Among the citrus pests in the state of São Paulo, mites stand out, mainly due to the economic and environmental losses resulting from the need to apply synthetic acaricides. Some species of phytophagous mites have long been cited as important for the management of citrus farming, such as the leprosy mite, the false rust mite, the white mite and the purple mite. They attack various parts of plants, such as flowers, leaves, fruits at different stages of development, petioles, peduncles, branches and trunk. Furthermore, some species are vectors of viruses.
In Brazil, it is called citrus leprosy mite and in English literature as flat mites or false spider mite, species of the Tenuipalpidae family.
Brevipalpus yothersi is a polyphagous species, found on several host plants, including weeds common in citrus orchards, thus offering the possibility of serving as a refuge for the mite. This species is cosmopolitan, with reports on other continents, except the Arctic and Antarctic regions. In Brazil, it is found in several states of the Federation, in different species of the Citrus genus. In citrus plants, B. yothersi can be found throughout the year, with population peaks during the prolonged dry period, which in the state of São Paulo corresponds to the winter months. This mite has the ability to transmit the citrus leprosis virus. Brevipalpus papayensis is also found in citrus groves in São Paulo and can be recovered from various host plants, including weeds. Like B. yothersi, it is a cosmopolitan species. Its population in citrus groves is very low, however, this mite also has the ability to transmit the citrus leprosis virus.
Until recently, Brevipalpus phoenicis was considered the villain of history, identified as the main vector of citrus leprosis in the world and responsible for a large portion of the application of acaricides in Brazil. Now, it is known that the story is not like that, as B. phoenicis occurs in a very low population and it has not yet been possible to create it in the laboratory and prove whether it transmits the virus. Specimens of this mite have been found on a few plant species.
There is currently information on new species of Brevipalpus occurring in São Paulo's citrus industry. They will be duly published and publicized in the near future. These mites occur in larger populations on fruits than on leaves, especially those with wart symptoms.
The incidence of the leprosis virus causes severe fruit drop, death of branches and the plant, with a relatively low population capable of transmitting the disease. Pruning and removing symptomatic branches and especially early harvesting substantially helps control Brevipalpus. Infestation of harvested material helps spread these mites. The duration of the period from egg to adult of Brevipalpus is on average 35 days at 30ºC.
Popularly known as the false rust mite, the eriophyid Phyllocoptruta oleivora is reported as a key pest in citrus crops in Brazil and also in other countries. It presents host specificity, occurring in all citrus varieties. As an adult, it is yellowish in color, the body is fusiform, varying from 150µm to 165µm in length. Under favorable conditions, the complete cycle is around seven days to ten days in summer and 14 days in winter, with a longevity of around 20 days. The false rust mite can be found on leaves, branches and fruits and on the latter you can see the appearance of rusty spots that vary in intensity depending on the infestation. The wind greatly helps the spread of the rust mite. The greatest losses would be qualitative for the commercialization of the fruits and industrial performance.
Tegolophus brunneus was initially described in citrus plants collected in the state of São Paulo, in association with the false rust mite. Little is known about the actual damage caused by this mite on citrus plants. Currently, studies on the biology of this mite are being carried out. This species cannot yet be considered a pest for crops, until confirmatory studies are carried out. bud mite The eriophyid Aceria sheldoni is found in the buds that give rise to leaves and fruits, where they feed, causing deformations of these organs. This mite attacks several varieties of citrus, but causes more significant deformations in lemons.
Polyphagotarso nemuslatus is known as the white mite, due to its whitish color, or silver mite due to the damage caused to citrus fruits. This mite is polyphagous and cosmopolitan, being found on plants belonging to more than 60 different families. The white mite is found in all citrus varieties, mainly in acid lime orchards, such as the Tahiti lemon tree, occurring more intensely in rainy seasons and at the beginning of fruiting. The duration of the period from egg to adult is 3,7 days and longevity is 13 days.
Tetranychid mites may be of some importance in citrus orchards that present imbalances, caused by excessive application of fungicides, insecticides and water stress, or by inadequate management of spontaneous plants that serve as a refuge for predatory mites.
The tetranychid Panonychus citri can be found in almost all citrus growing regions of the world. These mites infest leaves, branches and fruits. On leaves and branches, symptoms are recognized by discolored spots, due to cell death, known as mottling. In severe infestations, the leaves become defoliated and dry. The cycle from egg to adult is completed in ten days to 11 days.
The tetranychid Aponychus chiavegatoi was described from specimens collected in citrus groves in the state of São Paulo. They are greenish-yellow mites with dark spots on the margin of the body. They live close to the ribs and do not produce webs. Apparently they do not cause significant damage to the crop.
Popularly known as the Mexican mite, Tetranychus mexicanus is frequently found in citrus crops. These are mites that range from orange-red to brownish-green due to the host plant and the part of the plant where it is found. It occurs mainly on younger leaves. Being considered a sporadic pest in citrus farming. The duration of the cycle from egg to adult is on average ten days to 12 days.
Eutetranychus banksi, known as the Texas mite, has a wide distribution on the American continent and is found on a wide range of host plants in Brazil. They generally do not constitute a pest for citrus crops, however, they can reach high levels in years of great drought. It is naturally controlled by entomopathogenic fungi. The duration of the cycle from egg to adult is on average 12 days to 13 days at 25ºC.
Brachytydeus formosa is found in large colonies on branches, peduncles and leaves. On the branches and peduncles, these mites cause the affected area to turn yellow. Yellow areas may appear on the leaves due to the attack of these mites. This species is found on a large number of host plants. In citrus cultivation, it occurs during the dry season of the year and is not considered a pest. The duration of the cycle from egg to adult is on average 37 days at 28ºC.
Predatory mites are also widely known in citrus groves. In São Paulo, the most common are Iphiseiodes zuluagai, Euseius citrifolius and Euseius concordis, all from the Phytoseiidae family. In addition to phytoseiids, predatory mites from the Stigmaeidae family have also been reported on citrus plants in São Paulo. Several studies demonstrate interactions between members of the Phytoseiidae and Stigmaeidae families and the potential for controlling phytophagous mites, as well as the effects of chemicals on these predators. In low populations, tetranychid and tideid mites serve as food for predatory mites.
The citrus agroecosystem is complex, lacking detailed studies on the diversity of mites and their interactions in different varieties and producing regions. In the state of São Paulo, citrus farming is carried out under different soil, climate and natural vegetation conditions, requiring scientific knowledge to conduct adequate and sustainable management. Recent information on the mite fauna demands new studies on the bioecology of these organisms in citrus farming. In view of the considerable increase in the application of agrochemicals in São Paulo's citrus industry, the impact resulting from the use of these molecules on phytophagous mites and natural enemies should be re-evaluated, especially regarding the effectiveness and registration of acaricides for Brevipalpus species. Due to the large number of pesticide applications in citrus farming to control insect and mite vectors, as well as other pests and diseases that limit production, it is necessary to constantly monitor pest resistance. It would also be relevant to consider the reduction of natural enemies resulting from the continuous application of chemical products and also the induction of these compounds to the phenomenon of hormesis, which would benefit phytophagous mites.
Jeferson Luiz de Carvalho Mineiro and Adalton Raga, Instituto Biológico
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