| Resistance to phophine of Sitophilus zeamais Motschulsky,Sitophilus oryzae(Linnaeus)and Rhyzopertha dominica(Fabricius) strains collected from 17 areas in 2014 was measured by The Food and Agriculture Organization of the United Nations(FAO) recommended method. And full mortality of egg,larva,pupa and adult of the three pests of borer was assayed with 100,200,300,400 and 500 mL/m3 of phosphine concentration. The aim was to find the relationship between total lethal concentration and time. Warehouse circumstance and storage conditions and fumigation conditions of different collected unit were investigated for the answers of being resistant to phosphine. The causes of resistance to insect pests were analyzed.The results included that there was no resistance to phosphine among of three strains S.Zeamais whose LC50 ranged from 0.0066 to 0.0078 mg/L compared to the recommendation LC50. The resistance coefficients of nine strains S. Oryzae whose LC50 ranged from 0.0135 to0.3898 mg/L were less than 40 totally, and all were weak resistance. At the same time, the resistance coefficients to phosphine of nine strains R. dominica ranged from 1.0 to 173.7, and there was significant difference among strains whose LC50 ranged from 0.0083 to 1.3895mg/L.There was different in the tolerance of all stages of three susceptible strains S. zeamais to phophine.The tolerance of pupa was slightly larger than that of egg, and the tolerance of egg was slightly larger than that of larva, and the tolerance of larva was greater than that of adult.The adult mortality of three susceptible strains S. zeamais were totally more than 94%exposure for 6 h, and the adult mortality of three strains were finally 100% when the time was extended to 12 h at the concentration of 100 mL/m3 of phosphine. In the fumigation with phosphnie of 100 mL/m3 exposure time of 48 hours should be needed for full mortality of egg,larva,pupa and adult of three susceptible strains S. zeamais. The full mortality for egg,larva,pupa and adult was achieved in 24 h for fumigating with 400 mL/m3 and more. The immature stages of three strains S. zeamais could be killed by phophine in a short time, and the adult could be killed in a less time.There was different in the tolerance of all stages of four strains S. oryzae to phophine.The tolerance of pupa was slightly larger than that of egg, and the tolerance of egg was larger than that of larva, and the tolerance of larva was greater than that of adult. The adult mortality of four strains S. oryzae were different when they were exposed to 1 d at the concentration of100 ml/m3. The adult complete lethal time of 1.2,8.0,16.3 and 35.4(Rf) strains were respectively 3 d,4 d,5 d and 5 d at the concentration of 100 mL/m3, and accordingly 2 d,2 d,3d and 3 d at the concentration of 200 and 300 mL/m3 of phosphine, and accordingly 1 d,2 d,2 d and 2 d at the concentration of 400 mL/m3 of phosphine, and entirely 1 d at the concentration of 500 mL/m3 of phosphine. The results showed that the complete lethal time of egg,larva,pupa stages of the strains who had the highest and lowest resistance coefficient were respectively 9 d and 6 d at the concentration of 100 mL/m3, and accordingly 6.0 d at the concentration of 500 mL/m3 of phosphine. It is necessary to have a shorter time to kill the adult and the immature stages under high concentration, but the fumigation time could be prolonged when the fumigation concentration is lower for the complete lethal of all stages.There was different in the tolerance of all stages of four strains R.dominica to phophine.The tolerance of pupae was slightly larger than that of egg, and the tolerance of egg was larger than that of larva, and the tolerance of egg and pupa was greater than that of adult. In the fumigation with phosphnie of 100 mL/m3 exposure time of 80 min,7.5 d,9 d and 9.5 d should be needed for full mortality of adult of four strains R. dominica whose resistance coefficient were respectively 1.0,38.0,114.2 and 163.4. The adult complete lethal time of four strains R.dominica were respectively 60 min,5.5 d,5.5 d and 5.5 d at the concentration of 200 mL/m3,and accordingly 60 min,4.5 d,4.5 d and 4 d at the concentration of 300 mL/m3, and accordingly 60 min,4 d,3.5 d and 3.5 d at the concentration of 400 mL/m3, and accordingly 40 min,3.5 d,3.5 d and 3 d at the concentration of 500 mL/m3. The immature stages of three strains S. zeamais could be killed by phophine in a short time, and the adult could be killed in a less time. The results showed that the complete lethal time of the immature stages for the susceptible strain were respectively 420 min at the concentration of 100 mL/m3, and accordingly300 min at the concentration of 500 mL/m3 of phosphine. The complete lethal time of all stages of high resistant strain whose resistance coefficient was 163.4 were obviouslydifferent, and the complete lethal time of egg,larva and pupa were respectively 14.5,12.5 and15.5 d at the concentration of 100 mL/m3, and accordingly 7.0,5.0 and 7.5 d at the concentration of 500 mL/m3 of phosphine.The results show that there were individuals who were easy to death by the phosphine in the three pests of borers, and complete lethal individual number was relatively small that had a strong resistance in short-term fumigation and phosphine resistance of population was larger.Mortality of different insect stage increased with the extension of time under the same concentration, and mortality raised with increasing concentrations in the same fumigation time.Warehouse circumstance and storage conditions and fumigation conditions of different collected unit were investigated for the answers of being resistant to phosphine. The causes of resistance to insect pests were analyzed. The results showed that gas tightness,storage temperature,dosage of fumigation,closed time and fumigation concentration and the time of effective concentration were related to the pest resistance. There was no resistance to phosphine among of three S. zeamais strains which may be related to the resistance mechanism of itself.In addition to supervising the grain quality and improving the gas tightness, a variety of effective measures could delay the development of pest resistance. |
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