Potential of biological control in Brazilian cotton production

Naturally, ecosystems are ecologically balanced, so that organisms, both animals and plants, act in harmony with the environment. Human action through the introduction of artificial production systems promotes, by introducing monocultures to the detriment of diversified crops, a predominance of more adapted organisms, causing instability and risk to the sustainability of agricultural production systems. This is aggravated in successive systems, where the continuous multiplication of host crops for generalist insect pests is encouraged, generating an uninterrupted breeding ground for these arthropods.

Cotton cultivation, known for the large number of organisms that cohabit in the production system, with more than a thousand species between insects and mites, has a small percentage of insect pests responsible for causing economic damage, however, enough to cause serious losses to production, when not properly controlled.

On the other hand, beneficial insect fauna, which plays a key role in regulating environmental balance, has been active in controlling insects, although in many cases they are not sufficient to naturally contain high pest populations in agroecosystems. In cotton, these pests, due to their great capacity to multiply, disperse and cause injuries, are responsible for serious economic losses to production, affecting the sustainability of the production system.

In an attempt to solve pest attacks, farmers prefer to use insecticides whose action is not restricted to insects, but also to natural enemies, which are as susceptible or more susceptible to various types of chemical products. Much more than affecting natural enemies, these chemical products, in addition to their side effects, can be responsible for promoting the resurgence of pests, as well as inducing insects to become resistant to insecticide molecules due to selection pressure. The elimination of the key pest in the agroecosystem is known as a “biotic vacuum”, inducing the emergence of secondary pests, no longer maintained by the action of natural enemies, but also eliminated due to the application of insecticides.

Therefore, it is necessary to understand the potential of biological control and its application in cotton farming. The concept of biological control is based on the fact that different species of organisms are regulated according to the food chain, which is a natural condition in which all organisms need to survive and multiply. Biological control is therefore defined as the action of natural enemies capable of maintaining the average population of the pest at a level below that which would occur without the presence of these beneficial organisms. Biological control (BC) can be exercised basically in the following ways:

1 - Artificial CB: method in which artificially multiplied natural enemies are released in biofactories, using natural or artificial hosts, providing synchrony of occurrence with the target pest in their favor;

2 - CB Natural: It is carried out naturally without human intervention, such as natural insect infestations or epizootics of entomopathogenic fungi. In this case, success depends on environmental factors (physical and biological) that are favorable to the development of natural enemies.

Other modalities that fall within these two types are Classic CB and Conservationist CB, the latter being carried out based on environmental manipulation.

Predators, parasitoids and pathogens are known as natural enemies or biological control agents. The first two are called entomophages and the third entomopathogens. Predators are organisms that need more than one individual to survive and multiply to complete the biological cycle. The main orders of insects that harbor predators are Coleptera, Hemiptera, Neuroptera, Diptera and Dermaptera. Parasitoids are characterized by needing a single host to complete their biological cycle, and can develop inside the host (endoparasitoid) or on the surface of the host's body (ectoparasitoid). The main orders of parasitoid insects are Hymenoptera and Diptera. Entomopathogens are microorganisms that feed and survive on or inside their hosts.

The main natural enemies (predators and parasitoids) of insect pests in cotton are presented below:

• Trichogramma pretiosum (Hymenoptera: Trichogramatidae): Egg parasitoid, especially of Lepidoptera, is one of the most studied macroorganisms in the world. The biological cycle is completed in eight to ten days, having around 15 hosts in the cotton plant. Multiplied in alternative hosts, it is released by drone, in large quantities (inundative release), covering an area of ​​approximately 400 ha, in two passes through the cultivation area.

• catolacus grandis (Hymenoptera: Pteromalidae): parasitoid with a high capacity to locate its prey, develops externally on larvae (3rd instar) and pupae of the cotton boll weevil (Anthonomus grandis) in flower buds. It occurs in synchrony with the weevil, and the attack is carried out by means of paralysis (immobilization of the larva due to the injection of toxins, which can cause the death of the host) and/or by means of parasitism. Flood releases are recommended.

• Bracon vulgaris (Hymenoptera: Braconity): parasitoid that attacks the larvae of the boll weevil in the flower buds and bolls of the cotton plant, causing paralysis by injecting toxin, similar to C. grandis, and/or parasitism. In general, two individuals are generated per boll weevil larva. Its release has been recommended for the moment in which boll weevil larvae are present in the cotton bolls.

• Chrysoperla externa (Neuroptera: Chrysopidae): A very voracious predator, it has a high reproductive potential and a great ability to search for prey. Many insects of different orders are its hosts, such as scale insects, aphids, whiteflies, mites, thrips, as well as caterpillars of different species of Lepidoptera. C. external has the habit of laying eggs with a pedicel. Adult insects are green and have membranous wings. The release has been carried out in the embryonic stage (egg), in a flooding manner and with the use of a drone.

• Podisus nigrispinus (Heteroptera: Pentatomidae): generalist predator, feeds on a large number of hosts. To control prey, inundative releases have been recommended, using fifth instar nymphs, on newly hatched caterpillars in the crop.

• Euborellia annulipes (Dermaptera: Anisolabididae): predator with great attack capacity, it feeds on eggs and insects in the immature stages of different prey from the orders of Lepidoptera, Hemiptera, Coleoptera and Diptera. It is also a predator of larvae and pupae of the cotton boll weevil.

