Cotton bollworm belongs to the Lepidoptera noctuidae family, in the vegetable area, it is mainly harmful to tomatoes, eggplants, cowpeas, green onions, amaranth, kale, pumpkin, etc., with larvae to eat the buds, flowers and fruits of crops, but also harmful to young stems, leaves and buds. After the bud is damaged, the buds open and fall off after 2 to 3 days; after the fruit is damaged, it is hollowed out or a hole is formed. After the insect is infested, moth holes and insect droppings are common, and the damage in the field is obvious and easy to identify.
Watermelon is one of the host plants of the cotton bollworm, but the cotton bollworm is rarely seriously harmful to watermelon. In the autumn of 2019, the author found that the cotton bollworm was harmful to the watermelon in the Beijing shed, and the moth on flower buds and young melons was serious, and the occurrence of the pest, the analysis of the possible causes and the prevention and control techniques are briefly described as follows.
<h1>1 Occurrence of cotton bollworm in the northern region</h1>
Cotton bollworm has four stages of development: egg, larvae, pupae and adult, with the larval stage being the most common. Adults (commonly known as moths) are about 15 mm long with a wingspan of 12 to 39 mm (Figure 1); the eggs are hemispherical and have a high top bulge (Figure 2).
Fig. 1 Adult cotton bollworm
Fig. 2 Scattered spawning of eggs of cotton bollworm
Pupae overwinter in the root soil of the host crop, and after overwintering adult insects feather in the spring of the following year, they lay more eggs on wheat, tomatoes, peas and other crops, causing harm.
Adults prefer to inhabit the back of leaves or shade during the day, and begin to move at dusk, absorb nectar to supplement nutrition, have a strong ability to fly, and have obvious phototropism and tenderness.
Cotton bollworm eggs are scattered, and the amount of eggs laid by a single female can exceed 1000 grains; it grows to the 2nd instar larval stage and begins to feed on the flowers, young branches, young buds and fruits of the crop; after 4 years of age, it enters the overeating stage, and the field is obviously harmful.
<h1>2 Cotton bollworms are pests on watermelon in Beijing</h1>
In late August 2019, the author found that the cotton bollworm was seriously harmful to watermelon in the plastic greenhouse of the test base in Haidian District, Beijing. Field surveys found that cotton bollworm pests have three characteristics:
First, only the watermelon was seriously harmed, and the thin-skinned melon and thick-skinned melon in the same greenhouse were not harmed;
Second, there are obvious differences in the appetite and degree of harm of cotton bollworms to different watermelon varieties, and the harm rate of oval watermelons is as high as 40%, and the harm rate of round watermelons is close to 20%;
Third, cotton bollworms are mainly harmful to the buds and young melons of watermelons, the flower buds are penetrated, the flower buds are eaten (Figure 3), the young melons are eaten seriously, and the moths on a single young melon can exceed 10 at most, and the larvae leave feces at the decay place after the infestation, contaminating the fruit (Figures 4 and 5), showing their habit of "drilling moths".
Fig. 3 Cotton bollworm is a bud that harms watermelon
Fig. 4 Cotton bollworm larvae and their moth-eating holes caused by feeding on young melons
Fig. 5 Cotton bollworm drill moth larvae feeding as a pest
The young melons that have been mothed by cotton bollworm larvae are deformed (Figures 6 and 7) and completely lose their commodity value. At this time, the cotton bollworms found in the field are all young larvae, and no elderly or mature larvae are found.
Fig. 6 and 7 Cotton bollworm burrowing moths to eat young melons causes fruit deformity
<h1>3 Analysis of the causes of the occurrence of cotton bollworms</h1>
According to previous surveys and field findings, cotton bollworms in the northern region are less harmful to melon crops and more to tomatoes, amaranth, kale and other crops. Preliminary analysis of the reasons for the serious damage of cotton bollworms in the melon shed in 2019 may have the following three points.
First, cotton bollworm is omnivorous, cucurbitaceae crops are also its host, at this time watermelon is in the bud stage and young fruit stage, suitable for its feeding and harm; around the shed planted cabbage and cabbage and other cruciferous vegetables, but the investigation did not find cotton bollworm as a pest, may be because the cotton bollworm spawning peak and melon field buds, young melon stage coincides, attracting its population to directly lay eggs on melon fruits and buds, larva hatching caused by harm.
Second, the most suitable temperature for the occurrence of cotton bollworm is 25 ~ 28 ° C, relative humidity of about 70%, suitable for arid environmental conditions; according to literature reports, Beijing area in August should be the occurrence time of the third generation of cotton bollworm, at this time the external temperature in Beijing is 22 ~ 30 ° C, less rainfall, conducive to the hatching of cotton bollworm eggs, but also has suitable conditions for its breeding.
