Plants produce reactive oxygen species (ROS) to defend pathogens.  To counteract this attack, certain pathogens express superoxide dismutases (SODs) to scavenge host-derived ROS.  However, the roles of SODs in Verticillium dahliae, an important vascular pathogen, are not clear.  Our previous study has shown that a putative extracellular SOD (VdSOD5) of V. dahliae is significantly induced by culturing in cotton tissues, suggesting that VdSOD5 may play an important role in host–pathogen interactions and virulence.  Here, we showed that VdSOD5 encoded a superoxide dismutase with a co-factor copper-binding site and a functional signal peptide that can conduct protein secretion in an invertase-mutated yeast strain.  The mutations in VdSOD5 (ΔVdSOD5) did not change the normal vegetative growth and conidial production but reduced the virulence of V. dahliae on susceptible host cotton.  Further studies showed that the transcription of VdSOD5 was significantly up-regulated during the early stage of infection, and the loss-of-function of VdSOD5 decreased culture filtrate and fungal tissue SOD activities of V. dahliae by 74 and 28%, respectively.  Compared to the wild-type strain Vd991, the ΔVdSOD5 showed the same sensitivity to the intracellular ROS generator menadione.  Furthermore, nitroblue tetrazolium (NBT) staining demonstrated that VdSOD5 functioned in the detoxification of superoxides generated by host roots during infection.  These results suggest that VdSOD5 of V. dahliae is an important virulence factor, secreted out of cells to combat host-derived ROS. 

Light traps are widely utilized to monitor and manage insect pest populations.  In late 2018, the fall armyworm (FAW), Spodoptera frugiperda, invaded China through Yunnan Province representing a huge threat to grain production.  To estimate the efficiency of light traps on FAW moths, we first identified the opsin genes from FAW by using the transcriptome.  Phylogenetic analysis indicated that the four opsins of FAW were clustered with those of other Noctuidae species.  The expressed levels of opsins in S. frugiperda were lower than in Helicoverpa armigera, suggesting a different phototactic response between the two species.  Then, we determined the phototactic behavior of FAW using H. armigera as a control, which is widely monitored and managed using light traps in China.  Our results indicated that the two moths species showed significantly different phototactic behavior and both female and male FAW displayed faster flight-to-light speed than H. armigera.  This may be due to a faster flight capacity in FAW compared to H. armigera.  However, the capture rate of both female and male of S. frugiperda was significantly lower than that of H. armigera, which was consistent with the expression levels of opsins.  These results support the positive phototaxis of S. frugiperda moths and suggest light traps could be used for monitoring and managing the pests, but with a lower efficiency than H. armigera.

The fall armyworm (FAW) Spodoptera frugiperda, which originated in the Americas, is advancing across China and threatening the nation’s maize crops.  Currently, one widely used tool for its control is genetically modified (GM) Bacillus thuringiensis (Bt) maize.  Sufficient content of Bt protein in appropriate plant parts is crucial for enhancing resistance against insect pests.  In this study, we conducted a systematic investigation of Cry1Ab levels in Chinese domestic GM maize DBN9936, which has recently obtained a biosafety certificate, and evaluated its efficacy against FAW.  Quantification of expression levels of Cry1Ab, via ELISA, indicated a spatio-temporal dynamic, with significant variation of mean Cry1Ab, ranging from 0.76 to 8.48 μg g^–1 FW with the Cry1Ab protein level ranked as: V6–V8 leaf>R1 leaf>R4 leaf>R1 silk>VT tassel>R4 kernel.  Among the nine locations, the Cry1Ab levels in DBN9936 of the Xinxiang, Langfang, and Harbin fields were significantly lower than those from Wuhan and Shenyang, and were slightly, but not significantly lower than those from the other four fields.  Furthermore, the artificial diet–Cry1Ab mixture and plant tissue feeding bioassays revealed that DBN9936 has high efficacy against FAW.  The insecticidal efficacy of different tissues against FAW larvae reached 34–100% with a descending order of lethality as follows: VT leaf>R4 leaf>R1 husk>R1 silk>VT tassel>R4 kernel.  Taken together, our results showed that Bt-Cry1Ab maize DBN9936 has potential as a promising strategy to manage FAW.

