Occurrence Regularity and Life History of Cigarette Beetle Lasioderrma serricorne (Fabricius) in Tobacco Leaf Threshing and Redrying Workshop

Ding CHEN, Yingjie JIANG, Zijun ZHAO, Chaojun LUO, Xingling WANG, Jie XIE, Pengchao CHEN, Fei XU, Yongan REN, Lin LU, Xueqin ZHANG, Shunxian LIANG

1. China Tobacco Guizhou Import and Export Co., Ltd., Guiyang 550003, China; 2. Guizhou Light Industrial Technical College, Guiyang 550025, China; 3. Guizhou Tobacco Redrying Co., Ltd. Guiyang Redrying Factory, Guiyang 550005, China; 4. Guiyang Customs of the People’s Republic of China, Guiyang 550000, China

Abstract [Objectives] The paper was to study the occurrence regularity and life history of cigarette beetle Lasioderrma serricorne (Fabricius) in tobacco leaf threshing and redrying workshop. [Methods] With the tobacco leaf threshing and redrying workshop as the survey site, the occurrence regularity of L. serricorne was investigated, and the life history table was inferred according to its biological characteristics. The temperature, humidity and duration of tobacco leaf threshing and redrying were simulated in the laboratory to study the survival rate of all states of L. serricorne in this environment. [Results] The lifecycle of L. serricorne in tobacco leaf threshing and redrying workshop was: the overwintering generation pupated in late February; the pupa began to emerge in early March, and reached its peak in late March. The first-generation eggs started hatching in late March, pupated in late May, emerged in early June, and reached the peak eclosion of the first-generation adults in mid-July. The second-generation eggs began to hatch in late July, pupated in mid-August, emerged in late August, and reached the peak eclosion of the second-generation adults in mid-September. The third-generation eggs began to hatch in mid-September; most of the larvae began to overwinter, some pupated in mid-November and survived the winter as pupae, and some pupae emerged to adults. The survival test results of different states of L. serricorne under simulated temperature, humidity and duration in the tobacco leaf threshing and redrying process showed that the mortality rates of eggs in simulated 1, 2 and 3 conditions were about 51.22%, 90.24% and 100%, and the mortalities of larvae in simulated 1, 2 and 3 conditions were about 18.30%, 81.25% and 100%, respectively. The mortalities of pupae in simulated 1, 2 and 3 conditions were about 69.39%, 100% and 100%, and the mortalities of adults in simulated 1, 2 and 3 conditions were about 100%, 100% and 100%, respectively. [Conclusions] L. serricorne of different states can be killed by appropriately raising the temperature during threshing and redrying.

Key words Cigarette beetle; Lifecycle; Tobacco leaf threshing and redrying workshop; Mortality rate; Regularity

1 Introduction

Tobacco is currently an economic crop in the world. It has been widely planted in Asia, Africa, North and South America, Europe and other places[1]. However, the stored tobacco needs to be stored in warehouse for 2-3 years, so it is deeply harmed by tobacco beetleLasioderrmaserricorne(Fabricius). The damage ofL.serricornewill lead to leaf holes, decreased filament formation rate and reduced quality of tobacco[2]. The loss is about 6.5 billion yuan in China[3], and is about 300 million USD per year throughout the world[4]. In addition to harming tobacco leaves,L.serricornealso harms cigarettes, chocolate, flour, grains, peppers, medicinal materials,etc.[5]. To achieve accurate prevention and treatment ofL.serricorne, it is necessary to understand its occurrence pattern and life history, but because of the difference in temperature and food, there will be differences in the number of generations of annual occurrence, which is generally 3-6 generations per year, and as many as 7 generations in areas with higher temperatures, or as few as 1-2 generations in areas with lower temperature[6]. For example, there are 3 generations in Hubei and Nanchang, 2 generations in Shanghai, 2-3 generations in Anhui and Guiyang, and 3-4 generations in Fujian every year[7-10]. Although the generations and life history ofL.serricornein Guiyang area every year are known[8], the ambient temperature will rise when the threshing and redrying workshop is turned on. The occurrence regularity and life history ofL.serricornein the workshop will be different from the external environment. In this study, the occurrence regularity ofL.serricorneadults in tobacco leaf threshing and redrying workshop was investigated, and their life history was inferred based on the biological characteristics studied by Wangetal.[11]. When the temperature is higher than 60 ℃ for 3 min, higher than 70 ℃ for 2 min, or higher than 55 ℃ for 4 min,L.serricorneof different states will be killed[12]. When the warehouse temperature is kept at 50-60 ℃ for 24-36 h[13], at 50 ℃ for 166 min or at 54 ℃ for 38 min, mostL.serricornecan be killed[14]. However, the survival status ofL.serricornein tobacco leaf threshing and redrying process under different conditions of temperature, humidity and duration had not been studied, so experiments were carried out to provide data support for the prevention and control ofL.serricornein tobacco leaf threshing and redrying workshop.

