Effects Of CO₂ Modified Atmosphere On Anesthesia,Lethality And Enzyme Activity Of Blattella Germanica

The German cockroach is highly adaptive to various environment and is widely distributed worldwide.It not only causes significant economic losses to human,but also carries and transmits a variety of pathogenic bacteria that endanger human health.For many years,control of German cockroach has mainly relied on chemical methods such as residual spraying and baiting.Chemicals agents can volatilize and adhere to the surface of objects,causing contamination of indoor objects and even bringing safety risks by contact exposure.Meanwhile,with the abuse of chemical insecticides,the problem of German cockroach resistance has become increasingly prominent.Modified atmosphere technology has been widely considered and applied because of its merits of being environment-friendly.In this study,the anesthetic and lethal effects of different CO₂ concentrations and different treatment periods on B.germanica were explored.The impacts of temperature on efficacy of modified atmosphere towards German cockroach,the effects of modified atmosphere on German cockroach of different stages,and the physiological responses of German cockroach under modified atmosphere were investigated to provide theoretical references for economical and effective control of B.germanica.The main results are as follows:1.The effects of different CO₂ levels（30%,40%,50%,60%,70%,80%,90%and100%）and exposing durations（1 h,2 h,3 h,4 h,5 h）on the motility and behavioral abilities of B.germanica during the 4 h recovery period was evaluated through limb tremors and crawling ability.After anesthesia with different CO₂ concentrations for different periods,B.germanica was transferred to the normal condition.It was found that during the 4 h observation period,the number of trembling cockroaches generally increased and then decreased,while the number of immobile cockroaches decreased and then increased.Meanwhile,the German cockroach showed impaired locomotion during the 4 h observation period,exhibiting uncoordinated limbs and unstable leg movements.In addition,under the same treatment period,with the increase of CO₂ concentration the time for German cockroach to start crawling,half to crawl and all to crawl gradually extended.These time of cockroaches under 90%CO₂ was the longest.Under the same CO₂ concentration,with the extension of duration exposing to modified atmosphere,the time for cockroaches to start crawling,half to crawl and all to crawl gradually extended.Among which,the time periods to crawl required under 5 h treatment was the longest.After 1 hour of anesthesia treatment,all German cockroaches at all concentrations began to crawl within 1.5 h.In addition,the study showed that the time for cockroaches to start crawling,half to crawl and all to crawl decreased at 100%CO₂ concentration in comparison with that under 90%CO₂ concentration.Results of this study provided a fundamental basis for applying CO₂-modified atmosphere to anesthetize B.germanica in practice.2.The efficiency of modified atmosphere in controlling B.germanica was determined by evaluating the lethal effects of different CO₂ concentrations and treatment periods of the modified atmosphere.The results showed that both CO₂ concentration and treatment duration significantly affected mortality.Moreover,the interactive effects between CO₂ concentration and treatment period on the mortality of German cockroaches were also significant.Compared with other concentrations and treatment periods,the mortality of German cockroaches peaked at 60%CO₂ concentration treated for 4 hours（100%）.The combination of 60%CO₂and 4 h was the most lethal condition to German cockroaches.In addition,with the variation of treatment periods,the mortality of German cockroaches peaked and did not increase after reaching a certain level of CO₂concentration.3.The mortality of B.germanica treated with 40%and 50%CO₂ for 2 hours was measured at four temperatures including 22℃,26℃,30℃,and 34℃.The results showed that the combination of high temperature and modified atmosphere treatment significantly improved the lethal effects on cockroaches.The mortality of B.germanica increased with the increase of temperature.At 40%CO₂ concentration,the mortality rate of cockroaches at 34℃was 96.67%,being the highest mortality rate among treatments.At 50%CO₂concentration,the mortality rate of cockroaches at 30℃was 92.22%,and no significant difference was found compared with that at 34℃（p>0.05）.Therefore,40%-34℃and50%-30℃were the most effective conditions for controlling B.germanica.4.The male adult,female adult,and nymph of B.germanica were exposed to 40%or 50%CO₂,and the mortality after 2 hours was measured.Results showed that B.germanica was sensitive to the modified atmosphere at all stages.The females were the most sensitive to modified atmosphere,followed by 1-2 nymph,3-4 nymph and 5-6nymph.In contrast,the males were the least sensitive.With the development of nymph,the tolerance of nymphs to modified atmosphere gradually increased.Female and 1-2nymph were the most sensitive to modified atmosphere environment,while male B.germanica adults were the most tolerant,which could be used as an indicator of the effectiveness of modified atmosphere.5.Trehalose content,superoxide dismutase activity,catalase activity,and glutathione-S-transferase activity in B.germanica were measured at different CO₂concentrations and treatment periods.Results showed that the trehalose content gradually decreased with the increase of CO₂ concentration,reaching a minimum of 0.72 mg/g at80%CO₂ concentration,indicating that the trehalose utilization rate gradually increased with the increase of CO₂ concentration.The trehalose content generally decreased and then increased with the extension of the treatment periods.Under short-term stress of the modified atmosphere,B.germanica resisted adverse environments by transforming trehalose.After long-term stress of modified atmosphere,the lethal effects were induced,resulting in a higher trehalose content than in the short-term stress.The activity of SOD and POD increased initially and then decreased with the increase of CO₂ concentration and the extension of treatment period,and the SOD activity in German cockroaches under modified atmosphere was significantly lower than that of control.At low CO₂concentration,the activities of SOD,POD,and GSTs increased with the increase in CO₂concentration,as responses to the increasing content of free radicals in insects.However,at high CO₂ concentration,the body was damaged and the activities of SOD,POD,and GSTs decreased.Elevated CO₂ or prolonged treatment period changed the activities of protective enzymes and detoxification enzymes in German cockroaches,which in turn affected their detoxification ability.The accumulation of toxic substances and the depletion of energy substances ultimately lead to German cockroaches’deaths.