Yuejin Wang

Transcriptional inhibition of the Catalase gene in phosphine-induced oxidative stress in Drosophila melanogaster.

Phosphine (PH3) is a toxic substance to pest insects and is therefore commonly used in pest control. The oxidative damage induced by PH3 is considered to be one of the primary mechanisms of its toxicity in pest insects; however, the precise mode of PH3 action in this process is still unclear. In this study, we evaluated the responses of several oxidative biomarkers and two of the main antioxidant enzymes, catalase (CAT) and superoxide dismutase (SOD), after fumigation treatment with PH3 in Drosophila melanogaster as a model system. The results showed that larvae exposed to sub-lethal levels of PH3 (0.028 mg/L) exhibited lower aerobic respiration rates and higher levels of hydrogen peroxide (H2O2) and lipid peroxidation (LPO). Furthermore, unlike SOD, the activity and expression of CAT and its encoding gene were downregulated by PH3 in a time- and dose-dependent manner. Finally, the responses of six potential transcription factors of PH3 were determined by real-time polymerase chain reaction to explore the regulation mechanism of DmCAT by PH3. There were no significant effects of PH3 on three nuclear factor-kappa B homologs (DORSAL, DIF, and RELISH) or two activator protein-1 genes (JUN and FOS), while dramatic inhibition of DNA replication-related element factor (DREF) expression was observed after fumigation with PH3, suggesting that PH3 could inhibit the expression of DmCAT via the DRE/DREF system. These results confirmed that PH3 induces oxidative stress and targets CAT by downregulating its encoding gene in Drosophila. Our results provide new insight into the signal transduction mechanism between PH3 and its target genes.

Toxicity of Phosphine Fumigation Against Bactrocera tau at Low Temperature

ABSTRACT Bactrocera tau (Walker) is one of the most harmful pests to fruits and vegetables. To counteract this pest, the development of phytosanitary treatment is required to comply with the pest regulation requirements of certain countries. This study investigated the toxicity of phosphine fumigation against B. tau under low temperature conditions. Different growth stages (eggs and instars) of B. tau were exposed to 1.07 mg/liter phosphine for 1–10 d at 5°C, and compared with unfumigated flies at 5°C. The results showed that tolerance to cold treatment alone or phosphine fumigation at low temperatures generally increased with the stage of insect development. However, eggs incubated for 12 h at 25°C represented the most tolerant growth stage to phosphine fumigation at 5°C. Furthermore, 8.56- to 2.18-d exposure periods were required to achieve 99% mortality with a range of phosphine concentrations from 0.46 to 3.81 mg/liter. C0.62 t = k expression was obtained from the LT99 values, indicating that the exposure time was more important than the phosphine concentration.

Differential Expression Profiles of Alternaria alternate Genes in Response to Carbonyl Sulfide Fumigation

Carbonyl sulfide (COS) is a new fumigant used in phytosanitary treatments. It was developed as a potential alternative to methyl bromide, which is being phased out because of its ozone-depletion properties. To understand the molecular and cellular mechanisms occurring in fungal pathogens in response to COS fumigation, we cloned 510 cDNA fragments of Alternaria alternata (Fr.) Keissler genes that are differentially expressed; these genes were cloned using suppression subtractive hybridization. Changes in the levels of transcripts of 79 fragments were confirmed by microarray analysis and qRT-PCR. Further homology search revealed that they are highly homologous to 41 genes of other fungi, which were related to general metabolism, growth and division, defense, cellular transport, and signal transduction. These results provide an overview of differential expression profiles of A. alternata genes following COS treatment and some new clues about the mechanism of COS fungitoxicity.

Effect of Low-Temperature Phosphine Fumigation on the Survival of Bactrocera correcta (Diptera: Tephritidae)

ABSTRACT This laboratory-based study examined the effects of low-temperature phosphine fumigation on the survival of the eggs and larvae of the guava fruit fly, Bactrocera correcta (Bezzi). Individual flies at different developmental stages, from 6-h-old eggs to third instars, were exposed to 0.92 mg/liter phosphine for 1–7 d at 5°C. We found that 12-h-old eggs and third instars were the most tolerant to phosphine. Increasing phosphine concentrations from 0.46 to 4.56 mg/liter increased mortality in these two stages. However, increased exposure times were required to achieve equal mortality rates in 12-h-old eggs and third instars when phosphine concentrations were ≥4.56 and ≥3.65 mg/liter, respectively. Cnt = k expression was obtained at 50, 90, and 99% mortality levels, and the toxicity index (n) ranged from 0.43 to 0.77 for the two stages. The synergistic effects of a controlled atmosphere (CA) with elevated CO2 levels were also investigated, and we found that a CO2 concentration between 10% and 15% under CA conditions was optimal for low-temperature phosphine fumigation.

Evaluation of Low-Temperature Phosphine Fumigation for Control of Oriental Fruit Fly in Loquat Fruit

Abstract Oriental fruit fly, Bactrocera dorsalis (Hendel; Diptera: Tephritidae), is recognized as a quarantine pest and a threat to Chinese loquat (Eriobotrya japonica Lindl.) fruit exports. Since loquat fruit is very sensitive to methyl bromide (MB) fumigation and cold treatment, in this study, low-temperature phosphine (PH3) fumigation was investigated to develop an alternative phytosanitary treatment method. Tolerance tests showed that the third instar was the most tolerant of all life stages of B dorsalis to PH3 gas at 8°C.Toxicity assay with 500–3000 ppm PH3 and subsequent probit analysis showed that 2000 ppm PH3 was optimal for fumigation and 152.75 h of treatment duration were required to achieve 99.9968% mortality. In the verification test, 144 and 168 h of treatment duration with 2000 ppm PH3 completely killed 35,277 and 35,134 B. dorsalis third instars, respectively. However, 13 live larvae were found after 120 h of treatment. Furthermore, these treatments reduced fruit respiration rates while causing no adverse effects on other fruit quality parameters, including firmness, soluble solid content, and titratable acidity over 192 h storage at 8°C. The results strongly suggest that low-temperature PH3 fumigation could be used for the postharvest control of B. dorsalis in loquat fruit.