Efficacy of vaporised ethyl formate/carbon dioxide formulation against stored-grain insects: effect of fumigant concentration, exposure time and two grain temperatures

A New Approach: Ethyl Formate Fumigation to Control Bemisia tabaci (Hemiptera: Aleyrodidae) in a Yellow Melon Vinyl House

Due to concerns over the resistance development to existing pesticides, chemical poisoning among farmers, and chemical residue on crops, sprung up a growing need to develop new pest control strategies for utilization in protected houses in Korea. A series of experiments tested a new technology using a fumigant, ethyl formate, in growing crops in the protected houses. It was revealed that the glasshouse was inadequate for the fumigation system using the fumigant since ethyl formate gas sharply decreased due to gas leaking through the gaps between the glass frames. On the other hand, the gas concentration was stable during the fumigation process. Experiments were also conducted to evaluate its phytotoxicity on cucurbits crops (yellow melon). The crops were fumigated at 20 °C in three fumigation schedules (2, 4, and 12 h). The results revealed that the developmental stages of yellow melon showed no sign of phytotoxicity in all conditions. However, the fumigation damaged the shoots of red pepper in higher humidity and at a longer duration. Interestingly, Bemisia tabaci were (100%) completely killed in all these conditions. Based on the results of the above experiments on the high efficacy on the control of Bemisia tabaci and zero phytotoxic effects of the ethyl formate fumigation on yellow melon, verification experiments for the effectiveness were conducted thrice in farmer’s yellow melon vinyl houses and once in a farmer’s cucumber vinyl house. Results demonstrated that ethyl formate fumigation for 2 h at 2 g m−3 concentration could 100% kill the adults of Bemisia tabaci with no phytotoxic effect on the crops. Therefore, we could conclude that the 2-h fumigation system with 2 g m−3 ethyl formate would be a new alternative to the existing chemical spraying methods.

Responses of Fungi Maggot (Bradysia impatiens Johannsen) to Allyl Isothiocyanate and High CO2

Botanical pesticide is highly recommended for integrated pest management (IPM), due to its merits such as environmental friendliness, safe to non-target organisms, operators, animals, and food consumers. The experiment was conducted to determine the lethal and sub-lethal effects of allyl isothiocyanate (AITC) on eggs, third instar larvae, pupae, and females and males of Bradysia impatiens Johannsen (B. impatiens). Different concentrations of AITC under ambient CO₂ by the conical flask sealed fumigation method were used for the experiment. The results showed that there was a significant linear relationship between different concentrations of AITC and the toxicity regression equation of B. impatiens. The sub-lethal concentrations of AITC had significant effects on the larval stage, pupal stage, pupation rate, pupal weight, adult emergence rate, and oviposition. The pupation rate, pupal weight, and adult emergency rate were significantly (p < 0.05) affected by AITC fumigation. The pupation rate was the lowest after fumigation treatment of AITC at LC₅₀ (36.67%), followed by LC₂₅ (41.94%), compared with the CK (81.39%). Female longevity was significantly (p < 0.05) shortened by fumigation at LC₂₅ (1.75 d) and LC₅₀ (1.64 d), compared with that of CK (2.94 d). Male longevity was shorter at LC₂₅ (1.56 d) than at LC₅₀ (1.25 d) and had no significant difference between these two treatments. The fumigation efficiency of AITC was significantly increased under high CO₂ condition. Furthermore, detoxification enzyme activities and antioxidant enzyme activities were accumulated under high CO₂ condition. The fumigation method in the application of AITC can be useful in areas where B. impatiens is a major concern.

A co-fumigation strategy utilizing reduced rates of phosphine (PH3 ) and sulfuryl fluoride (SF) to control strongly resistant rusty grain beetle, Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae)

BACKGROUND

Managing resistance to phosphine (PH₃ ) in rusty grain beetle, Cryptolestes ferrugineus, is challenging, as strongly resistant insects of this species require very high concentrations over lengthy exposure periods (>10 days). Recently, approaches that enhance the efficacy of PH₃ have gained momentum to control this pest, especially co-fumigations. In this study, efficacy of co-fumigating PH₃ with another commercially available fumigant, sulfuryl fluoride (SF), has been evaluated against adults and eggs of two PH₃ -resistant strains of C. ferrugineus. Concentrations of the mixture, representing lower than current application rates of both fumigants, were tested towards its field use.

RESULTS

Co-fumigation of PH₃ with SF was achieved in two patterns: over a continuous exposure period of 168 h simultaneously and sequentially over two periods of 78 h, in which insects were exposed to SF first followed by PH₃ with 12 h aeration in-between. Results of simultaneous fumigations identified two effective co-fumigation rates, SF 185 + PH₃ 168 g hm^-3 and SF 370 + PH₃ 84 g hm^-3 that yielded complete control of adults and eggs. These two rates also were equally effective when they were applied sequentially and produced consistent results. Irrespective of application methods, concentrations of both PH₃ and SF failed individually in achieving complete mortality of either adults or eggs or both.

