Study on Toxicity of 9 Biocontrol Microbial Products to Adult Population of Tobacco Beetle, Lasioderrma serricorne (Fabricius)

Zijun ZHAO, Yingjie JIANG, Ang LI, Chaojun LUO, Pengchao CHEN, Xueqin ZHANG, Ling LU, Yongan REN, Fei XU, Shunxian LIANG

1. China Tobacco Guizhou Import and Export Co., Ltd., Guiyang 540003, China; 2. Guizhou Light Industry Technical College, Guiyang 550032, China; 3. Guiyang Redrying Factory, Guizhou Tobacco Redrying Co., Ltd., Guiyang 550005, China

Abstract [Objectives] The paper was to study the toxicity of 9 biocontrol microbial products to adult population of Lasioderrma serricorne. [Methods] Nine biocontrol microbes were used as test materials to study their toxicity to the experimental population of L. serricorne adults. [Results] The toxicities of these biocontrol microbes from low to high at 5 d post spraying were: Luhai Beauveria bassiana powder (LC50=462.752×108 spores/L), Meichongzhi B. bassiana powder (LC50=9 713.157×108 spores/L), Yiqiang Bio B. bassiana powder (LC50=11 203.321×108 spores/L), Nongbao Bio B. bassiana powder (LC50=12 188.866×108 spores /L), Yeshengwang B. bassiana powder (LC50=21 685.532×108 spores /L); Fatu Bacillus thuringiensis suspension (LC50=1.084 4×108 IU/L), Laojite B. thuringiensis suspension (LC50=2.056×108 IU/L), Lujinwa B. thuringiensis powder (LC50=2.273×108 IU/L), Nongbao Bio B. thuringiensis powder (LC50=18.399×108 spores /L). The toxicities of these biocontrol microbes from low to high at 10 d post spraying were: Nongbao Bio B. bassiana powder (LC50=0.072×108 spores /L), Yiqiang Bio B. bassiana powder (LC50=2.484×108 spores /L), Luhai B. bassiana powder (LC50=44.551×108 spores/L), Meichongzhi B. bassiana powder (LC50=96.447×108 spores/L), Yeshengwang B. bassiana powder (LC50=723.347×108 spores/L); Lujinwa B. thuringiensis powder (LC50=0.000 1×108 IU/L), Fatu B. thuringiensis suspension (LC50=0.045×108 IU/L), Laojite B. thuringiensis suspension (LC50=0.064 4×108 IU/L), Nongbao Bio B. thuringiensis powder (LC50=1.899×108 spores/L). The toxicities of these biocontrol microbes from low to high at 15 d post spraying were: Meichongzhi B. bassiana powder (LC50=0.001×108 spores/L), Nongbao Bio B. bassiana powder (LC50=0.01×108 spores/L), Yiqiang Bio B. bassiana powder (LC50=0.084×108 spores/L), Luhai B. bassiana powder (LC50=2.370×108 spores/L), Yeshengwang B. bassiana powder (LC50=8.915×108 spores/L); Lujinwa B. thuringiensis powder (LC50=0.16×104 IU/L), Laojite B. thuringiensis suspension (LC50=0.185×104 IU/L), Fatu B. thuringiensis suspension (LC50=32.211×104 IU/L), Nongbao Bio B. thuringiensis powder (LC50=1 590×104 spores/L). [Conclusions] According to the three stages of tube rubbing, it is found that the control effects of Lujinwa B. thuringiensis powder and Meichongzhi B. bassiana powder are the best, and the results will provide technical support for the biological control of L. serricorne adults.

Key words Tobacco beetle; Biocontrol; Microbial products; Virulence; Toxicity; LC50

1 Introduction

Tobacco is now an important raw material for economic products all over the world, bringing huge economic benefits to many countries.Lasioderrmaserricorneis a main pest that cause losses during tobacco storage[1-3]. Every year in China and the world, tobacco’s storage and products are harmed byL.serricorne[4-5]. At present, physical control, chemical control and biological control are the major control methods againstL.serricorne[6]. Physical control mainly includes methods such as temperature control and transmission blocking[6-10], while chemical control is mainly composed of fumigation, pesticide and other methods[11-14]. However, they all have their own shortcomings. Physical control methods rely on the airtightness of warehouses or just block the spread ofL.serricorne. Chemical control methods inevitably lead to drug resistance, which has been proved by many reports[13,15-16]. However, there is another method that can achieve the harmonious development of man and nature, namely biological control.

