Expanded presence: new whitefly species identified

A recent study demonstrated that there are at least three species of whitefly in Brazil: Middle East-Asia Minor 1 - MEAM1 (new classification), also known as biotype B, New World 1 (NW1) and New Wolrd 2 (NW2). The Meam1 species was introduced in Brazil in the 90s, possibly through the exchange of ornamental plants colonized by the insect, and is currently widespread in practically all agricultural regions of the country, causing major losses related to the insect. All research on whiteflies carried out in the country has always taken into account only this species.

Species NW1 and NW2, apparently, are native to the Americas. NW2 is frequently found in wild peanuts (Euphorbia heterophylla), a very common weed in the field and which is generally infected by begomovirus. This is the first record of its existence in Brazil. Also found in Argentina, it is present in several locations in São Paulo and also in Alagoas.

The New World 1 species was found colonizing jiló (Solanum gilo) and viola-corda (Ipomoea sp.), only in the regions of Registro, Iguape and Ilha Comprida, in São Paulo. It is estimated that the species did not disappear due to the relative geographic isolation of these locations in relation to other agricultural areas in São Paulo. It is possible that New World 1 is the species that existed in Brazil before the entry of Biotype B. However, as there is no preserved material from that time, this is just an assumption. In Alagoas, interestingly this species was found on tomato plants.

The discovery of these two species in Brazil caused surprise, as it was believed that, after the introduction of the whitefly Biotype B (MEAM1) into the country, the previously existing species would have been replaced or even extinct. Although the NW1 and NW2 species are found in a smaller number of individuals compared to the MEAM1 species, several works are underway to study their role as virus transmitters, since these species are found more frequently in weeds and could transmit the weed viruses for cultivated plants, contributing to the epidemiology of diseases transmitted by whiteflies. Weeds are an important reservoir of viruses in nature and often act as a source of inoculum for viruses found in cultivated plants.

How to manage

Unfortunately, due to the rapid biological cycle of the whitefly and its high reproductive capacity, its control is greatly compromised in the presence of large populations of the insect. Constant monitoring of the population and management immediately after its arrival in the planting area, using recommended and registered insecticides that act on all stages of the insect, can guarantee successful control. Furthermore, insecticides from different chemical groups should be alternated, reducing the risk of resistant insect populations emerging. Avoid staggered plantings of the crop (new plantings next to older plantings), eliminate weeds in and around the crop, hosts of whiteflies and sources of viruses, never abandon the crop at the end of the cycle and preferably destroy everything else after the final harvest, are examples of measures to be adopted in a management program against whiteflies and to combat viruses transmitted by the insect.  

It is important to monitor whitefly species in different regions of Brazil, as Europe has major problems related to the whitefly species known as MED, which is characterized by rapidly acquiring resistance to the main insecticides used in agriculture. This species has not yet been reported in Brazil and it is expected that it will not even be found on Brazilian soil, as it could cause even greater losses related to this insect in the country.

Distribution and attack

Bemisia tabaci (Hemiptera: Aleyrodidae), also known as whitefly, is today considered one of the main agricultural pests. In recent years, a large population increase of this insect has been observed in different agricultural systems. This fact has left producers concerned not only due to the damage potential of this pest, but mainly due to the difficulty and high cost of control. The increase in whitefly populations appears to be related to the presence of host crops throughout the year and also to the indiscriminate use of non-selective insecticides in production systems.

In Brazil, its main targets are tomatoes, beans, melons and potatoes. In addition to these crops, soybeans, pumpkins, watermelons, various vegetables and ornamental plants have also been affected. In most of these crops, high whitefly infestation can cause direct and indirect damage. Direct damage to plants occurs due to their feeding (sap sucking and injection of toxins), reduction of plant vigor and induction of physiological anomalies, such as irregular fruit ripening and silvering of pumpkin leaves. The whitefly also deposits a large amount of sugary secretion on leaves, which harms the plant's physiological processes and favors the occurrence of sooty mold.

However, its insidious action is due to the fact that the whitefly is capable of transmitting more than 200 species of viruses, most of which have a significant economic impact on vegetable production. These viruses belong to different genera such as Begomovirus (family Geminiviridae), Crinivirus (Closteroviridae), Carlavirus (Betaflexiviridae) and Ipomovirus (Potyviridae). Begomoviruses and Criniviruses are currently considered the most important limiters of tomato production, in addition to their incidence having also been observed in crops such as peppers and potatoes.

Whiteflies are sucking insects that feed on the phloem of plants, both in the immature phase (nymphs) and in the adult phase. These insects measure around one millimeter to two millimeters, adults have a pale yellow back and white wings. Although called a whitefly, it is not a fly, that is, it is not a dipteran. As its wings cover almost its entire body, white becomes the predominant color, hence the name given to it.

Like other insects, their life cycle comprises four phases (egg, nymph, pupa and adult) and is influenced by climatic and environmental conditions, mainly temperature, relative humidity and the greater or lesser abundance and susceptibility of plants. hostesses. Under conditions that are favorable to it, with a temperature of around 28°C and a relative humidity of 70%, the MEAM1 species can have 11 to 15 generations per year (each female laying 100 to 300 eggs during her cycle of life).

The whitefly is found in the tropics and subtropics of all continents. It is believed to have emerged in Asia and spread throughout Europe, Africa and the Americas through human action, through the dissemination of contaminated plant material. B. tabaci is a complex of different species, morphologically indistinguishable. There are at least 29 species described in the world. To differentiate them, molecular techniques are used, such as sequencing the insect's mitochondrial cytochroma oxidase I (mtCOI) gene and comparison with known mtCOI sequences.

Click here to read the article in issue 80 of Cultivar Hortaliças e Frutas.