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Phosphine fumigation is one of the most effective way control insect pests in stored agricultural products. However, continuous use and highly dependent on phosphine fumigation has led to resistance development of major storage insect pests, including psocid. Fifty adult psocid were exposed for 20 h testing protocol to classify the susceptible to resistant strains. A full assay was composed of eight concentrations ranging from 0.003 to 1.000 g/m− 3. The most resistant strain was subjected for the extended exposure period of 72 and 144 h. Result revealed that, two out of eleven strain were still susceptible to phosphine fumigation, while nine were classified as the following: 2 strain (very low resistance), 3 strain (moderate resistance, 1 strain (high resistance) and 3 strain (very high resistance). Most susceptible was collected from La Union (lr1lug strain); LC50 and LC99 were 0.004 and 0.024 g/m− 3 concentration. Moreover, the highest resistance level was recorded in Tarlac (lr3tr strain); the LC50 and LC99 were 0.917 and 2.081 g/m− 3 concentration respectively. Based on the response of the most resistant strain and developmental stage, the projected minimum effective concentration or MEC of phosphine gas to provide a complete control of all stages of L. bostrychophila were 0.100–0.500 g/m− 3 for 72 and 144 h exposure period. The gathered data allow us to assess the importance of impending new resistance to the Philippine agricultural industry and to make an effective phosphine fumigation approaches plus resistant management strategy to fight a new strong resistance before they arise. [ABSTRACT FROM AUTHOR]

The present study evaluated the level of phosphine toxicity of various strains of Suidasia pontifica, infesting stored agricultural products in the Philippines. The bioassays for the efficacy of phosphine fumigation followed the FAO standard method. A full assay comprised eight concentrations ranging from 0.005 to 1.00 mg/L with 20, 72 and 144-h exposure periods. A total of 15 strains were collected, representing 15 provinces in the country. Results revealed that the most susceptible strain (MR12gsn) was recorded from a private owned warehouse in General Santos City—LC50 and LC99 were 0.009 and 0.025 mg/L, respectively. On the other hand, the most resistant strain (LR3tar) was collected from a private owned warehouse in Tarlac City—LC50 and LC99 were 1.501 and 2.407 mg/L, based on discrimination dose tests. Eggs were more tolerant than the adults; complete mortality of eggs was achieved at 0.50 mg/L for 72 h and 0.35 mg/L for 144 h, whereas complete mortality of adults was obtained with 0.10 and 0.20 mg/L for 144 and 72 h exposure, respectively. The estimated minimum effective concentration (MEC) of phosphine to give complete kill of S. pontifica at various exposure periods must exceed 0.50 mg/L for 72 and 144 h. These results simply illustrate the increased efficiency (i.e., increased mortality) of phosphine fumigation of longer exposure of S. pontifica to lower concentrations. [ABSTRACT FROM AUTHOR]