2 Materials and methods

2.1 Pest monitoring

2.1.1Time. The test was conducted from January 2021 to December 2021.

2.1.2Arrangement. The tobacco leaf threshing and redrying workshop surveyed is shown in Fig.1.

Fig.1 Schematic diagram of Lasioderrma serricorne monitoring points

2.1.3Materials. Tobacco beetle sexual attractant was produced by Wuhan Dongchang Storage Technology Co., Ltd.

2.1.4Location. The tobacco leaf threshing and redrying workshop surveyed is located in Guiyang, Guizhou, where the annual average temperature is 15.3 ℃ and the average summer temperature is 23.2 ℃. Guizhou Tobacco Redrying Co., Ltd. Guiyang Redrying Factory has an annual tobacco import and export volume of about 32 000 t, and maintains 25 000 t of tobacco throughout the year (including 20 000 t leased). The tobacco factory covers an area of about 730 000 m2, and the tobacco leaf threshing and redrying workshop is 12 000 m2.

2.1.5Investigation method. From January 2021, the tobacco beetle sexual attractant had been placed at different points according to the instructions (Fig.1), and the number ofL.serricornetrapped by tobacco beetle sexual attractant was counted daily until December 2021. According to the biological characteristics studied by Wangetal.[11], the life history ofL.serricornewas inferred.

2.2 Simulated survival experiment

2.2.1Instruments. Artificial climate box (LAC-450HPY-2, Shanghai Yuelong Co., Ltd.), electric heating blast drying box (Type 101-1AB, Tianjin Test Instrument Co., Ltd.).

2.2.2L.serricornefeeding. 200 g of feed (corn∶smoke foam∶brewer’s yeast = 9∶5∶5) were put in a 350 mL can, and placed in an electric heating blast drying box at 70 ℃ for 4 h. Afterwards, they were placed under the rearing conditions of temperature 33 ℃, relative humidity (75±5)%, light 10D: 14L.

2.2.3Test method. According to the leaf tobacco-threshing and redrying-technical specification inTobaccoIndustryStandardofthePeople’sRepublicofChina(YC/T 146-2010), the conditions of humidity 70% and 90% were simulated by artificial climate box, and the humidity of 0 was simulated by electric heating blast drying box. Each simulation was a complete process, and the repetition of the process needed to go through all the conditions, namely 1 min at 50 ℃, 90% humidity, 3 min at 27 ℃, 10% humidity, until all processes were completed. The number of hatching and eclosion was observed, respectively. Different insect states ofL.serricornewere tested according to the simulated conditions. After the test, they were put back to the feeding conditions to continue feeding, and the number of deaths was checked after 48 h.

2.3 Data analysis

Mortality rate (%)=( Number of dead insects/Number of test insects)×100;

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

All data were analyzed byLSDsignificant difference test in SPSS version 23 software (IBM, NY, United States).P<0.05 indicated significant difference.

3 Results and analysis

3.1 Pest monitoringL.serricornewas first detected in the tobacco leaf threshing and redrying workshop in early March, and the peak period ofL.serricorneadults occurred in late March, late April, June, late July, August, early September, and late September. The highest number ofL.serricornewas trapped from late July to early September, and the number ofL.serricornedropped sharply after early September, but there were stillL.serricorneadults occasionally trapped.

