Cotton is an industrial plant with a high commercial value. It is used in various fields such as textile, food (cotton oil), gunpowder industry, paper, and furniture production. One of the most important problems encountered during cotton production is insects that feed on cotton and cause economic loss. The intensive amount of pesticides is used by the producers for the control of pest insects. As insects gain resistance to pesticides over time, the amount of chemical pesticides applied is gradually increasing. Chemical products are quite harmful to both living things and the environment. For this reason, there is a need to popularize biological control methods instead of using pesticides to control pests. In this chapter, detailed information about insect species causing damage to cotton and biological control methods is given.
- cotton pests
- biological control
Biological control is the use of predators, parasitoids, or pathogens to control the population of the target organism. In biological control, predators and parasitoids are methods based on the use of beneficial insects against the target organism, while pathogens consist of microorganisms that cause disease or death of the target organism. These microorganisms originate from fungi, nematodes, bacteria, protozoa, and viruses and are bioinsecticides that can reduce harmful insect populations below the economic damage threshold in a short time . Studies on widespread use of these pathogens have gained importance because, unlike chemical substances, they are specific to the host, do not cause harm to nontarget organisms, do not leave residues in nature, and are environmentally friendly and reliable . For this reason, as in other products, cultural measures and biological control should be the first preferred control methods in cotton . Chemical control should be used as the last alternative. It is more important in terms of biological control to protect the natural enemies present in the grown cotton . In order to keep pests below the economic damage threshold, natural enemies and friendly microorganisms should be given an opportunity.
In this chapter, harmful insects that feed on cotton plants and cause economic loss and biological control methods applied against them are given.
2. Cotton pest insects
The pest insects’ variety and density vary according to the development stage of the cotton plant and the geography where it grows. In this section, insects that cause economic loss by feeding on cotton are classified under two headings as main pests and other pests.
2.1 Main pest insects
Insects that are the main pests of cotton are: cotton aphid (
2.1.1 Cotton aphid,
glover (Hemiptera: Aphididae) A. gossypii
Adult individuals of the pest, which have an average maturity of 7 days, have the ability to procreate offspring immediately. Since aphids reproduce by parthenogenetic reproduction, they have the ability to form large colonies in a short time . This insect damages cotton in several different ways. Plant sap of cotton is rich in sugar, yet low in protein. For this reason, aphids need to take large amounts of sap to obtain sufficient protein. Excess sugar is secreted in the form of honeydew and makes the crop and fruit sticky. Black mold fungi (
2.1.2 Cotton jassid,
Amrasca bigutullaIshida (Hemiptera: Cicadellidae)
2.1.3 Tobacco thrips,
T. tabaciLindeman (Thysanoptera: Thripidae)
2.1.4 Cotton leafhoppers,
Empoasca decipiensPaoli and Asymmetrasca decedensPaoli (Hemiptera: Cicadellidae)
Cotton leafhoppers, which are seen in dense populations in the early period in cotton fields, feed on the vegetative and generative parts of the cotton plant by sucking, affect the development of the plant negatively, and cause shedding especially in the generative organs . It is known that hairless and broad-leaved cotton varieties are more adversely affected by the population growth of leafhoppers [32, 33]. In addition to the sucking damage, it gives to the plant, cotton leafhoppers are also harmful because of toxic secretions into the plant body. The toxic substances cause hypertrophy in the phloem tissue cells of the leaf and blockages in sap transport. Biological control of cotton leafhoppers is done with the use of natural enemies. Among these natural enemies, the most successful are:
2.1.5 Two-spotted spider mite,
Tetranychus urticaeKoch (Acarina: Tetranychidae)
2.1.6 White tobacco fly,
B. tabaciGennadius (Hemiptera: Aleyrodidae)
Since whiteflies feed by sucking the sap of the cotton plant during periods of high population density, plant leaves are greatly damaged. This damage to the leaves can affect fruit development and lead to a decrease in yield.
Fruits become sticky due to the sweet juice left on them. Dirt sticks to the fruit, and the development of dark mold (Cladosporium spp.) accelerates, so the fruit becomes unsaleable. In severe cases, the fruit rots.
