Cotton aphid and its natural enemies

The aphid Aphis gossypii It is one of the key pests of cotton crops. Although it is polyphagous, having more than 80 species of plants as hosts, the insect finds cotton as a suitable food both for its nutritional aspect and for its great availability in the agricultural environment of the Brazilian Cerrado. In the climatic conditions of this biome, characterized by high temperatures and common occurrences of drought throughout the cotton crop cycle, the species has high reproductive potential, a high rate of population increase and a high speed of dispersal.

The reproduction capacity of these insects is enormous, as it occurs through thelytotic parthenogenesis, that is, females are produced from unfertilized eggs, excluding the need for males to mate.

Aphid as a bioindicator

When at low incidence, aphids are an important bioindicator, as they can provide parameters for evaluating the environmental quality of the crop. As it serves as food for several natural enemies, its presence in low numbers indicates the possibility of maintaining beneficial species, which control it and other important crop pests.

The aphid will only be a pest when at high population density it causes stress to the plant due to excessive sap sucking and compromising the photosynthesis process; or when its excretion causes caramelized cotton. Therefore, the level of aphid control on cotton plants is established in up to 70% of plants with the presence of colonies (more than three aphids per leaf) when dealing with cultivars resistant to vein mosaic. Otherwise, in susceptible cultivars, the control level drops to 10% of plants with the presence of colonies.

Natural and applied biological control

Among the aphid's natural enemies, there are several species of predators, parasitoids and entomopathogenic microorganisms. Some are naturally occurring, needing to be conserved in agricultural environments, others are released by flooding (large number of individuals at once to quickly reduce the pest, without expectation of continuous effect), others released by inoculation (small number of individuals, released one or more times, with the intention of multiplying in the environment).

Parasitoids and predators

• Lysiphlebus testaceipes (Hymenoptera: Aphididae): wasps that parasitize aphids, nymphs or adults, wingless or winged. When they develop inside their host's body, they transform the aphid's body into mummies. They have high reproductive capacity, short generation time, good dispersal capacity and a life cycle synchronized with that of aphids.

• Aphelinus gossypii (Hymenoptera: Aphelinidae): aphid parasitoids, measuring 3 mm and black in color. Like Lysiphlebus, its parasitism promotes the mummification of aphids.

• Aphidius platensis (Hymenoptera: Braconidae): solitary endoparasitoid of aphids, marketed for the control of aphids in protected crops in Europe. In Brazil, it was introduced in the Southern Region of Brazil, to control aphids in wheat crops. The parasitoid also uses cotton aphids to multiply its descendants.

• geocoris sp. (Hemiptera: Geocoridae): frequently found naturally in cotton crops, they prey on aphids, mites, whiteflies, coleloptera, eggs and larvae of lepidoptera and stink bug nymphs. In North America, these insects are already commercialized for inoculative release.

• Orius insidiosus (Hemiptera: Anthocoridae): known as the pirate bug, it is a voracious predator of aphids that occur on cucurbits, ornamental plants and cotton. These bedbugs have excellent search behavior and their multiplication capacity is high when there is good prey availability. Even in adverse conditions, they are resilient and maintain a low population density. In cotton, aphid predation is frequent, but they also attack thrips, eggs and first and second instar caterpillars of several species. This biological control agent is already sold in Brazil.

• Cycloneda sanguineae Coleomegilla maculata (Coleoptera: Coccinellidae): highly efficient predatory ladybugs, they prey on aphids with great efficiency. They have high biotic potential, excellent search and predation capacity in the larval and adult stages, in addition to being possible to establish mass breeding in the laboratory. Ladybugs are available for sale on the Brazilian market.

• Chrysoperla externa (Neuroptera: Chrysopidae): known as garbage bugs, they are polyphagous predators and feed on several species of economic importance, such as eggs and newborn caterpillars, mealybugs, mites, although they have a preference for aphids. Due to these characteristics, in addition to the ease of creation, they are used in biological control applied through mass releases.

• Polistes sp. (Hymenoptera: Vespidae): these species prey on aphids at different stages of development. However, as generalists, they prey on other agricultural pests, such as caterpillars and other suckers, in addition to aphids, in constant search for alternative prey, exploring the entire environment (high foraging capacity), with the peculiarity of being able to feed several times on prey previously attacked, thus acting as optional experts.

• Doru luteips (Dermaptera: Forgiculidae) and Euborellia annulipes (Dermaptera: Anisolabididae): known as earwigs, as they have a pair of pincer-shaped cerci at the apex of the abdomen, these species live in humid and shaded places among plant debris. They have nocturnal habits and are promising in the biological control of cotton aphids, as they have predatory behavior towards the pest.

• Toxomerus sp. (Diptera: Syrphidae): genus of predators with abundant species in Brazilian crops. Commonly known as “mindim”, in their larval stage they are voracious predators of aphids, whiteflies, leafhoppers and thrips.

Entomopathogenic fungi

Entomopathogenic fungi cause infection due to the germination of their spores when penetrated into the insect's cuticle through enzymatic hydrolysis. Entomopathogenic fungi produce a large amount of polymer-degrading enzymes from the insect cuticle, converting the insect's tissues into nutrients for its growth.

• Cordyceps sp: (=Isaria) genus of entomopathogenic fungi that contain many species that can infect different orders of insects at all stages of development. It grows quickly and colonizes the host with its white mycelium, which can change to pink or purple. Some isolates of this fungus are more effective against a specific insect; other isolates are capable of infecting a large proportion of insects and mites.

• Metarhikum anisopliae: due to its high efficiency and ease of production, it is one of the most produced and used fungi in agriculture. It is an agent for controlling important pests, such as the grasshopper in sugar cane. This fungus is produced by several companies in Brazil to be used to control various pests, including the cotton aphid.

Trends in the use of bioinputs

Biological control of aphids is especially interesting, as it can eliminate the need for chemical control in critical phases of the plant's development, when its root system is not yet fully established (initial phase, 20 to 50 days after emergence) or when the bolls are open.

The obstacles to mass breeding, commercial production and marketing itself are being overcome by companies producing bio-inputs and the demand for these products is on the rise. This reflects a paradigm shift, with producers seeking alternative tools to chemical pest control. This trend should contribute to reducing the number of applications in cotton cultivation, with consequent environmental gains and ensuring the profitability of the crop.

By José Ednilson Miranda, Bruna Mendes Diniz Tripode, Valéria de Lima Jardim, Cherre Sade Bezerra da Silva, Embrapa Cotton; Eliane Dias Quintela, Embrapa Rice and Beans

Article published in issue 289 of Cultivar Grandes Culturas magazine