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The cerrado is a characteristic biome of the Brazilian territory and the species Caryocar brasiliense Camb. (Malpighiales: Caryocaraceae) is widely distributed among its regions (Ribeiro et al. 2018). Its fruits are used in human nutrition, production of cosmetics, lubricants and in pharmaceutical industry, and represent the main income source in many communities (Leite et al. 2020). According to collectors, leaves and fruits of this tree suffer damages caused by mites since they grow in isolated and deforested areas due to their protection by federal law. Despite the biological and social importance of C. brasiliense, there are few entomological studies with this species and its mites are unknown.
Diversity and abundance of mites can vary depending on the arrangement of branches on the tree and the parts of leaf. Some hypotheses explain these facts. Roda et al. (2012) noted that the arrangement of branches in the canopy of a tree affects the distribution of mites because the wind direction influences on the dispersion of this insect. On the other hand, Leite et al. (2017) pointed out that a greater exposure of foliage to the sun can influence on the quality of the tissues of the host plant together with the microclimate where they develop. Research carried out on other crops (Lemtur and Choudhary 2016) shows that mites generally prefer leaves and parts of the softer and thinner leaves of trichomes.
In this sense, the objective of this research was to study the spatial distribution of the population of mites in C. brasiliense trees grown in Brazilian cerrado areas for three years.
The study was performed in Montes Claros municipality, Minas Gerais state, Brazil, during 3 consecutive years (Jun 2011 through Jun 2014). This region has dry winters and rainy summers, and is classified as climate Aw: tropical savanna according to Köppen.
Three areas were used for data collection: strict sense cerrado (S 16º 44' 55.6" W 43º 55' 7.3", at 943 m asl), pasture, formerly cerrado vegetation (S 16º 46' 16.1" W 43º 57' 31.4" at 940 m asl) and campus of the Instituto de CiênciasAgrárias da Universidade Federal de Minas Gerais (ICA/UFMG) (16º40'54,5"S, 43º50'26,8"W, at 633m asl).
The design was completely randomized with 30 replicates (30 trees) - 10 adult trees (fruit production)/area. Treatments were: orientation of branches (North, South, West, and East), part of the canopy (apical, medium, and bottom parts of the tree), part of the leaf (distal, medium, and proximal part = near petiole), and leaf surface (adaxial and abaxial).
It walked (~600 m) in each area in a straight line, and every 50 m, randomly evaluated a C. brasiliense tree. Adult trees of C. brasiliense (producing fruits) were randomly sampled in each collection, except in the lawn of the university campus where trees were evaluated every time. Four expanded leaves, four flowers and four fruits from each stratum of the canopy (bottom, medium, and apical part) and from each cardinal orientation of branches (North, South, West, and East) of 30 trees were collected monthly (the morning) during each of the 3 years.
These plant materials were collocated in transparent white plastic bags, sealed and transported to the laboratory for counting of nymphs and adults (sum) of mites (phytophagous and predators). Counting started on average within 2 h after material collection, using a 12.5 X magnifying lens on leaves and flowers, but in fruits, mites were evaluated by direct counting (no lens).
Three fields in the central part (field equidistant between the principal vein and the margin) were counted from each leaf (adaxial and abaxial surface), but flowers were randomly distributed. In the case of fruit, mites present in the whole fruit were evaluated. These three fields were distributed one per each part of the leaf (distal, median, and proximal part = near petiole). These mites present in the evaluated parts (leaves, flowers, and fruits) of C. brasiliense were collected with brush and preserved in vials with 70% alcohol for identification by Dr. A.L. Matioli (several families) and Dr. Eddie A. Ueckermann (Agistemus).
The obtained data were subjected to normality test (Liliefors) and homogeneity of variance (Cochran and Bartlet) and, in the necessary cases, they were transformed according to √x + 0.5. Analysis of variance and mean comparison was performed with Tukey test (P <0.05).
No mites were observed on the flowers. The part of canopy of the tree and the orientation of branches did not influence on mite population in leaves and fruits. The highest amount of Histiostoma sp. (Histiostomidae)/cm2 (F = 6,588, P = 0.00213) was observed in the proximal part of the leaf (0.0593 ± 0.0082 A), without differing from the distal part (0.0288 ± 0.0047 B). In the medium part of the leaf, the number of Histiostoma sp. (Histiostomidae)/cm2 (0.0384 ± 0.0056 AB) was intermediate. The different parts of the leaf did not influence (P> 0.05) on the number/m2 of Acari sp. (0.000675 ± 0.00045), Agistemus sp. (Stigmaeidae) (0.00165 ± 0.0007), Eutetranychus sp. (Tetranychidae) (0.0001 ± 0.00005), Proctolaelaps sp. (Ascidae) (0.001275 ± 0.00085), Tetranychus sp.1 (Tetranychidae) (0.00215 ± 0.00145) and Tetranychus sp.2 (Tetranychidae) (0.00075 ± 0.0006).
