Fumigation of fruits and vegetables during quarantine and pre-shipment (QPS) treatment should be effective with a shorter fumigation time to minimize phytotoxicity. In this research study, a shorter fumigation time, 2 hours exposure which is shorter than that of the current commercial fumigation procedures using a lower dose of ethyl formate (EF) mixed with phosphine (PH3) on strawberry was investigated. The reciprocal effect between EF and PH3 against nymphs and adult Myzus persicae (Sulzer) and Tetranychus urticae (Koch) was evaluated. In addition, L(Ct)50 and L(Ct)99 of EF only and EF mixed with PH3 were analyzed at 5°C and 20°C. The synergistic ratio (SR) of L(Ct)50 and L(Ct)99 for the nymph and adult stages of M. persicae were >1.0, which indicated a synergistic effect between EF and PH3. However, the SR values of L(Ct)50 and L(Ct)99 of the nymph and adult stages of T. urticae were ≤1.0 indicating that there was no synergistic effect between the two fumigants against T. urticae. Our results showed that the reciprocal effect between EF and PH3 has different effects on M. persicae and T. urticae. This could be attributed to the biological and physical differences between the class Arachnida and Insecta. The synergistic effect between EF and PH3 against M. persicae within a shorter exposure period and without phytotoxicity on fruits and vegetables will significantly benefit the horticultural industry.

Stored grain pests can cause reduction of grain quantity, quality, commercial value and germination rate. Susceptibility of three fumigants, methyl bromide, ethyl formate and phosphine, were assessed on Tribolium castaneum, which is an important stored grain pest. On susceptible insects, LCT50 of phosphine was 0.654mg h/L for egg, 0.127mg h/L for late larvae, 0.105mg h/L for pupae and 0.048mg h/L for adult stage, respectively. LCT50 of methyl bromide was 33.193mg h/L for egg, 14.585mg h/L for late larvae, 8.616mg h/L for pupae and 11.967mg h/L for adult stage, respectively. LCT50 of ethyl formate were 25.165mg h/L for egg, 80.912mg h/L for late larvae, 176.326mg h/L for pupae and 68.578mg h/L for adult stage, respectively. On resistant insects, LCT50 of phosphine were 82.325mg h/L for egg, 33.315mg h/L for late larvae, 73.546mg h/L for pupae and 55.707mg h/L for adult stage, respectively. LCT50 of methyl bromide were 19.250mg h/L for egg, 43.413mg h/L for late larvae, 76.842mg h/L for pupae and 19.387mg h/L for adult stage, respectively. LCT50 of ethyl formate were 87.552mg h/L for egg, 113.457mg h/L for late larvae, 200.122mg h/L for pupae and 85.394mg h/L for adult stage, respectively.

The respiration rate of PH3 susceptible strain was significantly higher than the resistant strain. The results showed no significant effect of oxygen level on the respiration rate of both strains. Phosphine reduced the respiration rate of both strains when it was applied in average concentrations. However, the rate of respiration of the resistant beetles increased significantly under a high level of phosphine. The increase of respiration rate was associated with the higher emission of VOCs which prove the acceleration of metabolic processes to face the phosphine action for survival. Flat grain beetle Cryptolestes pusillus and rusty grain beetle C. ferrugineus are similar insect species, but only C. ferrugineus is capable to develop a high phosphine resistance. A direct immersion solid phase microextraction gas chromatography-mass spectrometry (DI-SPME-GCMS) technology has identified the different fatty acids from PH3 resistant and susceptible strain of Tribolium castaneum.

Phosphine (PH3) resistance in the stored-products insect pests has been reported throughout the world in various insect species, including Rhyzopertha dominica, Tribolium castaneum, and Cryptolestes ferrugineus, leading farmers and fumigators to identify new fumigation tools to control PH3-resistant insect pests in storage facilities. Understanding PH3-resistance mechanisms in insects might contribute to providing clues for the development of new chemicals, including fumigants, to control various PH3-resistant insects. A proteomic study has shown 15 decreased proteins in the PH3-resistant R. dominica (CRD343 strain) in comparison to the PH3-susceptible R. dominica, and among those 15 proteins, dihydrolipoamide dehydrogenase (DLD), a protein involved in the Krebs cycle, was identified (Park et al., 2008). The DLD polymorphisms responsible for genetic resistance have disulfide active sites for PH3 binding and are highly sensitive to arsenic exposure after mutagenesis in insects (R. dominica and T. castaneum) and Caenorhabditis elegans (Schlipalius et al., 2012). Here, two PH3- resistant S. oryzae strains were used to understand the development of PH3 resistance in these insects. Acute toxicity test by PH3 on the two PH3-resistant strains was undertaken followed by ethyl formate inhibition study on cytochrome c oxidase activity. The Lineweaver-Burk plots after inhibition studies showed there were significantly difference in inhibition mode between the resistant strains and the control. The RT-qPCR analysis and the next-generation sequencing of the mitochondrial DNA revealed significant changes in metabolism and energy production. Taken together, the PH3 resistance in S. oryzae was definitely acquired by the overall transformation of biochemical reactions to overcome PH3 toxicity.

Fumigation - one of the chemical methods - is the art of dispensing and applying gaseous substances especially for the purpose of disinfecting. It is an old and widely used technique for disinfestation of postharvest grain, fruit and vegetable. In a fumigation procedure, a gas is added to an enclosure for the purpose of controlling or eliminating undesirable organisms. The organisms may be pests of various types - such as insects, rodents, mites, and birds - or micro-organisms, or particular plants or seeds. The enclosure can be made from a diverse range of materials, including metal, concrete, bricks, mud and various plastic membranes. It is necessary to contain the fumigant while it acts on the target organism and to restrict its escape into areas where it may be dangerous to human health. In many situations fumigation may be the only feasible process for pest control as it does not require the commodity to be moved. Neither might it need specialized apparatuses, electricity, or manpower, and is relatively easy to apply in comparison with other methods, for example, heating and irradiation, as well as the use of protectants to control insects. Because fumigation is often the cheapest and most effective process available, it plays a major, world-wide, role in preserving commodities. However, researchers and operators not always fully understand principle of fumigant and fumigation practice to ensure select right fumigant and exposure time on different target insect pests and host commodities as well as application methods.

Ethyl formate (EF) and methyl salicylate (MS) are naturally occurring and generally safe substances for use. Sub-lethaldoses of EF and MS were evaluated to find synergistic fumigation action against azuki bean beetle (ABB), Callosobruchuschinensis (L.). Susceptibility of the ABB to EF was in the order of eggs =adults >larvae >pupae. Adults was most sensitiveto MS, and followed by eggs. Larvae and pupae were highly tolerant to MS. However, in synergistic effects of EF andMS showed that all the stages of ABB were highly sensitive in the order of adults >eggs >larvae >pupae. Highest synergisticratio was found against adults when using LC10 of both EF and MS as compared to other stages. Notably, MS synergizedthe EF exposure to all stages of ABB. This finding paves the way to exploiting synergistic activity of MS and EF againstABB for the safeguard of stored azuki bean grains.