## 4 Discussion  
There are more than 60 species of mealybug worldwide, and _P. citri_ is a major pest of citrus [33]. This pest is currently controlled for the protection of fruits from damage during the cultivation of orange, grapefruit, lemon, and mandarin using chemical insecticides such \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & & & \multicolumn{3}{c}{**Assignment**} & \multicolumn{3}{c}{**Average Intensity Value**} \\ \cline{4-9}
**No** & _m/z_ **Value** & **Delta** & **[M-H]** & **Con** & **PH3** & **EF** & **EF + PH3** \\ \hline
1 & 699.4970 & 0.000038 & PA(O-16:0) & 551.7 & 454.9 & 151.2 & 41.4 \\
2 & 740.5180 & 0.005587 & PC(P-20:0) & 569.6 & 460.0 & 237.0 & 50.7 \\
3 & 742.5392 & 0.000037 & PC(O-20:0) & 1618.6 & 1189.4 & 678.5 & 39.8 \\
4 & 784.5134 & 0.000017 & PC(14:0) & 237.8 & 212.0 & 81.1 & 26.0 \\
5 & 820.5265 & 0.008047 & PS(18:0) & 94.1 & 84.2 & 48.7 & 24.5 \\
6 & 833.4822 & 0.000022 & PG(16:1) & 678.2 & 552.7 & 245.8 & 26.0 \\
7 & 837.4407 & 0.000008 & PI(20:0) & 100.6 & 77.7 & 41.9 & 23.4 \\
8 & 857.4976 & 0.000167 & PG(20:3) & 571.8 & 497.8 & 294.7 & 27.0 \\
9 & 859.5425 & 0.008287 & PI(O-16:0) & 3970.8 & 3389.5 & 1630.5 & 34.3 \\
10 & 860.5447 & 0.000017 & PC(18:2) & 2484.6 & 2088.0 & 778.9 & 203.6 \\
11 & 862.5604 & 0.000033 & PC(18:1) & 5549.8 & 4745.0 & 1654.6 & 408.9 \\
12 & 699.4970 & 0.000038 & PA(O-16:0) & 551.7 & 454.9 & 151.2 & 41.4 \\
13 & 740.5180 & 0.005587 & PC(P-20:0) & 569.6 & 460.0 & 237.0 & 50.7 \\
14 & 742.5392 & 0.000037 & PC(O-20:0) & 1618.6 & 1189.4 & 678.5 & 39.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: List of significant lipid estimated m/z values detected using MALDI-TOF MS with the negative ion mode (Kruskal–Wallis Test (Pr > Chi-square, \(p\) < 0.0001)). Figure 5: Mass ions for lipid profiling on _P. citri_ adults after exposure to ethyl formate (EF), phosphine (PH3), and combination treatment (EF + PH3) for 4 h. (**a**) Spectrums of MALDI-TOF MS. (**b**) Pairwise analysis using a heatmap with the Kruskal\(-\)Wallis test (_p_ < 0.0001). A heatmap was constructed using the Log2 intensity ratio between the control and treatment groups. as chlorpyrifos, chlorpyrifos-ethyl, methidathion, malathion, imidaloprid, buprofezin, and spirotetramat [34]. Although pest control of fruits using chemical insecticides during cultivation has been successfully performed, there is a presumable hindrance found in post-harvest management using MB and alternatives, including quarantine. MB can be completely replaced only when a clear combination treatment efficacy and mechanism of action are evaluated. The efficacy of combination treatment of PH\({}_{3}\) with EF has been evaluated in several studies [1,7,35], but there is a lack of understanding of the mechanisms. PH\({}_{3}\) is used as the most global alternative fumigant to MB, but there are still some issues to be solved: a relatively long treatment time with slow activity and high resistance [8]. When the PH\({}_{3}\) treatment time was changed from 20 h to 4 h, the efficacy of _P. citri_ on the eggs showed a mortality rate of 60% at the highest concentration of 4 mg/L PH\({}_{3}\) (Table 1 and Table S3). On the other hand, EF has a concentration of 285-1536 times higher than PH\({}_{3}\) based on LC\({}_{50}\) values (Table 1 and Table S1). Nevertheless, as _P. citri_ is an invasive species, it is an important pest that prohibits transfer between countries. Thus, appropriate quarantine systems should be in operation in each country to prevent their spread. MB is minimally used for quarantine and pre-shipment, but MB substitutes are continuously developed and used selectively in the field [7]. According to [PERSON] et al. (2016), the fumigation control of _P. citri_ was reported using EF and PH\({}_{3}\) for quarantine. The LCT\({}_{99}\) values were obtained using a 55 L fumigation chamber, and EF exhibited the LCT\({}_{99}\) values 211.04, 49.51, and 124.61 mg\(\cdot\)h/L for eggs, nymphs, and adults, respectively [7]. These results are slightly different from those obtained in this study.