| Under the occurrence of insects in small-scale simulated grain pile,grain bin and granary with representative height of grain heaps in China’s general grain depot,we studied the changes of CO2 concentration and quality of wheat,corn,and rice were infected by Sitophilus zeamais Mostchulsky and Rhyzopertha dominica(Fabriclus)and Cryptolestes ferrugineus(Stephens)with different insect population densities in different time,and learned the impact of pest species,grain varieties,environmental scale,detection points,etc.on the occurrence and detection value of CO2,as well as the relationship between CO2 concentration,distribution,diffusion and environmental scale.The results were as follows:The concentration of CO2 produced by C.ferrugineus with the same degree of infection was far less than S.zeamais and R.dominica in small-scale simulated grain pile,while it was produced abundant CO2 when two insects species infestation rather than single insect.In the case of a slow change of CO2 in pest free environment,even if C.ferrugineus with Low intake and metabolism at the density of 5 individuals per kg infected wheat for 9 days,the CO2 concentration increased to 0.33%,which was 2.1 times than that with no insect infestation,simultaneously,the CO2 concentration with the same density of R.dominica infestation on the sixth day was 2 times of that in wheat with no insect infestation.The main reason for the change of CO2 concentration was the number of insects increased.The development of insect population was inhibited along with increasing of CO2 concentration,a great number of insects would die and the respiration intensity of surviving insects decreased if they lived in the environment of high concentration for a long time.The CO2 concentration tended to stable when it reached about 14%,and rose slowly and steadily.The overall concentration changes showed an "S" shape.A Sample cage infected by S zeamais with the density of 10 individuals per kg was placed in wheat,corn,and rice grain bins.When CO2 concentration in the environment was about 14%,the growth rate slowed down to a stable change period.The farther away the CO2 from the center of the grain pile,the lower the detection value of CO2 concentration.The changes of concentration at different height levels are the same as those at the center level.Horizontal and vertical diffusion occur simultaneously.During the process of vertical diffusion,the trend from the occurrence point of pests to the bottom or the surface of the grain gradually decreased;meanwhile CO2 concentration and diffusion speed at the top were less than the bottom of the grain bin.In grain bin,it takes about 0.75～2 d and 0.6～1 d for CO2 to diffuse up and down 0.1m,and about 0.46 ～ 0.7 d for transverse direction diffusion of 0.1 m.A sample cage infested by S.zeamais with the density of 10 individuals per kg was placed in the center of granary with a capacity of 240 t,the volume of sample cage is 100 kg.The grain infected with pests in the sample cage was less than 0.05% of the capacity of the granary,in about two weeks;the CO2 concentration could increase by 15%.A significant increase in the concentration of CO2 was detected within 4 days at the point of occurrence of the pest,and a significant change in concentration was detected within 10 days of 5 m from the point of occurrence.The occurrence of pests in the granary significantly changed the CO2 concentration within the radius of 1 m.A temporary decreased in the CO2 concentration of each detection point when ventilate in the granary,while the concentration of the detection point around the pest occurrence increased rapidly after the granary was closed,even exceeded the concentration of CO2 before ventilation.The general open-door activity could affect the change of CO2 concentration above 2.5 m in the granary,but it did not significantly effect on the CO2 concentration at the bottom of the granary. |
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