Development and Metabolomic Profiles of Bactrocera dorsalis (Diptera: Tephritidae) Larvae Exposed to Phytosanitary Irradiation Dose in Hypoxic Environment Using DI-SPME-GC/MS

Abstract

X-ray irradiation and modified atmospheres (MAs) provide eco-friendly, chemical-free methods for pest management. Although a low-oxygen atmospheric treatment improves the performance of some irradiated insects, its influence on the irradiation of quarantine insects and its impacts on pest control efficacy have yet to be investigated. Based on bioassay results, this study employed direct immersion solid-phase microextraction (DI-SPME) combined with gas chromatography-mass spectrometry (GC-MS) to determine metabolic profiles of late third-instar B. dorsalis larvae under normoxia (CON, Air), hypoxia (95% N₂ + 5% O₂, HY), super-hypoxia (99.5% N₂ + 0.5% O₂, Sup-HY), irradiation-alone (116 Gy, IR-alone), hypoxia + irradiation (HY + IR) and super-hypoxia + irradiation (Sup-HY + IR). Our findings reveal that, compared to the IR-alone group, the IR treatment under HY and Sup-HY (HY + IR and Sup-HY + IR) increases the larval pupation of B. dorsalis, and weakens the delaying effect of IR on the larval developmental stage. However, these 3 groups further hinder adult emergence under the phytosanitary IR dose of 116 Gy. Moreover, all IR-treated groups, including IR-alone, HY + IR, and Sup-HY + IR, lead to insect death as a coarctate larvae or pupae. Pathway analysis identified changed metabolic pathways across treatment groups. Specifically, changes in lipid metabolism-related pathways were observed: 3 in HY vs. CON, 2 in Sup-HY vs. CON, and 5 each in IR-alone vs. CON, HY + IR vs. CON, and Sup-HY + IR vs. CON. The treatments of IR-alone, HY + IR, and Sup-HY + IR induce comparable modifications in metabolic pathways. However, in the HY + IR, and Sup-HY + IR groups, the third-instar larvae of B. dorsalis demonstrate significantly fewer changes. Our research suggests that a low-oxygen environment (HY and Sup-HY) might enhance the radiation tolerance in B. dorsalis larvae by stabilizing lipid metabolism pathways at biologically feasible levels. Additionally, our findings indicate that the current phytosanitary IR dose contributes to the effective management of B. dorsalis, without being influenced by radioprotective effects. These results hold significant importance for understanding the biological effects of radiation on B. dorsalis and for developing IR-specific regulatory guidelines under MA environments.

Keywords: Bactrocera dorsalis; SPME technology; development; irradiation; metabolites; modified atmosphere; radioprotective effects.

Figure 1

Schematic diagram of the technical process for the development test of the late third-instar B. dorsalis (Diptera: Tephritidae) larvae under different treatment conditions (Control, HY, Sup-HY, IR, HY + IR, and Sup-HY + IR).

Figure 2

Proportion of B. dorsalis (Diptera: Tephritidae) larvae in the control (A(1)), hypoxia (A(2)), super hypoxia (A(3)), irradiation (B(1)), hypoxia + irradiation (B(2)) and super-hypoxia + irradiation (B(3)) treatment groups.

Figure 3

Heatmap displaying the abundance changes of the metabolites significantly influenced by different treatment methods, with significance determined via one-way ANOVA at p < 0.05.

Figure 4

PCA score plot of the metabolic profiles in the B. dorsalis (Diptera: Tephritidae) larvae exposed to different MAs under IR (116 Gy).

Figure 5

PLS-DA score plot of the metabolic profiles in the B. dorsalis (Diptera: Tephritidae) larvae exposed to different MAs under IR (116 Gy).

Figure 6

A variable importance plot showing the contribution of each metabolite to the first component (ranked by VIP scores) in the CON vs. IR (A), CON vs. HY (B), CON vs. Super-HY (C), CON vs. HY + IR (D), and CON vs. Sup-HY + IR (E) groups.

Figure 7

Edward’s Venn diagram of the CON vs. IR, CON vs. HY, CON vs. Sup-HY, CON vs. HY + IR, and CON vs. Sup-HY + IR groups. Different colors represent 5 groups of data sets, and numbers indicate the quantity of elements in the overlapping areas.

Figure 8

Metabolome view map of the significant metabolic pathways characterized in the B. dorsalis (Diptera: Tephritidae) larvae exposed to different modified atmospheres under a phytosanitary irradiation dose. (A) CON vs. IR-alone, (B) CON vs. HY, (C) CON vs. Sup-HY, (D) CON vs. HY + IR, and (E) CON vs. Sup-HY + IR.

Figure 9

(A) The integrated schematic diagram of the key metabolic pathways and metabolites in the B. dorsalis (Diptera: Tephritidae) larvae exposed to different modified atmospheres under a phytosanitary irradiation dose, and (B) the changes in peak areas of 5 key compounds ((a). tetradecanoic acid, (b). n-hexadecanoic acid, (c). octadecanoic acid, (d). oleic acid and (e). squalene) across different treatment conditions.