G-Protein Coupled Receptor Gpr-1 Is Important for the Growth and Nutritional Metabolism of an Invasive Bark Beetle Symbiont Fungi Leptographium procerum.

Leptographium procerum has been demonstrated to play important roles in the invasive success of red turpentine beetle (RTB), one of the most destructive invasive pests in China. Our previous studies found that bacterial volatile ammonia plays an important role in the maintenance of the RTB-L. procerum invasive complex. In this study, we found a GPCR gene Gpr-1 that was a response to ammonia but not involved in the ammonia-induced carbohydrate metabolism. Deletion of Gpr-1 significantly inhibited the growth and pathogenicity but thickened the cell wall of L. procerum, resulting in more resistance to cell wall-perturbing agents. Further analyses suggested that Gpr-1 deletion caused growth defects that might be due to the dysregulation of the amino acid and lipid metabolisms. The thicker cell wall in the ΔGpr-1 mutant was induced through the cell wall remodeling process. Our results indicated that Gpr-1 is essential for the growth of L. procerum by regulating the nutritional metabolism, which can be further explored for potential applications in the management of RTB.

Symbiotic microbes aid host adaptation by metabolizing a deterrent host pine carbohydrate d-pinitol in a beetle-fungus invasive complex.

The red turpentine beetle (RTB) is one of the most destructive invasive pests in China and solely consumes pine phloem containing high amounts of d-pinitol. Previous studies reported that d-pinitol exhibits deterrent effects on insects. However, it remains unknown how insects overcome d-pinitol during their host plant adaptation. We found that d-pinitol had an antagonistic effect on RTB, which mainly relied on gallery microbes to degrade d-pinitol to enhance host adaptation with mutualistic Leptographium procerum and two symbiotic bacteria, Erwinia and Serratia, responsible for this degradation. Genomic, transcriptomic, and functional investigations revealed that all three microbes can metabolize d-pinitol via different branches of the inositol pathway. Our results collectively highlight the contributions of symbiotic microbes in RTB's adaptation to living on pine, thereby facilitating outbreaks of RTB in China. These findings further enrich our knowledge of symbiotic invasions and contribute to the further understanding of plant-insect interactions.

Comparison between sustained effects of spray and injection thiamethoxam on apple aphids and non-target insects in apple orchard.

Spray application is considered to be the most common method of insecticide use in apple orchard, while trunk injection has often be used in labor-intensive areas. Here, a comparison of both methods in aphid control efficiency and non-target effects was conducted. We evaluated the effects of thiamethoxam by either spray or injection on apple aphid Aphis citricola, and examined the temporal dynamic of thiamethoxam in leaves by using residue analysis. Results showed that thiamethoxam had a remarkable suppression effect on Aphis citricola, and both application methods had obvious control efficiency with the highest value above 90%. The control effect of spray method on Aphis citricola reached the maximum at 7 days after application, while that of injection method reached the maximum at 14 days after application. Moreover, the control effect of injection after 14 days and that of spray after 7 days were not significant, suggesting the spray method had a higher quick-acting effect than the injection method, and the two methods had a similar persistence effect. The population dynamics of non-target insects (ladybugs, parasitoid wasps and predatory bugs) showed basically the same as that of blank controlled. The control effect evaluation of thiamethoxam on Aphis citricola suggest that injection treatment was more effective in protecting natural enemies than spray treatment, and thiamethoxam didn't interfere with natural enemies to control Aphis citricola with both two application methods.

Dietary risk evaluation of tetraconazole and bifenazate residues in fresh strawberry from protected field in North China.

Residues and dietary risk assessment of tetraconazole and bifenazate were investigated in strawberry under greenhouse conditions using high performance liquid chromatography (HPLC-DAD) after QuEChERs extraction in Beijing of China. The effects of different processing factors on the two pesticides were studied. The recoveries of tetraconazole and bifenazate were 87.0% and 89.1%, respectively. The dissipation curves of tetraconazole and bifenazate were in accordance with the first-order kinetic equation and the half-life were 5.92 d and 5.58 d, respectively. When the pre-harvest interval (PHI) was 3 d, the risk quotient (RQs) of both pesticides was less than 100%. Although soaking was a poor way to remove the two pesticides and heating at high temperatures increases the concentration of both pesticides, the residues of two pesticides can be effectively removed by washing after soaking. The results of dietary intake assessment indicated that potential dietary risk caused by tetraconazole and bifenazate in strawberry were acceptable for Chinese consumers.