In 2019, the grassland moth has little impact on China's crop yield, but 2020 will be a bigger challenge...
In January 2019, the grassland moth invaded Jiangcheng County, Yunnan Province, China, and has gradually spread to 26 provinces and regions across the country, involving 1538, with a maize occurrence area of 1.065 million hm2, and caused harm to 14 crops such as sugarcane, sorghum, millet and wheat, and only the northeast region of China was spared in 2019.
At the beginning of 2020, due to the gradual hatching of the grassland leaf moth that entered the overwintering insect state, the time for the insect source to migrate to the Yangtze River Basin in the spring will be about one month earlier than in 2019. Its spread to the Huang-Huai-Hai region and the northeast region will also be advanced.
At this time, it is the seedling stage of summer corn in Huanghuaihai and the new leaf period of spring corn in the north. And the number and harm of individuals hatched locally after wintering are higher than those of migratory individuals from afar. In 2020, it may be necessary to face the dual pressure of indigenous insect sources and migratory insect sources, so its prevention and control situation will be more severe than in 2019.
What is the Meadow Leaf Moth?
Spodoptera frugiperda, also known as fall armyworm, is an omnivorous pest native to the lepidoptera noctiaceae family Lepidoptera noctificinalis native to tropical and subtropical regions of the Americas. The insect can be divided into corn type and rice type according to host preference, corn type preference corn, sorghum and cotton, etc., rice type preference rice type and so on. The main invading crops in China are corn types, which have a wide range of hosts, including corn, sweet corn, sugarcane, sorghum and other nearly 200 kinds of crops. The insect can cause harm in all growth stages of the corn plant, and in the uncontrolled corn field, a single larva can cause the corn leaf center to partially wither, unable to grow new leaves and die.
After the invasion of the western part of Yunnan, the grassland night moth mixed with the twill night moth in the winter corn field. Therefore, it is very easy to confuse the two worms in the process of investigation.
From the United States
Native to the Americas, the meadow moth spread to Nigeria, Ghana and other regions of Africa through cargo transportation in 2016, after which the meadow moth spread to eastern and southern Africa, and by April 2017, many countries in sub-Saharan Africa had been affected by insect infestations. In May 2018, the grassland moth was discovered in Yemen and spread to India in the same month. Subsequently, in 2019, China, Vietnam, Malaysia, Indonesia, Cambodia, the Philippines and other Asia-Pacific countries have successively detected the grassland night moth. From June to July 2019, the grassland nightcrawler was found in Egypt, South Korea and Japan. In February, according to FAO, the grassland nightcrawler was found in Australia. At present, the grassland moth has been found in 111 countries around the world.
A global hazard
In Florida, USA, where the grassland moth originates, the pest infestation has been relatively stable, reaching a relatively sustainable control balance, but it can still cause a 20% reduction in corn yields.
Losses were worse in relatively economically backward areas: 72 per cent in Argentina, 40 per cent in Honduras and 34 per cent in Brazil. In 2017, insect infestations spread across Africa, resulting in a maize yield loss rate of between 21% and 53%, reducing production by 8.3 million to 20.6 million tonnes and causing losses of US$2.481 billion to US$6.19 billion. In 2019, Thailand suffered from the invasion of the grassland moth, because of the control of the grassland moth, the increase in the cost of control per hectare of crops is 40-80 US dollars, but due to the cheaper pesticides used in Thailand, the actual effect is not good enough, corn production is still reduced by 25%-40%, and the economic loss is 130-260 million US dollars.
However, according to the report of Huatai Securities, due to the timely prevention and control of grassland moth in China in 2019, we believe that the grassland moth in 2019 has little impact on China's crop yield. In 2018, China's annual output of corn was 257.1739 million tons, and the annual output of corn in 2019 was 260.77 million tons, up 1.4% year-on-year; in terms of prices, the average price of corn in 22 provinces and cities in 2018 was 1.95 yuan / kg, and in 2019 it was 1.98 yuan / kg. But 2020 will be an even bigger challenge.
Route of invasion
According to the information provided by Dr. Wu Qiulin:
Judging from the source of migration, the grassland night moth is divided into foreign insect sources and domestic insect sources.
The overwintering areas of the meadow moth's mature larvae and pupae are located between the isothermal line and the annual breeding area at 7°C in January, which roughly include southern Zhejiang, central and southern Jiangxi, southern Hunan and southern Guizhou.
There are four migration paths for the foreign grassland moth to enter China:
First, from northeast India, Myanmar and other places to follow the southwest monsoon from May to June into the southern Nyingchi and Qamdo regions of China's Tibet Autonomous Region (Tibet referred to as Tibet);
Second, Myanmar and Laos moved into Yunnan and other places with the southwestern air current;
The third is that the Indochina Peninsula moved into Guangxi, Guangdong and Hainan with the southwest wind in late winter and early spring;
Fourth, the Philippines moved into the southeast coast and Taiwan with typhoons or tropical cyclones in July and August.
The process of occurrence and development of alien pests includes three stages: invasion, colonization and outbreak. In 2019, the grassland moth completed the invasion and colonization process in China, and will enter the outbreak stage in 2020.
As far as the general law of the occurrence dynamics of alien pests is concerned, when the natural ecological control effect of the native area is removed from the natural ecological control effect of the native area and enters a new suitable habitat, the population occurrence rate is 5 to 10 times that of the native habitat.