After the study by Liuetal.[17], it was found that amongPaecilomycesfumosoroseus(Wize) Brown & Smith,P.catenannulatusLiang,P.cateniobliquusLiang andBeauveriabrongniartii(Sac) Petch,B.bassiana(Balsamo) Vuilemi and other fungi,B.bassianahas the highest infection fatality rate forL.serricorne. And the current studies onB.bassianaalso demonstrate that Bb050722[18], GUIFR-GL-5[19], GZUIFR-GL5-08i[20]and other strains are effective againstL.serricorne. In addition,Bacillusthuringiensishas good infection and lethal effect onL.serricorne. Gao[21]isolated 9 strains ofB.thuringiensiswith high killing rate onL.serricornefrom re-cured tobacco leaves. Qietal.[22]found that 18 strains ofB.thuringiensiswere effective againstL.serricornelarvae with high biological activity. Huetal.[23]found that GXZY032 strain ofB.thuringiensishas high insecticidal rate toL.serricornelarvae. At present, although many biocontrol bacteria have been found to have good infection and lethal effect onL.serricorneadults, there are no biocontrol products widely used in the field ofL.serricorneadults control, and the comparative study of related products in the control ofL.serricorneadults outdoors and indoors is still blank. Therefore, in this study, 9 biocontrol microbes were used as test materials to study their toxicity to the experimental population ofL.serricorneadults, in order to provide technical support for the biological control ofL.serricorneadults.

2 Materials and methods

2.1 Insects collection and breedingTobacco beetle (L.serricorne) adults were collected from Guiyang Redrying Factory, Guizhou Tobacco Redrying Co., Ltd., and were reared and purified for at least 5 generations in the laboratory of Guizhou Engineering Research Center for Mountain Featured Fruits and Products of Guizhou Light Industry Technical College. 200 g of feed was composed of corn, smoke foam and brewer’s yeast at the ratio of 9∶5∶5, andL.serricornewere grown under the conditions of temperature (33±1) ℃, relative humidity (75±5) %, and light 10 D∶14 L.

2.2 Experimental equipment and materialsExperimental equipment: artificial climate box (LAC-450HPY-2, Shanghai Yuelong Co., Ltd.).

B.bassiana: LuhaiB.bassianapowder (Shanxi Luhai Pesticide Science Technology Co., Ltd.), Nongbao BioB.bassianapowder (Guangxi Nongbao Bioengineering Co., Ltd.), Yiqiang BioB.bassianapowder (Beihai Yiqiang Biotechnology Co., Ltd.), YeshengwangB.bassianapowder (Beihai Yeshengwang Biotechnology Co., Ltd.), MeichongzhiB.bassianapowder (Guangzhou Duoyuduo Biotechnology Co., Ltd.).

B.thuringiensis: LaojiteB.thuringiensissuspension (Shandong Lukang Biological Pesticide Co., Ltd.), LujinwaB.thuringiensispowder (Fujian Green Shell Bio-Pesticide Co., Ltd.), Nongbao BioB.thuringiensispowder (Guangxi Nongbao Bioengineering Co., Ltd.), FatuB.thuringiensissuspension (Shandong Lushi Pesticide Co., Ltd.).

2.3 MethodsPreparation of medicinal solution (concentration 1): Weigh 10 g or 10 mL of microbial powder or suspension in a beaker, add 90 mL of purified water and dissolve in a watering can to obtain concentration 1.

Preparation of medicinal solutions (concentrations 2, 3, 4, 5): Take 10 mL of the stock solution from the solution of concentration 1 by a pipette and dilute in a watering can by adding 90 mL of pure water to obtain the solution with a concentration gradient of 2. Repeat the previous operation to obtain solutions with concentration gradients of 3, 4, 5, select 20L.serricorneadults and put them into the pudding boxes with 2 cm×2 cm Yunyan 85 tobacco.

Spray method: Refer to the spraying method in part 9 ofGuidelineforLaboratoryBioassayofPesticidesand theAgriculturalIndustryStandardofthePeople’sRepublicofChina(NY/T 1154.9-2008). Formulate the following spraying methods and plan: adjust the size of the spray mouth of the watering can, spray 2-3 times at the side of the pool, open the pudding box withL.serricorneadults, and spray the mouth of the watering can 30-40 cm away from the pudding box twice; 3 repetitions. At 5, 10, and 15 d post spraying, observe and record once (mainly observe the number of deaths ofL.serricorneadults).

2.4 Data analysisMortality rate (%)=(Number of dead insects/Number of test insects)×100;

Corrected mortality rate (%)=(Mortality rate in experimental group-Mortality rate in control group)/(1-Mortality rate in control group)×100.

Preliminary data processing was performed in Microsoft Excel (version 2016), and then the toxicity regression equation andLC50were obtained through Probit model simulation of SPSS (version 23).

