| Mythimna loreyi(Duponchel)is belonged to Noctuidae of Lepidoptera,which is closely related to a species,Mythimna separata(Walker).Both of them often occur mixed in the food crop fields,in particular,the damage to corn is the most serious,and pose a severe threat to food security production.Therefore,it is essential to pest control and to ensure the safety of agricultural production.This paper mainly studied the influence of larval density on the biological parameters,main energy metabolites and related enzymes in M.loreyi.The mechanism of population regulation of the armyworm is revealed to provide theoretical basis for prediction and forecasting.In this experiment,six larval densities was set,such as 1,10,20,30,40,and 50larvae/cassette.The growth,development and reproduction of M.loreyi at different densities were observed and recorded.The content of water,glycogen,trehalose,andfat body,as well as the activity of HOAD enzyme were measured from the 6th instar larva,pupa,the moth freshly emerged(eclosion)and 1-7 days adult of M.loreyi.The main results were as follows:1. Along with the increase of larval density,both larval and pupal periods illustrated a decreasing tendancy first and then rose,and reached the lowest point at 10 larvae/cassette.In contrast,pupa weight tended to rise first and then gradually dropped,and peaked at 10larvae/cassette.Over-high or low larval density would lead to a decrease in pupa weight.The survival rate of larvae enhanced first and then diminished with the increasing density,while the rate of pupa stayed declining.Under the condition of medial and low density,larval and pupa survival rate of M.loreyi were all kept at a high level.As the density was over-high,all of these parameters reduced significantly.2. With the increase of the density of larvae,the daily oviposition peak of females tended ahead of time,and the peak first increased and then decreased.Under the condition of20 larvae/cassette,the egg laying amount of adult was the largest with 395.93 eggs,which was significantly higher than other density treatments.Over-high or low density was unfavorable to oviposition of M.loreyi.3. There was a parabolic trend between the population growth index and the larval density of M.loreyi:y=-0.0672x~2+2.1859x+174.416(R2=0.9405).With the density of 10larvae/cassette,the armyworm had a high survival rate and a strong reproductive ability,and its population growth index was the highest,which was 97.63.The population density promoted growth and was favorable to the population reproduction.Under the condition of high density,the population growth index decreased evidently,and the index was the lowest at 50 larvae/cassette,which was only 21.71.4. Under the condition of 50 larvae/cassette,the water content of M.loreyi at each developmental stage was remarkably lower than others.The effect of larval density on the glycogen content from larva to the moth freshly emerged of M.loreyi was primarily observed under the condition of 50 larvae/cassette density,which was significantly lower than other density treatments.The contents both of glycogen and trehalose were the highest in pupal stage.A certain density of larvae(30 larvae/cassette)was beneficial to the accumulation of total fat,however,the fat body content decreased when the density was over-high.5. The activities of HOAD enzyme were low in larva,pupa and the moth freshly emerged,and increased rapidly until 3-days-old adult.Under different density conditions,the HOAD enzyme activity in 1-7 days-old-adults showed the similar trend,and all indicated rising trend.Under medial density conditions,the HOAD enzyme sustained a high level,and the utilization capacity of fat body strengthened.Under the condition of 30 larvae/cassette,the energy content and metabolic enzyme activity of M.loreyi were the highest.Under the condition of this density,adults would be induced to migrate,escape from the crowded environment and seek for a new habitat suitable for survival. |
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