With the help of LED lights, lychee production base uses light repellent method to prevent and control stem borers

Lychee and longan are native to China and are a dominant and valuable fruit in southern my country. The area and output of lychee and longan in my country ranks first in the world, mainly distributed in Guangdong, Guangxi, Fujian, Hainan, Sichuan and other places. In 2021, the total lychee and longan area nationwide is 12.43 million acres, with an annual output of 4.81 million tons.

Among them, 4.8 million acres of lychee and longan are planted in Guangxi, with the planting area and output ranking second in the country after Guangdong. It is an important economic crop for Guangxi fruit farmers to increase production and income and consolidate poverty alleviation. Guangxi lychee and longan are mainly distributed in hot areas with superior light, temperature and water conditions, rich vegetation, complex biodiversity, and more than 200 species of pests and diseases. Among them, the lychee stem borer has the greatest impact on the yield and quality of lychee and longan.

The larvae of the lychee stem borer mainly cause damage by eating fruits, causing a large number of "worm droppings". Generally, the yield loss is 30%-40%, and in severe years it can be as high as 60%-90%. In the past, the control of lychee stem borer mainly relied on spraying chemical pesticides. However, after hatching, the larvae bore directly into the fruit from the bottom of the egg shell. The entire larval stage caused damage inside the fruit, resulting in a very short time for pesticides to contact the larvae. The surface of the pupae is also covered with a protective layer of cocoon-like silk film, so the pesticides cannot reach the pupae, and the control effect is not good.

For this reason, fruit farmers can only continue to spray chemical pesticides every 5-7 days to kill adults and eggs. The number of applications per season ranges from 5-10 times. This not only increases the cost, but also affects the quality and safety of the fruit and pollutes the environment.

In order to effectively control the damage caused by the lychee stem borer and improve the quality of lychee and longan, Liao Shichun's team pioneered the light repellent method to prevent and control the lychee stem borer and successfully applied it on a large area. This technology takes advantage of the extremely photophobic biological characteristics of the lychee stem borer and hangs lights in the orchard at night to repel or interfere with the insect's behavior. It is a technology that organically integrates physical and ecological prevention and control.

According to reports, in 2013, researcher Liao Shichun was hired as a pest control expert in the Guangxi Lychee and Longan Innovation Team of the National Modern Agricultural Industry Technology System. After in-depth investigation, he believes that the development of Guangxi's lychee industry is mainly faced with two major problems: aging of varieties and serious damage from lychee stem borers, which seriously affects output and quality, and lacks market competitiveness, which restricts the healthy development of the lychee and longan industry.

In order to effectively predict the occurrence pattern of lychee stem borers, Liao Shichun initially tried to use light traps to capture adult insects. After repeated trials, he found that he could not lure any insects. He also led the team to conduct repeated experiments by changing different spectrums such as white light, red light, yellow light, green light, and purple light, but still found nothing.

Just when the team members thought that light trapping would not work, Liao Shichun was not reconciled. He said: "Since lights cannot attract insects, why don't we think in reverse and try whether night lights will have repellent behavior on adult insects?" So he began to raise adult insects for indoor experiments to observe the impact of nighttime light on their normal behavior.

Sure enough, after repeated experiments, it was found that under normal circumstances, the average egg period of female lychee stem borer is 12.33 days, and the average number of eggs laid is 136.3 eggs per head. However, after interference with artificial light at night, the average egg period of female insects was shortened to 0-3.33 days, and the average number of eggs laid was only 0-0.47 eggs/head. Secondly, nighttime light also has a significant inhibitory effect on the ovarian development of female worms. The egg-laying period is significantly shortened, and the number of eggs laid is significantly reduced or even impossible to lay eggs and reproduce. This proves that nighttime light can inhibit the egg-laying and reproduction of lychee stem borers. Afterwards, the team conducted research on the effects of different light intensities on female oviposition, and found that white light above 10 Lux can effectively inhibit adult oviposition.

From 2015 to 2018, Liao Shichun’s team and Gu Yaliang’s team from the Qinzhou Institute of Agricultural Sciences conducted small-area field experiments in Pubei County, Qinzhou City, and found that the fruit bore rate of all fruit trees with lights hung at night was zero, and the effect exceeded expectations.

