Correlation between Irradiation Treatment and Metabolite Changes in Bactrocera dorsalis (Diptera: Tephritidae) Larvae Using Solid-Phase Microextraction (SPME) Coupled with Gas Chromatography-Mass Spectrometry (GC-MS)

Comparison of fumigation efficacy of methyl bromide alone and phosphine applied either alone or simultaneously or sequentially against Bactrocera correcta in Selenicereus undatus (red pitaya) fruit

BACKGROUND

Bactrocera correcta (Bezzi) is a significant pest of the red pitaya fruit (Selenicereus undatus). This study investigated the insecticidal effects of methyl bromide (MB) alone, phosphine (PH3 ) alone, both applied simultaneously (PH3  + MB), and PH3 application followed sequentially by MB (PH3  → MB) against B. correcta in red pitaya fruits.

RESULTS

The 3rd instar larvae of B. correcta were the most tolerant to MB alone and the combined treatments, whereas eggs were the most susceptible stage. Both the PH3  + MB and PH3  → MB treatments resulted in higher mortality at all stages than MB alone, demonstrating a synergistic effect between MB and PH3 . The toxicity of the combined treatments increased with increasing PH3 concentrations, with the optimal concentration recorded being 1.42 to 2.84 g m-3 . Further probit analysis revealed that compared to the MB treatment alone, the median lethal dose values of MB in PH3  + MB and PH3  → MB treatment, were reduced to 63.73% and 66.82%, respectively. Fruit quality was not adversely affected by either of the combined treatments.

CONCLUSION

This work provides robust evidence that combining MB and PH3 to control B. correcta is highly effective, especially the PH3  → MB treatment. This combination decreased the amount of MB required for effective control at all life stages, while protecting fruit quality against MB phytotoxicity to a greater extent than conventional MB fumigation alone. © 2023 Society of Chemical Industry.

Comparative Analysis of the Metabolic Profiles of Strains of Tribolium castaneum (Herbst) Adults with Different Levels of Phosphine Resistance Based on Direct Immersion Solid-Phase Microextraction and Gas Chromatography-Mass Spectrometry

The management of phosphine (PH3) resistance in stored grain pests is an essential component of implementing timely and effective pest control strategies. The prevailing standard method for PH3 resistance testing involves the exposure of adult insects to a specific concentration over a fixed period. Although it is widely adopted, this method necessitates an extensive period for assay preparation and diagnosis. To address this issue, this study employed Direct Immersion Solid-Phase Microextraction (DI-SPME) coupled with Gas Chromatography-Mass Spectrometry (GC-MS) to compare and analyze the metabolic profiles of PH3-sensitive (TC-S), PH3 weak-resistant (TC-W), and PH3 strong-resistant (TC-SR) Tribolium castaneum (Herbst) adults. A total of 36 metabolites were identified from 3 different PH3-resistant strains of T. castaneum; 29 metabolites were found to present significant differences (p < 0.05) across these groups, with hydrocarbon and aromatic compounds being particularly prevalent. Seven metabolites showed no significant variations among the strains, consisting of four hydrocarbon compounds, two iodo-hydrocarbon compounds, and one alcohol compound. Further multivariate statistical analysis revealed a total of three, two, and nine differentially regulated metabolites between the TC-S versus TC-W, TC-S versus TC-SR, and TC-W versus TC-SR groups, respectively. Primarily, these metabolites comprised hydrocarbons and iodo-hydrocarbons, with the majority being associated with insect cuticle metabolism. This study demonstrates that DI-SPME technology is an effective method for studying differentially expressed metabolites in T. castaneum with different levels of PH3 resistance. This approach may help to provide a better understanding of the development of insect PH3 resistance and act as a valuable reference for the establishment of rapid diagnostic techniques for insect PH3 resistance.