3.2 Life history tableThe overwintering generation pupated in late February, began to emerge in early March, and reached the peak of overwintering generation in late March. The eggs of the first generation started to hatch in late March, pupated in late May, and began to emerge in early June. In mid-July, the first-generation adults reached the eclosion peak. The eggs of the second generation began to hatch in late July, pupated in mid-August and emerged in late-August, and the eclosion peak of the second-generation adults appeared in mid-September. The eggs of the third generation began to hatch in mid-September; most of the larvae began to overwinter, and some pupated in mid-November and overwintered as pupae (Table 1).

3.3 Simulated survival experimentThe mortality rates of eggs in simulated 1, 2 and 3 conditions were about 51.22%, 90.24% and 100%, and the mortality rates of larvae in simulated 1, 2 and 3 conditions were about 18.30%, 81.25% and 100%, respectively. The mortalities of pupae in simulated 1, 2 and 3 conditions were about 69.39%, 100% and 100%, and the mortalities of adults in simulated 1, 2 and 3 conditions were about 100%, 100% and 100%, respectively. TheLSDtest results of SPSS showed that the mortality of eggs, larvae and pupae in simulated 2 and 3 conditions were not significantly different, and the mortality differences between simulated 1, 2 and 3 conditions were significant. There was no significant difference between adults under the three simulated conditions of temperature, humidity and duration (Table 2).

Table 1 Life history table of Lasioderrma serricorne in the tobacco leaf threshing and redrying workshop of Guizhou Tobacco Redrying Co., Ltd. Guiyang Redrying Factory

Table 2 Corrected mortality of Lasioderrma serricorne of different states in the simulated situation of tobacco leaf threshing and redrying

4 Conclusions and discussion

In this study, it was found that in late March, late April, June, late July, August, early September, and late September in the tobacco leaf threshing and redrying workshop,L.serricornebroke out during the peak period ofL.serricorneadults. According to the occurrence law and the biological characteristics, the life history table ofL.serricornewas deduced (Table 1). The survival experiment ofL.serricornein such environment was studied by simulating the temperature, humidity and duration of tobacco leaf threshing and redrying process. It was found that almost all insect states died under simulated 3 condition; the mortalities of eggs, larvae and pupae under simulated 2 condition respectively were 90.24% and 81.25%, and the mortality of pupae and adults reached 100%. Under simulated 1 condition, the mortality of adults was 100%, and the mortalities of eggs, larvae, and pupae were 51.22%, 18.30% and 69.39%, respectively.

After investigation, it was found thatL.serricorneadults appeared in the first ten days of March, probably because the operation of machine in the tobacco leaf threshing and redrying workshop raised the ambient temperature, which was different from the external environment. Therefore, the life history ofL.serricornein the tobacco leaf threshing and redrying workshop is inconsistent with that reported by Chenetal.[15]: theL.serricornehad 3 generations per year in warehouses in Guiyang and other places, which pupated in April, and entered the outbreak period of overwintering adults in early May, the peak emergence period in late May, and the first generation period of adults in mid-July. During the period from late September to early October, the second generation of adults broke out. In mid-March, the larvae ofL.serricornein Fujian began to survive the winter[6].

In this study, it was found that pupation started in late February; the overwintering generation reached the peak period in late March; the first generation of adults reached the peak period in mid-July; and the second generation of adults reached the peak period in mid-September. Except for the first generation, which was 2 months earlier than the previous study, the rest were more than half a month earlier[6, 15-16]. Therefore, in the actual prevention and control, the prevention and control procedures should be adjusted in combination with this study to achieve a better prevention and control effect. In addition, the survival experiment ofL.serricornein the simulated temperature and humidity in tobacco leaf threshing and redrying process shows that the appropriate temperature increase in such environment is conducive to the prevention and control ofL.serricorne, and other control methods can be combined to reduce the loss of tobacco.