Effects of Different Rootstocks on Plant Growth and Fruit Quality of Watermelon

Jiali MENG Shaojun WU Xiawen WANG Xiang YU Ruoyong JIANG

AbstractThe Spodoptera litura occurrence quantity in Tianlong Town, Pingba County, Anshun City was dynamically monitored by an insect sex pheromone electronic measurement and forecast system in 2015 and 2016 and the trapped effect of S. litura was studied by the homemade S. litura sex pheromone traps in Baishiyan Town, Ziyun County and Tianlong Town, Pingba County in 2016 to accurately grasp the occurrence regularity of S. litura and apply insect sex pheromone for controlling S. litura in Central Guizhou tobaccogrowing region. There are 5 generations of S. litura in a year in Central Guizhou region. The first generation of S. litura occurs from late April to middle May, the second from middletolate July to middletolate August, the third from earlytomiddle August to the end of September, the fourth is in the end of October and the fifth in the end of November. S. litura emigrates or enters into the overwintering stage in December. S. litura is almost in active in the daytime during the peak occurrence period of S. litura adults. The first mating time of S. litura is at 17: 30 and its peak mating time is about 22:00. The second mating time of S. litura is at 1: 00-5: 00 and its peak mating time is about 2:30. The trapped S. litura quantity presents an obvious layerbelt distribution that the number in the outer ring is significantly higher than that in the middle ring, and the number in the middle ring is significantly higher than that in the inner ring. The number of trapped S. litura is higher around the outer ring of the testing field and at the draught position than in the lowlying land and inner flat ground.

Key wordsTobacco; Spodoptera litura; Occurrence regularity; Sex pheromone; Central Guizhou

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Received: September 23, 2018Accepted: December 10, 2018

Supported by the Science and Technology Project of Guizhou Tobacco Company, China (201510).

Chengping FAN (1980-), male, P. R. China, agronomist, devoted to research about tobacco planting, Email: 1505930164@qq.com.

*Corresponding author. Rui ZUO (1964-), male, P. R. China, senior experimentalist, devoted to research about tobacco pests and disease, Email: zuorui09@163.com.

Spodoptera litura Fabricius is a nocturnal moth in the Noctuidae family. S. litura is one of the main tobacco pests, and it is distributed in the main producing areas of fluecured tobacco in China. The moth has strong elusiveness, sudden outbreak, multiple occurrences in drought with high temperature in summer and autumn as well as omnivory and feeding preference［1］. S. litura parasitize the plants through the larvaes vigorous eating patterns, oftentimes leaving the leaves completely destroyed. At the beginning, the larvae mainly do damage to the middle and lower leaves of tobacco plants, and as the instars of the moths increases, they begin to move upward to the upper leaves, seriously affecting the yield and quality of fluecured tobacco production. The control of S. litura is still dominated by chemical control, and the larvae of S. litura are the pests in the harvesting period of fluecured tobacco. Therefore, the use of chemical pesticides for control can directly lead to pesticide residues exceeding the standard in tobacco leaves. Since S. litura has multiple reproductive generations and large occurrence amount, the longterm abuse of pesticides can make it generate drug resistance［2-4］, thus increasing the difficulty of control.

Insect sex pheromones are characterized by high biological activity and strong specificity. After the application of pheromones, pests do not produce drug resistance, and pheromones are harmless to their natural enemies, thereby decreasing the amount of applied pesticides, reducing environmental pollution and pesticide residues in agricultural products. Moreover, pheromones are simple to use and the control cost is low. Therefore, the use of insect sex pheromones has important significances for tobacco safety and environmental protection［5］. Insect sex pheromones can not only control the population of S. litura, but also monitor the dynamics of pest population growth and development, and carry out forecasting and prediction［6］. At present, there are few reports on the occurrence and activity of S. litura in Guizhou. Therefore, in this paper, insect sex pheromone electronic monitoring and forecasting system was used to study the occurrence and activity of S. litura in Guizhou Province, in order to understand the occurrence and prevalence rules of S. litura in the tobacco producing areas in central Guizhou Province. In the meantime, the trapping effects of the sex pheromones (selfmade lure) were evaluated scientifically to reduce the use of chemical pesticides, decrease the pesticide residual amount on tobacco leaves and protect the ecological environment of tobacco areas, so as to provide technical supports for the sustainable development of tobacco.

Materials and Methods

Materials

The test materials included the field sex pheromone electronic monitoring and forecasting system for S. litura (SHWNMT of Ningbo Newcom Biotechnology Co., Ltd.), the S. litura traps, which were of generalpurpose type for Noctuidae moths, and the sex pheromone lures for S. litura was of capillary type, which was made by the Institute of Biotechnology, Guizhou Academy of Agricultural Sciences.

Investigation on occurrence quantity of S. litura

The investigation was conducted in the tobacco planting areas of Tianlong Town, Pingba District, Anshun City. During the occurrence of S. litura in 2015-2016, the field sex pheromone electronic monitoring and forecasting was used to monitor the changes in the number of S. litura in real time, so as to understand its occurrence regularity. The total number of S. litura was investigated at different times of a day during the peak occurrence period, so as to understand the daily activities of S. litura.