Mite attack, preferentially, the proximal part of the leaf probably because this area is the newest, relative to other parts of the leaf (Maksymowych 1973) and consequently facilitates feeding and colonization by mites. Mites can prefer old leaves - Neoseiulus californicus (McGregor) (Phytoseiidae), Phytoseiulus persimilis Athias-Henriot (Phytoseiidae), and Tetranychus urticae (Koch) - or folded leaves and flower and fruit clusters - N. cucumeris (Oudemans), N. aurescens Athias-Henriot and Phytonemus pallidus (Banks) (Tarsonemidae) on Fragaria sp. (Rosaceae) (Fitzgerald et al. 2008).
The lack of relationship between the part of the canopy and the orientation of branches with the presence of mites on leaves and fruits in Caryocar brasiliense species can perhaps be explained by the uniform colonization niches in the canopy of this tree and by the low densities (in general) of these mites that did not allow to find any tendency. However, Roda et al. (2012) noted that medium stratum of a palm contained significantly more mites Raoiella indica Hirst (Acari: Tenuipalpidae) that fronds of the upper or lower canopy and fronds of the lower stratum, on average, had significantly less mites than the other two strat. Dichopelmus notus Keifer (Eriophyidae) showed a greater number of mature adaxial leaves in the lower and medium strata in Ilex paraguariensis St. Hil. (Aquifoliaceae) plants (De Gouvea et al. 2006).
Leaf surface affected mite population (table 1). The highest number of individuals/cm2 for the species Agistemus sp. (Stigmaeidae), Eutetranychus sp. (Tetranychidae), Histiostoma sp. (Histiostomidae), Proctolaelaps sp. (Ascidae), Tetranychus sp.1 and sp.2 (Tetranychidae) was observed on the abaxial leaf surface. The number of Acaridae was similar in both leaf surfaces.
Table 1 Number of mites (cm2) according to the leaf surface on Caryocar brasiliense. Montes Claros, Minas Gerais State, Brazil
| Mites | Leaf surface | F | P | |
|---|---|---|---|---|
| Adaxial | Abaxial | |||
| Acarin.s. | 0.0021±0.0007a | 0.0036±0.0009a | 1.560 | 0.21095 |
|
|
0.0027±0.0009b | 0.0115±0.0020 a | 15.349 | 0.00000 |
|
|
0.0000±0.0000b | 0.0011±0.0005a | 3.868 | 0.04747 |
|
|
0.0074±0.0018b | 0.1141±0.0104a | 153.759 | 0.00000 |
|
|
0.0010±0.0005b | 0.0093±0.0034a | 5.966 | 0.01274 |
|
|
0.0004±0.0003b | 0.0165±0.0028a | 33.240 | 0.00000 |
|
|
0.0018±0.0008b | 0.0047±0.0012a | 4.096 | 0.04122 |
Means followed by the same letter (average ± SE) in the line are not different by the test of Tukey (* P< 0.01 and ** P < 0.05). n.s. =no significant by ANOVA.
This preference (abaxial surface) is commonly reported to mite and is due to more protection against climatic elements (i.e. rainfall) and this surface is more tender, which favors mite feeding (Sudo and Osakabe 2011). Agistemus sp., Euseius concordis (Chant) (Phytoseiidae) and Iphiseiodes zuluagai Denmark & Muma (Phytoseiidae) occurred on the inferior face of the leaves of I. paraguariensis (De Gouvea et al. 2006). Moreover, leaf surfaces with hairiness and roughness can negatively affect mites, including the predators as Agistemus exsertus Gonzalez (Acari: Stigmaeidae), on Althaea rosea L. (Malvacea) and Morus alba L. (Moraceae) plants (Saber and Rasmy 2010).
It is suggested, as preliminary sampling plan for mites (phytophagous and predator) on C. brasiliense leaf, to assess 1cm2 (pocket magnifying lens) in the proximal region (near petiole) of the abaxial surface of leaf in four leaves/plant, all leaves in the basal region of the plant (greater ease in sampling), in 10 plants per plot (1,000 plants/plot).