However, dark mold can also develop on the leaves, as a result of which the amount of photosynthesis and transpiration is reduced in cotton plants [41, 42]. The consumption of plant sap by whiteflies and the secretion of fresh juice also reduces the esthetic value of the crop. This is a very important problem, especially in ornamental plants. Besides, larvae inject enzymes into the plant, altering the plant’s normal physiological processes [43, 44]. Many effective natural enemies are used in the control of
2.2 Other pest insects
Under this section of “other pest insects,” information is given about the insects that cause significant damage to the cotton plant by causing epidemics in some years. These insects are cotton bollworm (
2.2.1 Cotton bollworm,
Helicoverpa armigeraHübner (Lepidoptera: Noctuidae)
2.2.2 Pink bollworm,
Pectinophora gossypiellaSaund (Lepidoptera: Gelechiidae)
The larvae of
2.2.3 Egyptian bollworm,
E. insulanaBoisduval (Lepidoptera: Noctuidae)
A. ipsilonHufnagel, Agrotis segetumSchiffer (Lepidoptera: Noctuidae)
Cutworms larvae damage cotton seedlings by cutting them. It damages cotton plants by cutting from the two-leaf period, which is the basic development period, to the 6-8-leaf period, and cuts the young plants from the soil surface. However, they can also cut underground under conditions where the soil is soft and the soil moisture is low. Especially large larvae pull the cut plants under the ground and eat their leaves. They do damage by taking turns. Damage is greater in late planting areas and rainy spring months. Damage may occur to a degree that requires replanting . Biological control agents, including fly and wasp parasites, disease organisms, and predatory beetles, continually reduce cutworm populations . However, entomopathogenic nematodes are used successfully in the control of cutworms living under the ground [75, 76].
2.2.5 Beet armyworm,
S. exiguaHübner (Lepidoptera: Noctuidae)
2.2.6 Cotton leafworm,
Spodoptera littoralisBoisduval (Lepidoptera: Noctuidae)
2.2.7 Flower thrips,
F. intonsaTrybom, F. occidentalisPergande Thysanoptera: Thripidae
Flower thrips, especially in late planting cotton fields, in case the population is very high, adults feed on flowers and larvae feed mostly on the cocoons, causing shedding of flowers and newly formed bolls and early opening of mature bolls. However, no economic damage is caused in the cotton fields of our country. Species belonging to this genus are harmful, especially by sucking on the flowers and flower buds of the cotton plant. In addition, large and mature cocoons cause the formation of cocoons that do not fully open and are called “Crispy cocoons” as a result of the suction damage that occurs in dense populations . In the biological control of flower thrips, predatory insects of the genus
2.2.8 Plant bedbugs,
Creontiades pallidusRumb, Lygus gemellatusHerrich-Schaffer, L. pratensisLinnaeus, Lygus italicusWagner (Hemiptera: Miridae)
Plant bedbugs feed by sucking all the organs of the cotton plant due to their stinging and sucking mouth structures. The absorbed place deformed as a result of the toxic substance secreted and then turns black. If the damage occurs on the leaves, the leaf tissue dies over time in the place where it is absorbed. The leaves become perforated or segmented. These pest larvae do their main damage by feeding on generative organs . Most of the scallops, flowers, and small bolls that are damaged by the suction are shed. As a result of casting, a decrease in the product occurs, as well as a delay in maturation. In sucked cocoons, the seed weight decreases. This reduces the seed yield . In addition to generative organ casting, they also cause deformities such as abnormal comb formation, elongation of plant height, and an increase in the number of nodes on the branches. Predators (
With the increasing importance of cotton plants both in commercial and domestic use, harmful insect species found in cotton fields and their damage to the product have started to gain more importance. Both the suitability of the leaf surface (especially the hairless cotton leaf) and the high irrigation rate of cotton attract harmful insects. For this reason, there are at least 20 agricultural pest insect species on the cotton plant. When cotton producers see the presence of harmful insects on the product, they prefer the use of chemical pesticides in terms of ease of application in a short time. However, the use of chemical products has long-term negative effects on natural enemies (predators and parasites), other nontarget invertebrates and vertebrates, the environment, nature, and human health. Besides, unnecessary and excessive use of chemical pesticides causes harmful species to resistance. Therefore, the use of chemical drugs should be reduced as much as possible, and biological control agents should be preferred instead. Predator and parasitoid species are used quite successfully for the biological control of cotton pests. In addition, studies on the preparation and marketing of commercial formulations of entomopathogenic microorganisms continue all over the world. In recent years, consumers have started to prefer organic products for all products. In the food and clothing sectors, products containing organic cotton (especially baby clothes) are preferred. For this reason, the development of biological control agents and the cultivation of natural enemies should be supported, and producers should be encouraged to apply them in nature. In particular, the licensing procedures required for placing organic biopesticides on the market involve a very difficult process in some countries. Facilitation of this process by the relevant ministries of agriculture is one of the most important factors that will increase large-scale biopesticide production.