 

Fall armyworm has invaded China and colonized its populations in tropical and sub-tropical regions of South China since December 2018.  Chemical spray has been widely used to control the pest, which shall lead to resistance evolution.  In this research, we collected five populations of the pest from Yunnan, Hainan, Tibet, and Fujian of China, and tested their susceptibilities to pyrethroid, organophosphorus, oxadiazine, diamide, antibiotics and other types of insecticides (14 insecticides totally) in the laboratory.  Based on the susceptible baseline published from the previous studies, the resistance ratio was 615–1 068-fold to chlorpyrifos, 60–388-fold to spinosad, 26–317-fold to lambda-cyhalothrin, 13–29-fold to malathion, 9–33-fold to fenvalerate, 8–20-fold to deltamethrin, 3–8-fold to emamectin benzoate and 1–2-fold to chlorantraniliprole, respectively.  The median lethal concentration (LC₅₀) of other six insecticides without the susceptible baselines was 148.27–220.96 µg mL^–1 for beta-cypermethrin, 87.03–128.43 µg mL^–1 for chlorfenapyr, 16.35–99.67 µg mL^–1 for indoxacarb, 10.55–51.01 µg mL^–1 for phoxim, 7.08–8.78 µg mL^–1 for M-EBI (the mixed insecticide of emamectin benzoate and indoxcarb) and 1.49–4.64 µg mL^–1 for cyantraniliprole.  This study can be helpful for chemical control as well as for resistance monitoring and management of the pest in China.

 

Fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), has become an important pest in Chinese agricultural systems since its invasion on 11 December 2018.  After its establishment, FAW months in the year-round breeding region have become the main source population migrating to other areas in China.  Field investigations were conducted in tropical and subtropical regions to improve understanding of its year-round breeding area in China.  The results showed that FAW larval density was significantly correlated with the seasonal temperature of the location surveyed.  The FAW larvae maintained a high density in the tropical area and were frequently found in sites of the south subtropical region, but were absent from the north subtropical region and the northern part of the central subtropical region.  These results indicated that FAW can reproduce annually in the tropical and south subtropical regions of China, including Hainan, Taiwan and the southern area of Fujian, Guangdong, Guangxi, Guizhou, and Yunnan.  Hence, great effort should be made to monitor and control FAW in the year-round breeding region to suppress the population density of this area and to reduce migration of moths into northern parts of China.  This study clarifies the occurrence area of the pest in winter in China and provides much valuable information for its population forecasting and management.

Fall armyworm, Spodoptera frugiperda (J. E. Smith, 1797), a crop pest native to tropical and subtropical regions of America, has invaded and spread into most regions in China, posing a severe threat to China’s agriculture.  The cold hardiness directly determines its geographic distribution through adapting to winter temperatures of different regions.  Here, we measured supercooling points and lethal time (LT) at low temperatures of S. frugiperda.  The supercooling points for developmental stages in increasing order were: adults (–15.05°C)<pupae (–13.25°C)<prepupae (–10.50°C)<larvae (–9.03°C).  Among eggs and 1st to 4th instar larvae, the 99% lethal time (LT₉₉) was the highest for 4th instar larvae, with 99% of larvae dying after 18.59 d at 2°C, 58.72 d at 7°C, and 66.28 d at 13°C.  LT₉₉ was the lowest for eggs with LT₉₉ of 5.33 d at 2°C, 9.28 d at 7°C, and 12.97 d at 13°C.  This study provides an understanding of overwintering regions of S. frugiperda in China, which will be helpful for population forecasting and management.