Pheromone field trapping S. litura

The tests of pheromone field trapping S. litura was conducted in 2016 in Baishiyan Town of Ziyun County and Tianlong Town of Pingba District. Baishiyan Town of Ziyun County had a test tobaccoplanting area of 3 hm2, with the landform of an elliptical shape (4 sides surrounded by mountains); Tianlong Town of Pingba District had a test tobaccoplanting area of 3.33 hm2, with flat landform. The selfmade sex pheromone lures for S. litura were loaded to the generalpurpose traps for moths (cylinder type), and then the traps were fixed to wooden poles or bamboos of 2.0-2.2 m high, which were inserted into the soil. The traps were fixed at least 1.6 m above the ground with intervals of 40 m between each other. For each site, 1 trap was installed, and there were a total of 26 trap sites. The traps were placed in the outer rings of the test sites as well as at the draught positions, in the lowlying zones of the inner rings of the test area and in the flat area inside the test site. During the test period, the trapped number of S. litura was investigated and recorded every 5 d, and the lures were changed every month. DPS and Excel were used to carry out statistical analysis to the data.

Results and Analysis

Occurrence regularity of S. litura

2015

As shown in Fig. 1, on March 31, 2015, the first field trap caught 11 S. litura, indicating that S. litura began to emerge in late March. Only a small amount of S. litura was caught before April 26, indicating that the moth was still in the early stages of emergence. After April 26, the first peak of S. litura of the year appeared, indicating that pupa were gradually emerged into the first generation of adults, and entered the mating period, which lasted until June, and the number of adults was close to 0 in midlate July. The second peak appeared in the midlate August, indicating that the second generation of S. litura appeared and the number was higher than that of the first generation. Then there were another three peaks respectively at the end of September (the third generation), the end of October (the fourth generation) and the end of November (the fifth generation). By the end of November, the number of S. litura was close to 0, indicating that S. litura had emigrated or entered the overwintering stage.



The data from May 26 to July 5 are not recorded because the monitoring system was broken.

Fig. 1Occurrence quantity of S. litura adults in 2015 and 2016

2016According to the investigation results (Fig. 1), the first S. litura was captured on March 15, indicating that S. litura began to emerge in the middle of March. A small amount of S. litura was captured before May 1, indicating that the moth was in the initial stage of emergence, and then the number of S. litura was gradually increased. In the middle of May, the peak of the first generation of S. litura appeared and entered the mating period, and then the number of S. litura followed a gradual decrease. The number was close to 0 from midlate June to early July, indicating that all the first generation S. litura died. Afterwards, the number of S. litura increased gradually, reaching the second peak in middle July. The second generation of S. litura broke out, but the number was lower than that of the first generation, which may be related to excessive rain in July 2016. There were also 3 other peaks of S. litura respectively in early August (the third generation), the end of October (the fourth generation) and the end of November (the fifth generation). At the end of November, the number of S. litura was close to zero, suggesting that S. litura had emigrated or entered the overwintering stage.

Allday activity regularity of S. litura during the peak period

As shown in Fig. 2, S. litura was almost inactive during the day. The active number of S. litura at 9:30-17:30 was close to 0, and after 17:30, the number of active S. litura increased gradually and appeared the first peak at 20:00 and the first bottom at 22:00, indicating that the first activity peak of the male S. litura was 19:30-20:30 with the active number of more than 60. This time period was the first mating peak of S. litura. Afterwards, the number of male S. litura gradually rose after 1:00 in the morning, and reached the peak at 2:30. And then, the number decreased gradually until 7:00, when the active number was close to 0. The results indicated that 1:00-5:00 was the second mating peak for S. litura.

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Fig. 2Quantity of S. litura adults at different time slot in a day

Field trapped amount of S. litura

As shown in Fig. 3, the initial population number of S. litura in Tianlong test area of Pingba District was significantly higher than that in Baishiyan test area of Ziyun Town. There were great differences in the number of trapped S. litura in the traps installed at different places. The trapped number of S. litura presented an obvious layerbelt distribution from the outside to the inside. The number of trapped S. litura was significantly higher in the outer ring than that in the central ring, which was then significantly higher than the number in the inner ring. The test area in Tianlong Town of Pingba District had flat terrain, and the differences between the different rings were significant. The trapped S. litura in the outer ring was 71.5% higher than that in the central ring on average, while the central ring was 81.89% higher than that in the inner ring on average. The test area in Baishiyan Town of Ziyun County showed significant differences in the terrains. Therefore, the trapped number of S. litura in the outer ring was 116.65% higher than that in the central ring, and the central ring was 78.59% higher than that in the inner ring on average. In addition, the trapped number of S. litura of the traps set up in the outer rings as well as the draught positions were 43.69% higher than the number trapped in the lowlying land and the inside flat ground. There were significant differences in the trapped amount of S. litura at different places in different months. The reason was that the adults were trapped in the outer rings before emigrating inward, resulting in the decrease in the number of adults emigrated to the inner rings.

