## 1 Introduction  
Phosphine (PH\({}_{3}\)) is now probably the most widely used fumigant in the world at present to disinfect stored products [1] after the decreased use of methyl bromide, which depletes the ozone layer [2, 3]. Phosphine can also be applied directly to a commodity, is easy to obtain, easy to use, and relatively inexpensive [4, 5]. Additional positive attributes of phosphine use include its residue-free nature when used as a treatment and effectiveness against insect pests at all developmental stages, including eggs; however, phosphine requires longer exposure periods (within commercial reality) than other disinfectants to exhibit toxicity, particularly against highly PH\({}_{3}\)-resistant insects [6]. Resistant populations are divided into two groups depending on the phenotype: a \"weak resistance\" group and a \"strong resistance\" group. Strong resistance to phosphine occurs because of two loci that work in synergy, the _rph1_ (resistance to phosphine) and _rph2_ genes, which are responsible for phosphine resistance in _Rhyzopertha domica_[7, 8], _Tribolium castaneum_[9] and _Stiophilus oryzae_[10, 11]. Among these, in particular, high-level resistance to phosphine in _S. oryzae_ has been reported in India, China, Morocco, Brazil, and Australia [12, 13, 14, 10]. _Stiophilus oryzae_ causes damages to stored products and its contamination of grain products has become a major problem in cereal market. Resistance to phosphine in _S. oryzae_ had increased to 75% in developing countries by 2000 [10], requiring the management of resistance. To replace or reduce the usage of insecticides, environmentally friendly alternatives have been developed. One of them is the modified atmosphere (MA) technology [15, 16, 17]. [PERSON] et al. evaluated that heat shock protein and ATP synthase \(\beta\) subunit were overexpressed in _R. dominica_ exposed to MA by LC MS/MS [17].  
Genomics reveals what genes are present, while transcriptomics shows how active genes are in different cells. These strategies have contributed tremendously to accelerating the discovery of phosphine resistance-associated genes [18]; however, such advances cannot reveal the complexities of protein biochemistry, including protein abundance. Proteomic analysis can help to analyze different protein synthesis changes at the molecular level [19; 20]. Furthermore, understanding PH\({}_{3}\)-resistance mechanisms in insects may contribute to providing clues for the development of new chemicals, including fumigants to control PH\({}_{3}\)-resistant insects. A proteomic study has shown differences of protein expression in a PH\({}_{3}\)-resistant _R. dominica_ in comparison to a PH\({}_{3}\)-susceptible _R. dominica_ and among them dihydroamide dehydrogenase, a protein involved in the Krebs cycle, has been identified [21]. Additionally, [PERSON] et al. reported the ethyl formate fumigation caused lethal effects on _Myuzus persicae_ nymphs by changing cytochrome c oxidase (COX) activity, acetylcholinesterasecholinesteraseerase (AChE) gene expression, and phospholipid production [22]. They analyzed the lipid content using MALDI-TOF MS/MS. Recently, [PERSON]'s study using RT-PCR for the determination of mitochondrial gene expression in PH\({}_{3}\)-resistant _Cryptolestes ferrugineus_ has demonstrated that _cox1_ expression was not significantly different when compared to a PH\({}_{3}\)-susceptible _C. ferrugineus_, while _nad3_, _atp6_, and _cob_ genes were down-regulated [23]. This pattern is different from other studies [21]. Therefore, PH\({}_{3}\) resistance is dependent on insect species and associated with the modulation of energy production in mitochondria.  
This study aimed to compare differences in the protein expression of the PH\({}_{3}\)-R and PH\({}_{3}\)-S strains of _S. oryzae_ using 2D-PAGE and MALDI-TOF/TOF. The results clarify phosphine resistance mechanism, allowing the development of more reliable, sensitive, and useful molecular markers to monitor rice weevil phosphine resistance.