Variation of carbon dioxide concentration in the microenvironment of paddy rice,brown rice,and milled rice infested by hidden pest,Sitophilus zeamais Mostchulsky
Early detection and treatment of hidden insect pests in grain can prevent grain losses.Understanding the relationship between carbon dioxide produced by the metabolism of pests in hidden life stages and infestation levels in cereals is helpful for rapid detection.Paddy rice,brown rice,and milled rice containing Sitophilus zeamais Mostchulsky eggs,first instar larvae,second instar larvae,third instar larvae,pupae,and adults in kernels mixed into insect-free paddy rice,brown rice,and milled rice at densities of 0,5,10,and 20 larvae per kilogram of grain were measured for carbon dioxide concentration.The carbon dioxide concentration in insect-free cereal bulk was only 0.04％.In the stored microenviroment of paddy rice,brown rice,and milled rice containing SS.zeamais at densities of 5,10,and 20 larvae per kilogram of cereals,the carbon dioxide concentration ranged from 0.042％to 0.055％for eggs and first instar larvae infestation.For second instar larvae infestation corresponded to 5,10,and 20 larvae per kilogram of cereals,the carbon dioxide concentrations were 0.127％,0.246％,and 0.425％in paddy rice;0.145％,0.234％,and 0.483％in brown rice;and 0.134％,0.246％,and 0.438％in milled rice,respectively.For third instar larvae infestation,carbon dioxide concentrations were 0.292％,0.425％,and 0.677％in paddy rice;0.303％,0.482％,and 0.670％in brown rice;and 0.292％,0.463％,and 0.668％in milled rice.For pupa infestation,the carbon dioxide concentrations were 0.095％,0.237％,and 0.381％in paddy rice;0.082％,0.223％,and 0.430％in brown rice;and 0.096％,0.235％,and 0.385％in milled rice.For adult infestation in kernels,carbon dioxide concentrations were 0.125％,0.215％,and 0.494％in paddy rice;0.151％,0.235％,and 0.557％in brown rice;and 0.131％,0.221％,and 0.503％in milled rice.The results indicate that when paddy rice,brown rice,and milled rice were infested by SS.zeamais,carbon dioxide concentrations can be detected within 24 h,and concentrations below 0.15％correspond to light infestations of immature stages(excluding pupal stage),concentrations between 0.2％and 0.4％resulted in moderate infestation(corresponding to second instar larvae,10 larvae per kilogram cereals),and concentrations exceeding 0.55％caused heavy infestations(corresponding to third instar larvae stage,20 larvae per kilogram rice).Significant changes can also be detected in moderate and heavy infestations within 12 h.Brown rice was found to be the most susceptible to S.zeamais larvae,with higher carbon dioxide production,followed by milled rice and paddy rice.
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