CONCLUSION

Our results confirmed that a co-fumigation strategy involving half the current standard rate of PH₃ (84 g hm^-3 ) with one-fourth of the current maximal registered rate of SF (370 g hm^-3 ) can provide effective control of strongly PH₃ -resistant C. ferrugineus.

Synergistic Effects of Oxygen on Phosphine and Ethyl Formate for the Control of Phthorimaea operculella (Lepidoptera: Gelechiidae)

Phosphine (PH3) and ethyl formate (EF) are two potentially powerful postharvest fumigant insecticides. We investigated the effectiveness of both PH3 and EF as fumigants at all developmental stages of the potato tuber moth Phthorimaea operculella Zeller, and we also studied the synergistic effects of these fumigants under controlled atmospheres of 50 and 80% oxygen (O2). The larval stage of P. operculella was the most susceptible to fumigation with PH3 at both 5°C and 20°C. All of the developmental stages showed greater susceptibility to PH3 at 20°C than at 5°C, whereas the susceptibility of adult P. operculella to this fumigant was not affected by temperature. The toxicity of EF did not differ with temperature for any of the P. operculella developmental stages. The atmospheric oxidation of PH3 increased the toxicity of this fumigant toward all developmental stages at both temperatures. In contrast, no differences in toxicity were observed for oxidized EF compared with EF alone at any developmental stage. In conclusion, using fumigation tests, we showed that atmospherically oxidized PH3 was much more effective against P. operculella than PH3 alone, demonstrating a synergistic effect for this fumigant and O2. Therefore, treatment with PH3 and high concentrations of O2, as described in this study, could be useful for managing the postharvest pest P. operculella.

Developing effective fumigation protocols to manage strongly phosphine-resistant Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae)

BACKGROUND

The emergence of high levels of resistance in Cryptolestes ferrugineus (Stephens) in recent years threatens the sustainability of phosphine, a key fumigant used worldwide to disinfest stored grain. We aimed at developing robust fumigation protocols that could be used in a range of practical situations to control this resistant pest.

RESULTS

Values of the lethal time to kill 99.9% (LT99 .9 , in days) of mixed-age populations, containing all life stages, of a susceptible and a strongly resistant C. ferrugineus population were established at three phosphine concentrations (1.0, 1.5 and 2.0 mg L(-1) ) and three temperatures (25, 30 and 35 °C). Multiple linear regression analysis revealed that phosphine concentration and temperature both contributed significantly to the LT99 .9 of a population (P < 0.003, R2 = 0.92), with concentration being the dominant variable, accounting for 75.9% of the variation. Across all concentrations, LT99.9 of the strongly resistant C. ferrugineus population was longest at the lowest temperature and shortest at the highest temperature. For example, 1.0 mg L(-1) of phosphine is required for 20, 15 and 15 days, 1.5 mg L(-1) for 12, 11 and 9 days and 2.0 mg L(-1) for 10, 7 and 6 days at 25, 30 and 35 °C, respectively, to achieve 99.9% mortality of the strongly resistant C. ferrugineus population. We also observed that phosphine concentration is inversely proportional to fumigation period in regard to the population extinction of this pest.

CONCLUSION

The fumigation protocols developed in this study will be used in recommending changes to the currently registered rates of phosphine in Australia towards management of strongly resistant C. ferrugineus populations, and can be repeated in any country where this type of resistance appears.

Ethyl formate plus methyl isothiocyanate--a potential liquid fumigant for stored grains

BACKGROUND

Methyl bromide is being phased out for use on stored commodities, as it is listed as an ozone-depleting substance, and phosphine is the fumigant widely used on grains. However, phosphine resistance occurs worldwide, and phosphine fumigation requires a long exposure period and temperatures of >15 °C. There is an urgent requirement for the development of a fumigant that kills insects quickly and for phosphine resistance management. This paper reports on a new fumigant formulation of 95% ethyl formate plus 5% methyl isothiocyanate as an alternative fumigant for stored grains.

RESULTS

The formulation is stable for at least 4 months of storage at 45 °C. A laboratory bioassay with the formulation showed that it controlled all stages of Sitophilus oryzae (L.), Sitophilus granarius (L.), Tribolium castaneum (Herbst), Rhyzopertha dominica (F.), Trogoderma variabile Ballion and Callosobruchus maculatus (Fabricius) in infested wheat, barley, oats and peas at 80 mg L(-1) for 5 days, and in canola at both 40 mg L(-1) for 5 days and 80 mg L(-1) for 2 days at 25±2 °C. After an 8-14 day holding period, residues of ethyl formate and methyl isothiocyanate in wheat, barley, peas and canola were below the experimental permit levels of 1.0 and 0.1 mg kg(-1). However, fumigated oats needed an 18 day holding period.

CONCLUSIONS

The findings suggest that the ethyl formate plus methyl isothiocyanate formulation has potential as a fumigant for the control of stored-grain insect pests in various commodities.