| The rice stem borer,Chilo suppressalis Walker,is an economically important pest distributed in the rice producing regions of all over the world.The intermittently explosive situation of the rice stem borer,which has been appeared since 1990s,is significantly correlative with cold hardiness of overwintering larvae which determine its initial population numbers in the next year.Induced responses on some cold-resis-tant substances in the larvae by artificially control temperature in the laboratory was researched systematically in the present study.Effects of rapid cold hardening(RCH) on the cold tolerance of the diapause larvae in the laboratory were primarily discussed.The results show as follow:1.When the diapause larvae of the rice stem borer were exposed to series temperatures and gradient temperatures(from 28℃to-14℃),the results presented a gradient decline,but both treatments showed no significant difference at 0.05 level.The contents of lipid in the larvae by two treatments presented no significant difference at 0.05 level.When the non-diapause larvae of the rice stem borer were exposed to series temperatures and gradient temperatures,the results of both treatments showed no significant difference excluding those of the larvae which subjected-14℃of the gradient temperatures stress.The contents of lipid in the non-diapause larvae by two treatments presented no significant difference at 0.05 level.The contents of total sugar in the diapause and non-diapause larvae by the series low temperature stress showed no obvious regulation,while the contents of total sugar in the larvae by the gradient low temperature stress presented a gradient decline.Four species of low-molecular carbohydrates,such as trehalose,glucose,glycerol and fructose in the diapause and non-diapause larvae.The results of fructose and those of glycerol showed no significant difference between diapause and non-diapause larvae by both treatments.The results of trehalose and those of glucose increased first and decreased later in the diapause and non-diapause larvae that subjected series low temperature stress.While the results of the trehalose in diapause and non-diapause larvae under gradient low temperature stress increased firstly,decreased secondly and increased later,while that of glucose was in adverse.2.The activities of SOD(Superoxide Dismutase) and POD(Peroxidase) in both diapause and non-diapause larvae by the series low temperature stress were lower than those of SOD and POD in the larvae by the gradient low temperature stress,but that of CAT(Catalase) was in adverse(P＜0.05).3.The discriminating temperature of the diapause larvae of the rice stem borer was about-21℃.Mean survival rates of the larvae which exposed to either 0℃or 5℃for 2h and 4h before expose to the discriminating temperature for 2h were significantly higher than those of the control groups(P＜0.05).Moreover,the highest survival rate appeared in the larvae after 0℃for 4h treatment.The protection against low temperature stress gained by RCH at 0℃for 4h was rapidly lost on return to 28℃for 0.25-1h.Mean survival rates of RCH larvae were significantly higher than those of non-acclimated (NACC) larvae and acclimation(ACC) larvae when they were exposed to the discriminating temperature for 2h or 4h(P＜0.05).Moreover,the rates of NACC,ACC,RCH and ACC+RCH larvae from 2 to 6h to the discriminating temperature resulted in a significantly decline.4.The contents of total lipids,total sugar and low-molecular carbohydrates (trehalose,glucose and glycerol) in the larvae which exposed to 0℃for 4h showed no significant difference at 0.05 level compared to those of the larvae reared at 28℃and those of the larvae-21℃for 4h.But the contents of water in the larvae which exposed to 0℃for 4h were obviously decreased(P＜0.05) compared to those of the larvae reared 28℃.The contents of water in the larvae were no significant difference compared to those of the larvae which directly the discriminating temperature.The SOD activity in the larvae which subjected RCH were obviously decreased compared to those of the control,but were no significant difference compared to those of the larvae which directly were subjected-21℃for 4h.The POD activity in the larvae which subjected RCH were obviously higher than those of the larvae which subjected 28℃and-21℃. The CAT activity in the larvae which subjected RCH were no significant defference compared to those of the larvae which reared 28℃and those of the larvae which subjected-21℃.Therefore,it could be concluded that RCH might enhance cold hardiness and affect partly physilolgical and biochemical components of the diapause larvae of the rice stem borer,but the underlying physiological mechanisms needs to be further explored.
|
PDF Full Text Request