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Fig. 3Trapped quantity of S. litura adults in field during April-August in Tianlong Town, Pingba County and Baishiyan Town, Ziyun County

Chengping FAN et al. Occurrence Regularity and Sexual Pheromone Trapping Effect of Spodoptera litura in Field in Central Guizhou

Conclusions and Discussion

There are 5 generations of S. litura in a year in Central Guizhou region. The first generation of S. litura occurs from late April to middle May, which begins the emergence from the end of March to early April every year. The first generation lasts for a long time, which may be related to the burying depth in the soil for overwintering. The second appears from middletolate July to middletolate August, and there are some differences in the occurrence period between 2015 and 2016, which might be caused by the rainfall in 2016. The third is from earlytomiddle August to the end of September, the fourth is in the end of October and the fifth in the end of November. S. litura emigrates or enters into the overwintering stage in December. The mating times of S. litura are at 17: 30- 22:00 and 1: 00-5: 00 in the morning, when S. litura was the most active. Therefore, these 2 time periods are the best time for filed light trapping, physical and chemical trapping of adults like fumigation, which can not only save the costs but also increase the insecticidal efficacy.

The number of trapped S. litura in the field is significantly higher in Tianlong test area of Pingba than that in Baishiyan test area of Ziyun, which is caused by the differences in the climatic conditions and the population quantity of S. litura. There is a big gap in the number of trapped S. litura in the traps placed in different positions. The trapped S. litura quantity presents an obvious layerbelt distribution that the number in the outer ring is significantly higher than that in the middle ring, and the number in the middle ring is significantly higher than that in the inner ring. The number of trapped S. litura is on average 43.69% higher in the draught positions of the outer ring than any other trapping sites in the outer ring. There are significant differences in the number of trapped S. litura in different rings in different months. May and August are the 2 peaks for trapping S. litura, which is consistent with the annual occurrence regularity of S. litura.

According to the field trapping effect, the layout and placement of traps should be rationally laid out and placed according to the landform, area, crop type and ecological conditions of the crop planting area. Emphasis should be laid on the layout of traps in the outer ring as well as the draught positions surrounded the target crops by installing 1 sex pheromone trap every 15-20 m, which form a protective circle in the outer ring, so as to reduce the number of S. litura emigrated into the control area. Places of nondraught positions and the central areas should be secondary control area, where 1 sex pheromone trap should be installed at the distance of about 50 cm or so. Since S. litura is a high migratory species, adults can be caught by the traps installed in the trees or buildings at a higher height. In addition, the fluecured tobacco plants are relatively high (generally about 1.5 m in height). If the hanging height of trap is low, the filed permeability becomes poor as the leaf area of the fluecured tobacco plants increases, which is not conducive to the emission of sex pheromones, resulting in poor trapping effect. However, if the hanging height is too high, it increases the difficulty of hanging and increases the cost of use. Therefore, the optimal hanging height of traps should be 1.6-1.8 m above the ground.

According to the tobacco planting cycle in Central Guizhou Province, it is recommended to focus on the control of the first generation of S. litura. The sex pheromone devices (adding sex pheromones) should be se up before April, so as to reduce the initial population of S. litura of the first generation, thereby reducing the mating rate. In this way, the number of larvae at 2-3 instars can be controlled during the growth period of tobacco plants (June-July), which can reduce the harm of S. litura larvae to fluecured tobacco, thereby achieving green control effect. The second key control period is the peak mating period of the fifth generation S. litura, that is, from the end of October to the beginning of November. It can be done by replacing the sex pheromone lures to reduce the mating rates of S. litura of the fifth generation. In this way, it can reduce the number of overwintering pupa, thereby decreasing the initial population amount of adults of the following year. In the meantime, it can also reduce the number of larvae of 2-3 instars of the first generation of S. litura during the seedling period of tobacco (April-May), thereby achieving the effective control of S. litura.

References

［1］ CHEN TH, CHEN CX, JIANG KJ, et al. Occurrence regularity of Prodeinia litura and a new forecast method［J］. Entomological Knowledge, 2001, 38(1): 36-39.

［2］ WU SC, GU YZ, WANG DS. Resistance of the tobacco army moth (Prodenia litura) to insecticides and its control［J］. Acta Agriculturae Shanghai, 1995, 11 (2): 39-43.

［3］ NIE NS, HUANG SJ, LONG QL. Insecticideresistance and control strategy for common cutworm, Spodoptera litura (Fab.)［J］. Acta Agriculturae Jiangxi, 2007,19(7): 51-54.

［4］ CHEN L, LI B, PU GQ. Insecticideresistance causes and the control strategy for Spodoptera litura［J］. China Sericulture, 2009, 30(2): 16-19.

［5］ FAN XJ, LI Y, LI Y, et al. Research progress of insect sex pheromones［J］. Journal of Anhui Agricultural Sciences, 2010, 38 (9): 4636-4638.

［6］ YAO ST, ZHENG YL, ZHANG YY, et al. Preliminary study on several sex pheromones for trapping and controlling Spodoptera litura Fabricius in field［J］. Plant Protection, 2007, 33(4): 127-129.