| Backgrounds Blattella germanica is a kind of important, globally distributed, urban pest, which is the carrier of bacteria, viruses, and parasite ova, therefore, could transmit many kinds of diseases and bring about much of hazard to public health. With the more and more rapid urbanization, the infestation of Blattella germanica has become more and more seriously, and the infectious ranges have propogated from such special industry facilities as hotels, cafeteria, food processing factories, to the governmental institutions, schools, general institutes, and civil househood; therefore, the Blattella germanica infestation has become a public focused health problem. With their strong adaptation capability, rapid reproduction, and high insecticide resistance level, the Blattella germanica has become the important and difficult to disinfect objectives for the urban pest control and prevention program. Currently, chemical prevention and control is still an important countermeasure for the Blattella germanica, however, not only is the environments contaminated and human health damaged for long-term and frequent usage of chemical insecticides, but also resistance to insecticides such as pyrethroids, organphgosphates developed in Blattella germanica, which has become one of factors constraining chemical prevention and control of this kind of pest.Objectives By the insecticide resistance monitoring and studying of related enzyme activities of different geographic Blattella germanica populations within Shandong Province, present study planned to understood and highlight the insecticide resistance levels and their development trend, to further study the biochemical mechanisms for the development and propogation of the insecticide resistance, thus, to provide the theoretic basis for the implementation of scientifically rational and effective secticide resistance prevention and control strategies, which will be of important theoretic and applicative value to realize the sustainable control of Blattella germanica.Materials and Methods In present study, the field populations of experimental animal Blattella germanica, were collected from seven pest vector monitoring sites within the territory of Shandong Province, i.e. Jinan, Qingdao, Zibo, Tai’an,Dezhou, Dongying, and Jining, respectively. First, it was monitored the levels of resistance to five commonly used health insecticides:beta cypermethrin, deltamethrin, cypermethrin, propoxur, and acephate in seven populations of Blattella germanica collected from different geographic sites, with the cockroach resistance monitoring method recommended by World Health Organization, i.e. insecticide-impregnated filter method; and the laboratory sensitive strains cultured in Pest Vector Institute of Shandong Province Centers for Disease Control and Prevention was used as the reference population. The half Killing Time (KT50), toxicity regression equation and resistant coefficient for each population strain were statistically analyzed, respectively, to comprehensively understand resistance state to common chemical insecticides in the Blattella germanica within the territory of Shandong Province. Next, it was biochemically determined the enzyme activities of acetylcholin esterase (AChE), glutathione S-transferase (GSTs) and hyperoxide mutase (SOD), the protein expression levels of corresponsive enzymes, with SDS-polyacrylamide gel electrophoresis, within different geographic populations of Blattella germanica. By studies on effects of metabolism enzymes and the target enzyme activities of Blattella germanica on its insecticide resistance level, and by assessment of relationship between GSTs, AChE and SOD, and the insecticide resistance level, it could be explored the feasibility of relative activies of these three enzymes as monitoring biomarkers for insecticide resistance in Blattella germanica, the biochemical mechanisms for the development and propogation of these insecticide resistances, and, based on this findings, proposals and recommendations for a practical and feasible prevention and control strategy.Main Results The results of insecticide-impregnated filter method have demonstrated that, among the seven geographic populations of Blattella germanica, the strains generally had high levels of resistant coefficient to cypermethrin (37.99, Zibo strain), and deltamethrin (28.49, Jinan strain), intermediately levels of resistant coefficient to beta cypermethrin (8.42, Jinan strain) and acephate (7.44, Jinan strain), and low levels of resistant coefficient to propoxur (<2, almost any insecticide resistance). Apart from propoxur in which any insecticide resistance developed, different resistance levels to other four kinds of insecticides have been developed within the seven geographic populations of Blattella germanica. Among them, the insecticide resistance for Jinan and Zibo population strains are within intermediately or high level, these for Dezhou, Jining, and Dongying population strains are within low, intermediately or high level, and these for Qingdao, and Tai’an population strains are within low or intermediately level. The enzyme activities and the corresponsive protein expression levels of acetylcholin esterase (AChE), glutathione S-transferase (GSTs) and hyperoxide mutase (SOD) were biochemically determined for the seven geographic populations of Blattella germanica. The relative activities of GSTs and AChE for the seven populations of strains were within101-153and123-346, respectively, which were significantly higher than that for the sensitive reference strains. However, relative activities of SOD for the seven populations of strains were within100-112, and there were any significant difference from the corresponsive sensitive reference strains. The results of protein electrophoresis have shown that the protein content for the field strains of Blattella germanica were significantly higher than that for the corresponsive sensitive reference strains, and the band density for AChE were also slight increased.Conclusions and Suggestions Currently, different resistance levels to common health insecticides have been developed in seven geographic populations of Blattella germanica within Shandong Province, and some obvious district differences have been manifested with resistance levels to the same kind of insecticide. Furthermore, there were some significant differences for the resistance levels to the different kinds of insecticides within the same geographic population of Blattella germanica. The resistance levels for the Jinan and Zibo population strains were highest, followed by the Dezhou, Jining, and Dongying population strains, and resistance levels for the Qingdao and Tai’an population strains were lowest. Among the five commonly used insecticides, the resistance levels to cypermethrin and deltamethrin were highest, followed by beta cypermethrin and acephate, and there were almost any resistance developed to propoxur. The study results have also shown that GSTs and AChE acivities for field populations of Blattella germanica were significantly higher than that in the corresponsive sensitive reference strains, and there were a positive correlation between the relative enzymatic activities and the insecticide resistance levels. All of these suggested that GSTs and AChE may be involved with the insecticide resistance in Blattella germanica, and be closely related with the development and propogation of insecticide resistance. Therefore, the relative activities of GSTs and AChE may be used as a monitoring biomarker for the insecticide resistance in Blattella germanica. On the other hand, the SOD activities for most field population strains were not siginificantly different from that in the corresponsive sensitive reference strains, thus, the potential for relative SOD activities as monitoring biomarker for the insecticide resistance should be further investigated.Based on present survey, it was suggested that, in the monitoring sites of Jinan, Zibo, Jining, and Dongying, the cypermethrin and deltamethrin should be temporarily suspended for usage, the usage for beta cypermethrin and acephate should be decreased, and the usage for propoxur could be continued. In the monitoring site of Qingdao, the usage for deltamethrin should be decreased, and other four insecticides should be alternatively used to control Blattella germanica. In the monitoring site of Tai’an, the usage for acephate should be decreased, and other four insecticides should be alternatively used. In addition, other new chemical insecticides or new formulations of the common insecticides, such as organic fluorine insecticides or cockroach killing gel bait could be selectively used to either for insecticide management, or for the improvement of the prevention effects, and would be an effective procedure for the prevention and control of Blattella germanica. The future prevention and control strategies for German cockroaches in Shandong Province, should be based on the principles of Integrated Pest Management (IPM), to establish a long-term management and control mechanism for German Cockroaches. Based on relevant ecological and social factors, environmental governance, physical control, government support and public participation should be increased, the monitoring of the density, infestation rate, and insecticide resistance for German Cockroach should be enhanced, and the usage of chemical insecticides should be scientifically rational, to reduce and delay the occurrence of insecticide resistance and to limit the vector density of German Cockroach within the threshold for infestation. |
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