The difficulty of prevention and control
One of the main reasons for the global ravages of the grass leaf moth is its susceptibility to drug resistance:
As of 2017, the grassland moth in the Americas has developed resistance to at least 29 insecticides, including the chemical insecticides carbamates (subgroup 1A), organophosphorus (subgroup 1B), pyrethroids (group 3), and Bacillus thuringiensis Cry1F protein, which have a known mechanism of action. However, the use of different pesticides has a greater impact on their resistance.
The prevention and control of the grassland leaf moth is not easy, but it is not impossible, according to the principle of integrated pest management, the author screened the N different ways of death of the grass leaf moth:
Method of Death 1
Agricultural control: establish maize enticing belts
Agricultural measures can reduce populations and hazard levels by creating an environment that is not suitable for grassland moths to occur on key crops.
The grassland moth has a strong egg-laying preference for corn, and can plant a certain proportion of corn as a trap belt in the field of wheat, peanuts, millet, kale, sugarcane and other crops to attract the grassland moth to concentrate on spawning. After planting corn and ox tendon grass in the field or field to induce the grassland night moth to lay eggs, its egg pieces are removed quickly with chemical pesticides or other methods.
The above pictures are: 1. Strips are planted with corn to shelter wheat; 2. strips are planted with corn to shelter peanuts; 3. corn is planted in the field to shelter peppers; 4. Corn is planted around the edge of the field to shelter a variety of crops.
Method of Death 2
Biological control: parasitic wasps
Trichogramma belongs to the family Red-eyed bees of the family Hymenopterae and is a class of egg parasitic wasps. Adults lay their eggs in the host egg so that the host egg cannot hatch, thus achieving the purpose of eliminating pests. Therefore, the red-eyed bee is an important natural enemy of many agricultural and forestry pests, and it is also the most studied and widely used egg parasitic wasp in the biological control of pests in the world. Red-eyed wasps are multi-feeding egg parasitic wasps with a wide range of hosts.
Most red-eyed wasps can parasitize insects of the moth family Pynaidae and noctuidae. An investigation of the natural enemy resources of the origin of the grassland nightcrawler found that 11 species of red-eyed wasps can parasitize the eggs of the grassland nightcrawler. The red-eyed wasp is an effective method of parasitic wasp control.
Method of Death 3
Biological control: parasitic flies
Winthemia trinitatis (Thompson) belongs to the family Dipterae parasitic flies, is a parasitic fly of the grass nocturnal moth larvae, the female fly lays eggs in the grassland nocturnal moth 5 or 6 year old larvae close to the head of the body, the parasitic fly larvae hatch will invade the grass nocturnal moth larvae, delaying the development of the host pupal stage. Field surveys showed that the parasitic rate of the parasitic fly on the elderly larvae of the grassland nightcrawler could reach 30%, which effectively reduced the population of the grassland nightcrawler.
Method of Death 4
Biological control: predatory predators
Coleomegilla maculate (De Geer) belongs to the Family Cholephyllaceae, adults are about 6 mm long, generally red, and have 6 dark spots on each coleopept. Both adults and larvae feed on aphids, mite eggs, and larvae of a variety of insects such as the grass moth. In addition, the big-eyed bugs, cunning flower bugs, and some of the foot beetles are predatory predators of the grass leaf moth.
Dead Method 5
Biological control: attracting hormones
The use of sex pheromones to lure male moths into traps can effectively control the number of grass moths. However, the disadvantage is that the prevention and control effect is not ideal, and the method of sexual attraction is often used for field quantity monitoring.
Method of Death 6
Physical control: insect trap lamp
Adult grass leaf moths have a strong tendency to the green light band and yellow light band, and can be concentrated and killed after luring and gathering by insect attractants.
Method of Death 7
Biological control: Bacillus thuringiensis
The grass moth is highly sensitive to BT proteins.
Method of Death 8
chemical control
At present, China recommends a series of biological and chemical agents for the prevention and control of grassland nocturnal moth, mainly including methylamino avermectin, indinale, chlorantran benzamide, high-efficiency cypermethrin, liceme urea, kale nocturnal nucleo-type polyhedral virus, scarab green zombie and other single doses and their compound agents.
Death Method 9
Plant extracts
Studies have shown that more than ten species of neem plants, including chloroform, hexane and ethanol extracts from neem and neem seeds, can delay the development of the grassland nightcrawler and cause its death. In addition, methanol extracts from the peel, seeds and pulp of balsam trees can also lead to stunting, increased mortality, and decreased reproductive capacity of adults. 1% bitter vine emulsion is very effective in insecticidal use, while 0.5% matrine aqueous agent only has a good insecticidal effect on hatching larvae.
Summary
At present, the control of grassland moth is mainly through the implementation of a comprehensive control strategy based on chemical control to solve the problem of emergency prevention and control, such a technical route prevention and control investment costs are high, there are certain food safety risks and high environmental safety risks. Since invasive and colonized grassland moths have developed high resistance to organophosphorus, pyrethroids, carbamates and nicotinic chemical insecticides, the widespread use of amides and other few highly effective insecticides will soon cause resistance.
Once the grassland moth becomes resistant to several types of pesticides that are still highly effectively controlled, there will be a passive situation in production that lacks effective control measures, which is likely to reproduce the serious consequences of the loss of control of the cotton bollworm in the 1990s.
The author believes that the prevention and control of the grassland leaf moth also depends on the development of modern agriculture and three-dimensional control. Biological and agricultural control is the mainstay, supplemented by chemical control, combined with the promotion of anti-BT maize, the economic hazard level of the grassland leaf moth is comprehensively controlled.