Studies On Specific Activity Of Carboxylesterase And Acetylcholinesterase Of Cigarette Beetle Lasioderma Serricorne (Fabrcius) (Coleoptera: Anobiidae)

The cigarette beetle Lasioderma serricorne(Fabrcius)(Coleoptera:Anobiidae),is the most important stored-tobacco pest in the world.Carboxylesterase(CarE) and Acetylcholinesterase (ACHE) are enzymes mostly related to effects of insecticide and CO₂ against the beetle.Studies on the specific activities of both enzymes were conducted using different stages of the beetle and under conditions of controlled atmosphere with CO₂ or phosphine.The affects of CarE concentration,substrate(a-NA) concentration,pH of the reaction system, the reaction temperature and the reaction time on assaying of the specific activity of CarE in the adults of L.serricorne were studied by orthogonal matrix methods.L₂₅(5⁶) orthogonal matrix was adopted without considering interaction.The results revealed that the 5 factors affected remarkably (p＜0.01) on the activity of CarE of the adults of L.serricorne,and were in the order of temperature＞pH＞time＞concentration of the substrate＞concentration of CarE.The optimal conditions for assaying the activity of CarE in the adult beetles,through range analysis,analysis of variance and multiple comparison,were considered as 1 beetle/mL,5.0×10^-4 mol/L substrate,pH 7.5,42℃,and 10 minutes.Body distribution and subcellular distribution of CarE and AChE from L.serricorne were investigated.The percentages of CarE specific activity in the head,thorax and abdomen were 49.7%,32.51%and 17.79%of total activity in the adult,while 33.03%,35.83%and 31.14%in the mature larvae.The ACHE in the head had the highest specific activity,which evaluated 79.4%in the adult and 79.48%in the mature larvae.There was a significant difference(p＜0.01) in the distribution percentages of AChE in head from thorax and abdomen.With differential centrifugation,subcelhlar distributions of CarE and AChE from head,thorax and abdomen of adult and mature larvae were studied.The results showed that the major portion of CarE located in the supernatant,while minor in cell nucleus and cell debris,and much lesser in the mitochondrion and the microsome.The major portion of the total AChE was member-bound(above 90%in mitochondria,mitochondrion and nucleus and cell debris) and associated primarily with mitochondria.The specific activity of CarE and AChE in different stages and instars of L.serricorne were studied.The results showed that the specific activity was different at different stages and instars of the beetle.The CarE specific activity of the mature larvae was the highest and that of the pupa lowest.The order of the CarE specific activity was mature larvae＞2nd-instar larvae＞adult＞pupa. The order of the ACHE specific activity was 2nd-instar larvae＞adult＞mature larvae＞pupa.With different period exposed in phosphine and airing,the effect of phosphine on the CarE and AChE specific activity of L.serricorne were studied.The results showed that the CarE specific activity increased in the adults exposed in phosphine.This suggested that the CarE has detoxification for phosphine.The AChE specific activity was inhibited when the adults were exposed in phosphine,and it decreased within certain period of airing but then increased in further period.The acute lethal effects of CO₂-controlled atmosphere(CO₂-CA) on the adults of L. serricorne were studied.The results showed that the mortality of the adults increased,with increasing of exposure time,and the half lethal time decreased with increase of CO₂ concentration. The effect of CO₂ on the CarE and AChE specific activity were studied with the different CO₂ concentration,fixed exposure time or in constant CO₂ concentration,and different exposure time. The results showed that the CarE specific activity of the adults under CO₂- CA.The AChE specific activity of the adults was inhibited in higher CO₂ concentration CA.When the adults were exposed for a longer time in the higher CO₂ concentration under CA,the CarE specific activity from the survival adults increased and the AChE specific activity increased.These suggested that the CO₂-CA could enhance activity of CarE and depress the activity of AChE.