Integrated whitefly management in corn

A host previously considered unlikely, over the last few years corn has also started to harbor whitefly infestations, Bemisia tobaccoi, biotype B, which represents a potential threat to other commercial grass species, such as sorghum, grass brachiaria and sugar cane, cultivated extensively in Brazil. Strategies adopted in an integrated manner are the way to adequately manage this cosmopolitan pest, with the capacity to feed on more than 600 species of plants.

The whitefly bemisia tabaci belongs to a complex of morphologically similar species, which are in constant evolution. In Brazil, at least four species of B. tabaci are present: Middle East Asia Minor 1 - MEAM1 (biotype B), Novo Mundo and Novo Mundo 2 (biotype A). The Mediterranean whitefly - MED (biotype Q) was observed in 2013 in Rio Grande do Sul, with no reports yet of its spread to other regions of Brazil. The Q biotype is resistant to neonicotinoid and juvenoid insecticides and also transmits virus species that are not present in Brazil, such as ToTV (roasted tomato virus) and TYLCV (yellow tomato leaf curl virus), important viral diseases in tomatoes in countries that the Q biotype occurs. This new biotype collected in Brazil could change the current scenario of virus species predominant in the country.

A B. tabaci It was described more than 100 years ago, and has since become one of the world's most important pests in tropical and subtropical agriculture, as well as in protected cultivation. It easily adapts to new host plants and geographic regions, having been observed on all continents, except Antarctica. The international transport of plant material and people, as well as the increase in production and agricultural areas, has contributed to the geographic spread of this species.

In Brazil, before the introduction of biotype B in 1991, B. tabaci it was an important pest only of beans as a vector of the bean golden mosaic virus. After its introduction, the spread and increase in population size of biotype B were favored by Brazil's agricultural cultivation system. This cosmopolitan pest feeds on more than 600 plant species and the range of host plants has increased over time, which has been attributed, among other reasons, to the use of irrigated monoculture agricultural practices. This large number of hosts has allowed the whitefly to reproduce and migrate rapidly on both wild and cultivated hosts such as cotton, soybeans, tomatoes, beans, potatoes, melons, etc., often reaching extremely high population sizes. Whitefly “clouds” have been observed in Ceará, Bahia, Rio Grande do Norte, Paraná, Mato Grosso and Goiás, causing losses ranging from 30% to 100% in several crops. Additionally, due to the tropical climate and long growing season, a second corn crop, known as "safrinha", is planted in February, immediately following the soybean or bean harvest planted during October and November each year. This agricultural system has favored the reproduction of biotype B in corn over the last three or four years, a until recently unlikely host for this pest (Figure 1). The demonstrated ability of biotype B to B. tabaci Completing its life cycle in corn has implications for other tropical agricultural systems around the world, where corn is grown as a major crop for animal and human food and biofuel production. The colonization of corn by biotype B of B. tabaci is a potential threat to other commercial grass species, including sorghum, grass brachiaria and sugar cane, which are cultivated extensively in Brazil.

Excessive losses in the production of grains, vegetables and ornamental plants due to B. tabaci Biotype B has been observed worldwide. Losses are due to the transmission of viruses (more than 150 species), direct damage due to the feeding of phloem sap, which causes physiological disturbances in the plant, and the excretion of a sugary substance that favors the growth of fungi on the leaves (fumagin).

The main method of controlling whiteflies continues to be the use of synthetic insecticides, which are applied several times throughout the year, on different crops. Several insecticides, despite being sold under different names, are made up of the same active ingredients. The insecticides most used to control whiteflies are neonicotinoids, mixtures of neonicotinoids + pyrethroids and growth regulators (juvenoids and chitin synthesis inhibitors), which has resulted in a reduction in efficiency and power. residual.

No control strategy, when used in isolation, has been demonstrated to be effective for managing whiteflies and the viruses that this insect transmits. Control measures must be initiated before sowing and must be planned in such a way that the whitefly population is kept low, as, once out of control, it is unlikely that any measure used will have a satisfactory result.

Table: management strategies to prevent the multiplication of insects and virus-infected plants

Embrapa, with the support of several institutions (Agriculture departments, universities, rural extension agencies, cooperatives, rural unions, etc.) has concentrated efforts so that the various whitefly and virus management actions that are being planned can be available to the production sector. Actions to train multipliers are being intensified with a view to encouraging greater adoption of integrated pest management (identification of pests and natural enemies, management of insect resistance to insecticides, product application technology, crop rotation, biological control, etc.) in the agricultural production system. The goal is to implement these methods through joint actions with the community, including educational and extension activities.

Eliane D. Quintela, Embrapa Rice and Beans

Article published in issue 195 of Cultivar Grandes Culturas.