota can affect the evolution and ecological distribution of the host. This study monitored the compositional shifts in the citrus psyllid microbiota through all the life stages (egg, nymph 1–5 stages, and adult) by next-generation sequencing (NGS) and quantitative real-time PCR. There were clear differences in both α- and β-diversity of microbiota through the psyllid life stages. Microbiota diversity was markedly higher in the nymph 2–5 stages than in the adult, egg, and nymph 1 stages. Proteobacteria were dominant in all the life stages of D. citri , representing >97.5% of the total bacterial community, and Candidatus Profftella armature was the dominant genus in all the life stages. Data from the qPCR analysis showed an exponential increase in the populations of three D. citri endosymbionts: Candidatus Profftella armature, Candidatus Carsonella ruddii, and Wolbachia . The gut bacterium Pantoea was present in all the life stages, but it was markedly higher in the nymph 2–5 stages. The microbiota composition substantially differed among the egg–nymph 1, nymphs 2–5, and adult stages. Therefore, we successfully characterized the microbiota dynamics and thus identified a microbiota shift during the life cycle of D. citri by 16S rRNA gene sequencing and quantitative PCR. Moreover, 16S rRNA gene sequencing suggested that D. citri acquired the ability to bear C Las in the nymph 1 stage. This study enhances our understanding of microbial establishment in the developing D. citri and provides a reference resource for the identification of potential biocontrol approaches against this pest.

The Asian citrus psyllid Diaphorina citri Kuwayama is a major pest in citrus production, transmitting Candidatus Liberibacter asiaticus. It has spread widely across eastern and southern China. Unfortunately, little is known about the genetic diversity and population structure of D. citri, making pest control difficult. In this study, nine specifically developed SSR markers and three known mitochondrial DNA were used for population genetics study of D. citri using 225 samples collected from all 7 distribution regions in China. Based on the SSR data, D. citri was found highly diverse with a mean observed heterozygosity of 0.50, and three subgroups were structured by host plant: (i) Shatangju, NF mandarin and Ponkan; (ii) Murraya paniculata and Lemon; (iii) Citrus unshiu, Bingtangcheng, Summer orange and Navel. No significant genetic differences were found with mtDNA data. We suggested the host-associated divergence is likely to have occurred very recently. A unimodal distribution of paired differences, the negative and significant Tajima’s D and Fu’s FS parameters among mtDNA suggested a recent demographic expansion. The extensive citrus cultivation and increased suitable living habitat was recommended as a key for this expansion event.

BACKGROUND Mycopesticides are important for integrated management of the Asian citrus psyllid, Diaphorina citri. However, there are few reports on the fermentation and formulation for mycopesticides with high virulence against D. citri. RESULTS From four different locations in South China, 12 fungal strains were isolated and classified into Beauveria bassiana (two isolates), Fusarium fujikuroi (five isolates), and Cordyceps javanica (five isolates) based on the phylogenetic analysis of ITS1‐5.8S rDNA‐ITS4 and morphology of colonies and conidia. Based on the highest initial virulence (86.52 ± 2.35%) and best growth characteristics, F‐HY002‐ACPHali was further optimized for biphasic fermentation (7.85 ± 2.62 × 109 g–1 dry substrate) with soybean meal + cottonseed flour (1:1) as the solid substrate and full light as the light/dark cycle. Furthermore, the oil‐based conidial formulation was optimized with sesame oil as an effective carrier, which significantly enhanced conidial shelf life up to 16 weeks at 26 °C and 4 °C, thermo‐stress (50 °C) and UV‐B stress resistance, and virulence against adults of D. citri with increased mortalities and decreased LT50 in comparison to that of unformulated conidia. CONCLUSION Our results not only provide a valuable native strain with high virulence against adults of D. citri, but also imply the soybean meal + cottonseed flour as valuable solid substrate, full‐light exposure as environmental stimuli for solid‐state fermentation, and the sesame oil as an effective carrier for the formulation of the C. javanica. These findings will facilitate the development of a potential mycopesticide for the biological control of Asian citrus psyllid.

The effects of five host plant species – tangerine, Citrus reticulata Blanco cv. Shatangju, C. reticulata cv. Ponkan, orange jasmine, Murraya paniculata (L.) Jack, lemon, Citrus limon (L.) Osbeck, and navel orange, Citrus sinensis (L.) Osbeck (all Rutaceae) – on the life‐table parameters and host preference of the citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), were evaluated under laboratory conditions. In the presence of the host plants tested, citrus psyllid showed higher preference for navel orange, followed by Shatangju and orange jasmine. Total nymph duration of D. citri was longest on lemon (14.1 days) and shortest on Shatangju (12.7 days). The survival rate (lx) of citrus psyllid on orange jasmine was significantly higher than on other tested host plants. The highest longevity of females was observed on lemon (47.6 days), whereas the shortest was on navel orange (40.5 days). The total number of eggs laid by females was not significantly different among host species. The net reproductive rate (R0) was significantly affected by host plants, being highest on Shatangju (162.1 females/female per generation) and lowest on navel orange (130.7). The intrinsic rates of natural increase (rm) was not significantly different among hosts, and ranged from 0.112 on lemon to 0.123 on orange jasmine. Cluster analysis of the life‐table parameters of D. citri on five host plant species indicated that Shatangju was the most suitable host to D. citri, followed by orange jasmine, and navel orange was the least suitable.

Diaphorina citri Kuwayama (Hemiptera: Liviidae) can cause severe damage to citrus plants, as it transmits Candidatus Liberibacter spp., a causative agent of Huanglongbing disease. Symbiotic bacteria play vital roles in the ecology and biology of herbivore hosts, thereby affecting host growth and adaptation. In our research, the effects of Rutaceous plants (i.e., Citrus reticulata cv. Shatangju, Citrus poonensis cv. Ponkan, Murraya paniculata (orange jasmine), Citrus limon (lemon), and Citrus sinensis (navel orange)) on the gut microbiota (GM) and microbial diversity of D. citri adults were investigated by 16S rRNA high-throughput sequencing. It was found that Proteobacteria dominated the GM communities. The gut microbe diversity was the highest in the ponkan-feeding population, and the lowest in the Shatangju-feeding population. The NMDS analysis revealed that there were obvious differences in the GM communities among the different hosts. PICRUSt function prediction indicated significant differences in host function, and those pathways were crucial for maintaining population reproduction, growth, development, and adaptation to environmental stress in D. citri. Our study sheds new light on the interactions between symbionts, herbivores, and host plants and expands our knowledge on host adaptation related to GM in D. citri.