3 Results and analysis

3.1B.bassianaproducts againstL.serricorneBy studying the toxicity infection test of 5 products ofB.bassianaagainstL.serricorneadults, the toxicity regression equations andLC50were obtained (Table 1), and theirLC50at 5 d post spraying successively were (from low to high, the same below): LuhaiB.bassianapowder, MeichongzhiB.bassianapowder, Yiqiang BioB.bassianapowder, Nongbao BioB.bassianapowder, YeshengwangB.bassianapowder. The difference between the best (462.752×108spores/L) and the worst (21 685.532×108spores/L)LC50was about 47 times.

TheLC50at 10 d post spraying successively were: Nongbao BioB.bassianapowder, Yiqiang BioB.bassianapowder, LuhaiB.bassianapowder, MeichongzhiB.bassianapowder, YeshengwangB.bassianapowder. The difference between the best (0.072×108spores/L) and the worst (723.347×108spores/L)LC50was about 10 041 times.

TheLC50at 15 d post spraying successively were: MeichongzhiB.bassianapowder, Nongbao BioB.bassianapowder, Yiqiang BioB.bassianapowder, LuhaiB.bassianapowder, YeshengwangB.bassianapowder. The difference between the best (0.001×108spores/L) and the worst (8.915×108spores/L)LC50was about 8 915 times.

From the above, it can be seen that MeichongzhiB.bassianapowder had a good control effect onL.serricorneadults. In addition, it was found in the experiment that with the extension of time, the effect of biocontrol fungi was getting better and better, but theLC50gap between the best and the worst products was the largest at 10 d post spraying and the lowest at 5 d post spraying. So when studying the effect of other biocontrol products on insects, more observation time should be set as far as possible.

3.2B.thuringiensisproducts againstL.serricorneThe toxicity regression equation andLC50shown in Table 2 are the results of the control study ofB.thuringiensisagainstL.serricorneadults. TheLC50at 5 d post spraying successively were (The units of Nongbao BioB.thuringiensispowder are different from other product units, and the comparison here is based on their equal units; the same below): FatuB.thuringiensissuspension, LaojiteB.thuringiensissuspension, LujinwaB.thuringiensispowder, Nongbao BioB.thuringiensispowder. The difference between the best (1.084 4×108IU/L) and the worst (18.399×108spores/L)LC50was about 17 times.

Table 2 Toxicity regression equation and LC50 of Bacillus thuringiensis products against Lasioderrma serricorne adults

TheLC50at 10 d post spraying successively were: LujinwaB.thuringiensispowder, FatuB.thuringiensissuspension, LaojiteB.thuringiensissuspension, Nongbao BioB.thuringiensispowder. The difference between the best (0.000 1×108IU/L) and the worst (1.899×108spores/L)LC50was about 18 990 times.

TheLC50at 15 d post spraying successively were: LujinwaB.thuringiensispowder, LaojiteB.thuringiensissuspension, FatuB.thuringiensissuspension, Nongbao BioB.thuringiensispowder. The difference between the best (0.16×104IU/L) and the worst (1 590×104spores/L)LC50was about 9 937 times.

From the above, it can be seen that LujinwaB.thuringiensispowder had control good effect onL.serricorneadults. From the study on the control ofL.serricornebyB.thuringiensis, it was found that the difference between the bestLC50and the worstLC50was still the largest at 10 d post spraying and the smallest at 5 d post spraying.

4 Conclusions and discussion

The study found that LuhaiB.bassianapowder and FatuB.thuringiensissuspension had the best control effect onL.serricorneadults at 5 d post spraying. Nongbao BioB.bassianapowder and LujinwaB.thuringiensispowder had the best effect onL.serricorneadults at 10 d post spraying. MeichongzhiB.bassianapowder and LujinwaB.thuringiensispowder had the best effect onL.serricorneadults at 15 d post spraying.

Besides, the number of viable bacteria, auxiliaries, preparation methods and storage conditions, as well as field environmental factors will have greater impact on the control effect of biocontrol fungicides[24]. And there are many types of biocontrol microbial products, mainly including powders, wettable powders, granules, water dispersible granules and suspensions,etc.[25]. Therefore, different biocontrol products have different control effects onL.serricorneadults, and it is of great significance to study the control effect of different biocontrol products onL.serricorneadults. However, in outdoor prevention and control, it is necessary to adapt to local conditions to achieve the best results.

Acknowledgement

Sincere thanks go to Jinyu ZHAO, Yao LIU, Jing PENG and Jian TANG from Guizhou Engineering Research Center for Mountain Featured Fruits and Products of Guizhou Light Industry Technical College for their help in the research.