Other agents

Other natural enemies are also recognized in cotton crops:

• Diptera: Toxomerus dispar e Pseudodoros clavatus (Syrphidae);

• Coleptera: Cycloneda sanguinea (Coccinellidae), Calosome spp. (Carabidae), Paederus spp (Staphylinidae);

• Hymenoptera: Lysiphlebus testaceipes (Braconidae), Polistes spp. (Vespidae);

• Hemiptera: geocoris spp. (Geocoridae), orius spp. (Anthocoridae); Brachymeria spp. (Chalcididae), Netelia spp. (Icheneumonidae), Euplectrus comstockii (Eulophidae);

• Arachnids: Crab spiders (Mysumenopsis guyannensis, Synaemopsis rubropunctatus e Xysticus spp.) and web-weaving spiders (Lycosa spp.).

Entomopathogenic agents

There are several entomopathogenic control agents, namely fungi, viruses, bacteria and protozoa. The main entomopathogenic fungi associated with insect pests of cotton crops are beauveria bassiana, Metarhikum anisopliae, Metarhizium (=Nomuraea) rileyi, Verticillium lecanii, entomophthora spp. And Cordyceps spp. The first three species are reported to cause infections in the cotton boll weevil. These infections can be caused in the larvae, pupae and adults of the boll weevil; however, it has been found that the action of the sun is an inhibitory factor in the development of the fungi, inactivating the conidia, so that the application of these microorganisms must take into account the abiotic conditions for effective success.

B. bassiana is one of the most cited fungi with action on insects in cotton crops. In addition to the boll weevil, whose incidence in natural conditions has been evidenced enzootically or epizootics, it has infected lepidopterans (Heliothis spp., helicoverpa e Alabama argillacea) to Bemisia tabaci, among the insects of economic importance. The largest number of studies have been carried out in relation to the control of the weevil. Fungi M. rileyi, M. anisopliae e Entomophthora aulicae attack the genres Heliothis e Helicoverpa; e Paecilomyces fumosoroseus, Aspergillus sp. It is Fusarium sp. the species Bemisia tabaci.

Bacteria are also important pathogens, infecting adult insects via the hemocoel, i.e., the cavity located in the body of arthropods characterized by the presence of hemolymph, as well as through ingestion, i.e., orally. Commercial formulations based on Bacillus thuringiensis have been recommended for inoculative or inundative use, in spraying for the control of A. argillacea and caterpillars of the Heliothinae subfamily complex (Heliothis e helicoverpa). The species Chrysodeixis (=Pseudoplusia) includens, Trichoplusia ni e S. frugiperda are also attacked by B. thuringiensis. There is also a record of the action of the bacteria Pseudomonas aeruginosa em A. argillacea quality Serratia marcescens in the cotton boll weevil.

For the genres Heliothis, helicoverpa there is a record of Granulovirus and Nuclear Polyhedrosis Virus, adding to this the species A. argillacea, for use in biological control. For the weevil, the Chilo Iridescent Virus (CIV) is cited. There are also reports of several microsporidian protozoa causing chronic diseases in species of the genera Heliothis e helicoverpa. The protozoa Nosema heliothidis e Vairimorpha necatrix attack Heliothis e helicoverpa; is Glucea gasti e Mattesia grandis, the weevil.

Advantages of biological control

Advantages of biological control are considered to be the fact that it is compatible with all other pest control methods; it does not cause side effects; it is permanent, depending on the production system in which it is involved; and, in general, it is less costly than chemical control methods. In relation to natural enemies, favorable characteristics for its use are: high efficiency; great host-seeking capacity; short biological cycle; high reproductive rate; adaptability to abiotic and biotic conditions; synchrony and high density-dependence with its host.

Natural enemy releases can be carried out in a flooding manner, that is, using a large number of individuals, or inoculatively, with small quantities, aiming at efficient control and, at the same time, maintaining the pest at a level of biological equilibrium. During releases, the main considerations are the density of the ideal natural enemy for release and control, and the natural enemies' dispersion capacity. Temperature, precipitation and pesticide use conditions must be observed during release. Currently, the use of drones has boosted the release of natural enemies in large areas, with important results in pest control.

The cotton plant presents infestations of aphids, thrips and lepidopterans in the early stages of its phenology, which is an ideal time for the establishment of natural enemies such as T. pretiosum e C. external, via releases. This contributes decisively to the increase in populations of other natural enemies, such as ladybugs, syrphids, earwigs, predatory bugs, among others. This phase, which comprises the first 30 days after plant germination, should preferably not be the target of the use of synthetic insecticides.

The multiplication of natural enemies in biofactories has boosted biological control, which is a reality in Brazil. Its success has been increased mainly by the release of biological control agents by drones in cotton farming. Examples of successful application are the crops of producers associated with AMIPA (Associação Mineira dos Produtores de Algodão), with the release of T. pretiosum, a parasitoid of lepidopteran pest eggs. The partnership between Embrapa Cotton and AMIPA has generated technical information of great importance related to several natural enemies (T. pretiosum, C. external, C. grandis, B. vulgaris e E. annulipes) in relation to biofactory production and field use.

By Raul Porfirio de Almeida e Carlos Alberto Domingues da Silva, Embrapa Cotton

Article published in issue 286 of Cultivar Grandes Culturas Magazine