In early 2019, Liao Shichun set out to organize a large-scale trial demonstration of the light-repellent method to prevent and control litchi stem borer technology. He believed that it was crucial to select representative demonstration sites. How to find this demonstration point?

Through understanding, Liao Shichun found a 15-acre March Red lychee orchard near Longwu Farm in Lingshan County. The trees are nearly 30 years old and 5-7 meters tall. Due to the poor quality of the lychees in previous years and the high tree crown, the orchard was almost out of control. The occurrence of lychee stem borers was very serious every year. It was called a "worm nest" by nearby fruit farmers. The surrounding orchards were deeply affected but there was nothing they could do.

After an on-site inspection, Liao Shichun found that the canopy of the orchard was too high to apply pesticides. This orchard is an excellent place to test whether this new technology is effective. The lights will be turned on on the evening of April 9, 2019 until harvest. That is, a 20W LED white light is installed in the southeast, northwest and northwest of each lychee tree. The bottom height of the bulb is 80-100cm higher than the top of the crown, so that the light fully covers the crown surface and the light intensity is ≥10 Lux. The lights are turned on every night from 19:00 to 6:00 the next day, and no pesticides are applied during this period.

On May 17, 2019, an on-site inspection by plant protection and fruit experts showed that the fruit borer rate in the light-repellent method for preventing and controlling lychee stem borer technology demonstration area was 0 (the fruit borer rate in the surrounding fruit growers’ normal pesticide control areas was 35%). The expert group unanimously believes that this technology is effective, easy to operate, saves labor and money, and is easily accepted by fruit farmers. It is a true physical green prevention and control technology.

Although turning on lights at night effectively controls lychee stem borers, will it attract other pests? The team's research found that the number of lepidopteran insects in lighted orchards at night is far lower than that in unlit orchards, and there are relatively more coleopteran insects. They can be trapped and killed by installing frequency-oscillating lights in lighted orchards.

This proves that large-area lights at night will not attract lepidopteran insects from surrounding orchards to cause damage, but may inhibit other lepidopteran pests from causing damage. At the same time, research has found that adults of lychee stem borers in orchards with lights on at night will only rest on the branches until they die, and will not fly to nearby orchards that are not lit up to cause harm. This also relieves farmers from worries about using this technology.

From May to June 2019, Liao Shichun's team teamed up with the Lingshan County Agricultural Science Research Institute and the Qinzhou Agricultural Science Research Institute to establish two technical demonstration bases for the prevention and control of lychee stem borers using light-repellent methods (30 acres of Guiwei lychees in Lingshan County and 10 acres of Feizixiao lychees in Pubei, Qinzhou). The average on-site borer fruit rate was only 0.5%, which was far lower than the 5% required by the market.

From 2019 to 2022, the team established more than 10 technical demonstration bases for the prevention and control of lychee stem borers using light repellent methods in Pubei, Lingshan, Guiping, Beiliu and Hengxian, including March Red, Feizixiao, Guiwei, and Nuclear For Li and other varieties, the test area reached 1,000 acres, and the radiation promotion area was 20,000 acres. The new profit was 33.482 million yuan, the expenditure and consumption reduction was 17.102 million yuan, and the economic benefit was 50.584 million yuan.

News from Qinzhou City Lingshan County Association for Science and Technology shows that according to statistics, the investment cost of the "light-driven swimming method" to prevent and control lychee stem borer technology is 800 yuan/acre/year. Compared with the cost of chemical control of 1,000-1,500 yuan/year, the cost can be saved by 200-500 yuan per mu per year. At present, this technology has been promoted and demonstrated in more than 1,300 hectares of Lingshan County, and is welcomed by the majority of lychee growers.

In addition, the team has invited experts from the Institute of Plant Protection of the Chinese Academy of Agricultural Sciences, the Institute of Plant Protection of the Guangdong Academy of Agricultural Sciences, and the Institute of Plant Protection of the Sichuan Academy of Agricultural Sciences to conduct 12 on-site inspections. The light-repellent method to prevent and control the lychee stem borer has an average control effect of more than 98%.

The light repellent method to control lychee stem borers is the first technology in the world that successfully uses light to prevent and control pests. This technology was selected as the main agricultural technology promoted by the Guangxi Department of Agriculture and Rural Affairs in 2021, and has been widely used by some fruit farmers in Guangdong, Hainan and other places.