Researchers find two species of whitefly native to the Americas

The insect is one of the most feared plagues of the tomato, bean, melon and potato.

By José Tadeu Arantes

Agência FAPESP – In Brazil, the expression “white fly” means an extremely rare and generally auspicious event. For farmers, however, a whitefly means something entirely different: It is a common insect that is a nightmare for producers of fruits, vegetables, ornamental plants and other crops. When the whitefly feeds on its host plant’s stalk, it reduces the plant’s vitality and induces physiological anomalies.

“The whitefly deposits large quantities of sugary secretions, which lead to the growth of fungi that impede photosynthesis and thus affect the growth of the plant, reducing its productivity,” commented Professor Renate Krause Sakate, from the Department of Vegetable Production at Universidade Estadual Paulista’s School of Agronomic Sciences (FCA-Unesp), Botacatu campus.

“In addition to these issues, the whitefly transmits viruses, including the Begomoviruses and the Criniviruses, which can limit the growth of vegetable plants such as tomatoes,” he said.

Krause Sakate and his team — which includes Professor Marcelo Agenor Pavan and researcher Valdir A. Yuki, of the Agronomics Institute (IAC), along with several master’s students — concluded a study funded by FAPESP. In this study, they found two potentially native species of the insect in the state of São Paulo, named New World 1 and New World 2.

The discovery was unexpected because it had been thought that the invasive B Biotype whitefly (Middle East-Asia Minor 1, MEAM1) had largely replaced the species that previously existed or even driven them to extinction.

“MEAM1, which arrived in the country in the 1990s, is highly invasive. In several parts of the world, its arrival caused the extinction of local species. However, in our study, we verified the existence of the New World 1 and New World 2 species in São Paulo, Mato Grosso do Sul and Alagoas. Now, we want to understand their role in the transmission of the virus associated with whitefly,” explained Krause Sakate.

The study, which also involved collaboration with researchers Enrique Moriones and Jesus Navas-Castillo of the Spanish National Research Council (in La Mayora, Spain), was recently published in the Journal of Applied Entomology, a high-impact journal in this field.

With the scientific name of Bemisia tabaci, the whitefly measures 1 to 2 millimeters in length. The adults have pale yellow backs and white wings. Because the wings cover almost their entire body, they appear to be predominantly white, explaining the name given to the insect.

Like other insects, the whitefly has a life cycle that consists of four phases (eggs, nymph, pupa and adult) and is influenced by climatic and environmental conditions, mainly temperature, relative humidity and the abundance and susceptibility of host plants. 

 Under the right conditions, with temperatures of approximately 28°C and a relative humidity of 70%, MEAM1, which is more vigorous than the New World I and the New World II, could produce 11 to 15 generations per year, with each female laying 100 to 300 eggs during its life cycle.

The whitefly is found in tropical and subtropical regions on every continent. It is believed to have emerged in Asia and spread to Europe, Africa and the Americas through human activities, mainly via contaminated vegetable material. In Brazil, its main victims are tomatoes, beans, melons and potatoes, but it also affects soybeans, pumpkins, watermelons and other vegetables and ornamental plants. 

The whitefly is particularly insidious because it is capable of transmitting more than 200 types of virus, the majority of which have a significant economic impact on the production of fruit and vegetables.

“The begomoviruses, which are some of the major viruses transmitted by MEAM1, are currently the pests with the greatest negative effect on tomato production, and they have also been found to impact bell pepper and potato crops. They cause reduced growth, physiological changes and the production of shrunken fruit with irregular maturation,” said Krause Sakate.

It is important to consider that the epidemiological distribution of the whitefly is related to certain aspects of modern agriculture, such as the expansion of monoculture and the increasing utilization of agrotoxins, in addition to the insect’s ability to adapt to several hosts. The first account of Bemisia tabaci in Brazil was in 1928; however, they were likely present well before this date. 

Older species?

MEAM1 is the predominant whitefly species in Brazil, and it is found in both crop growing areas and in wild plant life. Until recently, studies of the whitefly in Brazil only considered this species.

In the new study, however, a broad survey was conducted in more than 40 municipalities in São Paulo and 13 municipalities in Alagoas State. Using a highly sensitive and specific test, the scientists discovered the New World 1 and New World 2 species. 

The New World 1 species was found colonizing Scarlet eggplant (Solanum gilo) and morning glory (Ipomoea sp.) plants in the regions of Registro, Iguape and Ilha Comprida in São Paulo State. The researchers predict that the species is unlikely to disappear by virtue of the relative geographical isolation of these locations from other São Paulo farming areas.

“It is possible that New World 1 is the species that existed in Brazil before the B Biotype [whitefly] was introduced, but because there is no material preserved from this time, this is only a hypothesis,” said Krause Sakate. In Alagoas State, this species was found on tomato plants.

The New World 2 species was frequently found on the Mexican fire plant (Euphorbia heterophylla), a weed that is common in the field and that is generally infected by Begomovirus. This is the first record of the existence of New World 2 in Brazil. Also found in Argentina, it is also present in several locations in the São Paulo and Alagoas state.

One unexpected finding was that the two supposedly older species were present even in plants colonized by MEAM1, indicating that several species of whitefly can occupy the same ecological niche. However, the New World 1 and New World 2 species were always less abundant than MEAM1 and their roles as virus transmitters, particularly for Begomovirus, remain unknown. 

The establishment of this role is the focus of ongoing research by master’s student and FAPESP fellow Bruno Rossitto de Marchi, who is supervised by Krause Sakate.

“We isolated colonies of the New World 2 species, supposedly the oldest [species in Brazil], and infected them with Begomovirus; now, we are following their day-to-day life in relation to host plants to determine whether the species is or is not a virus transmitter,” said Krause Sakate.