Third, there are many kinds of natural enemies of cotton bollworms, such as parasitic wasps (cotton bollworm tooth lip bee, borer hanging cocoon bee, medium red side groove cocoon bee, etc.) and bacteria, fungi, viruses. According to reports, in the vegetable fields on the outskirts of Beijing, the parasitic rate of the first generation of larvae is generally 28% to 37%, and the proportion of individuals parasitizing the eggs of the second generation of cotton bollworms by red-eyed bees can be as high as 51%. However, the watermelons surveyed this time are cultivated in plastic greenhouses, and the lack of natural predators in the protected area is also conducive to the smooth establishment of populations and pests of cotton bollworms.
<h1>4 Cotton bollworm control technology</h1>
<h1>Agricultural control</h1>
Cotton bollworm field infestation symptoms are obvious, can be combined with the whole branch of the branch to beat the other agricultural operations for artificial egg picking and larvae; cotton bollworm pupae in the soil overwintering, so in the area where the cotton bollworm occurs seriously, you can carry out deep ploughing after the autumn crop harvest, directly kill the overwintering pupae, or destroy the pupa chamber, making the pupa difficult to feather, which can significantly reduce the occurrence of the next generation; in the vicinity of the melon field prone to the occurrence of cotton bollworm, plant celery, carrot, onion and other honey source plants to induce the first generation of adult cotton bollworms. This is followed by spraying of highly effective chemical insecticides for concentrated killing.
<h1>Physical control</h1>
Black light or frequency-vibration insecticidal lamps can be set up in the field to monitor and trap cotton bollworms. Studies have shown that the number of female insects trapped by frequency vibration insecticidal lamps is higher than that of male insects, and compared with black light lamps and high-pressure mercury lamps, the induced benefit-harm ratio is the lowest, so the amount of pesticide use can be greatly reduced.
<h1>Biocontrol</h1>
Male moths can be trapped by hanging cotton bollworm attractants in the field. When using sexual attractants, a water basin trap or a specific trap can be used, according to the recommended dose of the manufacturer, replace the core every 20 to 30 days, and pay attention to cleaning the adult cotton bollworm in the basin every 2 to 3 days, and replenish the water in time. The sexual trap method is more effective when used in a large area of continuous tablets.
Places with conditions can also choose to protect and release natural predators such as grasshoppers, red-eyed bees, and small flower bugs. When releasing red-eyed bees for control, the bees are usually released 2 to 3 times in a row at the beginning and peak of the spawning period of cotton bollworms, and 15,000 to 20,000 heads per acre are released each time, which can also be determined according to the amount of eggs, and can be placed several times when the amount of eggs occurs;
In addition, in the incubation period of cotton bollworm larvae to the peak of the second instar, you can also choose to use The Suyunjin bacillus suspension agent (6000 IU/ μL), with a dosage of 400 to 500 mL per mu; the recommended dose of 1/5 to 1/3 of the chemical insecticide can also be added when it is used to improve the insecticidal effect; or the cotton bollworm karyopolytic polykerratic virus 2 billion PIB/mL suspension agent, the dosage of 50 to 60 mL per mu, sprayed with water, the appropriate period of administration is the peak of egg production.
<h1>chemical control</h1>
It has been reported that bollworms are currently resistant to a variety of pesticides to varying degrees. For example, the resistance of bollworm to octylthion and high-efficiency cypermethrin in North China and East China showed an upward trend, with a resistance multiple of more than 20 times, of which the resistance to permethrin agents in Binzhou, Shandong Province, exceeded 200 times, and the local resistance of p-amino avermectin benzoate showed a moderate level of resistance. Therefore, the selection of agents should be rationally carried out on the basis of resistance monitoring.
In addition, cotton bollworm is a moth-like pest that needs to be closely monitored, and its egg hatching period is seized to the peak of the second-instar larvae for drug control, and then applied until the moth enters the fruit, and the prevention and control effect will be significantly reduced.
The types of chemical agents available and their dosage per mu are as follows: 1% methylaminoavermectin benzoate emulsion 60 to 80 mL, or 10% cypertoxamide dispersible oil suspension 19.3 to 24 mL, or 6% mevin flulingurea 32 to 36 mL, or 20% chlorpyrifosine benzamide suspension 7 to 14 mL, or 5% fludilurea emulsion 110 to 140 mL, or 14% chlorpyrifos perchlorofluorocystes suspension - suspension 15 to 20 mL, or 6% chlorpyrifos perchlorine fluorine microcapsulation suspension 15 to 20 mL, or 6% Ethyl polybactericide suspension 20~40mL. Use the field with water spray, every 7 days, 2 to 3 times continuously. Agents are administered in rotation.
Source: This article is excerpted from the article "The Pest of Watermelon by Beijing Autumn Cotton Bollworm and Its Prevention and Control" in the 10th issue of China Vegetables. Author: Wang Shaoli Wang Huaisong Zhang Youjun Gu Nan, Unit: Institute of Vegetables and Flowers, Chinese Academy of Agricultural Sciences, College of Forestry, Henan University of Science and Technology.