Distribution, abundance and seasonality of scale insects in sugarcane crops in the state of São Paulo

Abstract In the state of São Paulo, the main sugarcane producing region of the world, two species of scale insects have frequently occurred, Aclerda takahashii (Kuwana, 1932) (Hemiptera: Aclerdidae) and Saccharicoccus sacchari (Cockerell, 1895) (Hemiptera: Pseudococcidae). To map the distribution and abundance of these species, 17 sugarcane producing fields, distributed in six mesoregions in São Paulo, were evaluated in August 2017 and, January, February, June and July 2018 during the ripening phase. The study on the seasonality of these species, by the presence or absence of the scale insects during the phenological cycle of the plant, was conducted between August 2017 and July 2018 in two sugarcane producing fields in the municipality of Jaboticabal, São Paulo, Brazil. The presence of S. sacchari was found in all the analyzed locations, and A. takahashii in twelve. Both scale insects showed significant difference of infestation in the node’s region of the stems during the ripening phase in one of the studied locations. The aclerdid presented significant difference by infestation in one site during the ripening phase of the plant. The pseudococcid infested a greater number of nodes in the following phases of development; vegetative, grand growth and ripening in both studied areas, but it was in one site during the ripening phase that presented the greatest difference. Although the pink sugarcane mealybug was more abundant than A. takahashii in both studies, there were no patterns of relationships between the numbers of individuals to geographical locations and temperature.


Introduction
In Brazil 18 species of scale insects associated to sugarcane were reported, of which Aclerda takahashii (Kuwana, 1932)
Probably due to its greater distribution in the globe, S. sacchari has been better studied in relation to bioecological aspects, as well as its impacts on sugarcane fields (Atiqui and Murad, 1992;Mohamed et al., 2009;Victoria et al., 2005;Zhang et al., 2018).The population dynamics of this insect was studied in Australia during a five-year period, 1999 to 2003 (Bonnett and Hewitt, 2005).These authors found that in the months of January and February, corresponding to the end of summer, there were greater population peaks, varying from one year to another, and among the different studied sites.Bonnett and Hewitt (2005) attributed these irregularities to climatic conditions, the warmer months, and to different agricultural practices in the studied regions.
Knowledge about the occurrence and distribution of pest species in a given geographical location is of great importance, as legal measures can be taken to prevent their transport to free areas of these organisms.However, studies on its seasonality and population density, in a given region, are fundamental for the establishment of action related to integrated pest management.
Therefore, this study analyzed the distribution and abundance of A. takahashii and S. sacchari in sugarcane plants in the ripening phase in the state of São Paulo, and the seasonality of both species by the presence of them in all phenological phases in two sites in Jaboticabal, São Paulo, Brazil.
In South America, A. takahashii is restricted to Brazil, where was first reported in the state of São Paulo, in 1932 (Silva et al., 1968), the largest sugarcane producer in the world (Embrapa, 2020).Later it was spread to the states of Pernambuco, Alagoas, Espírito Santo, Rio de Janeiro and Rio Grande do Sul and in the Federal District (Oliz and Wolff, 2014;Morales et al., 2016).
Under laboratory conditions, the pseudococcid has four to five generations per year; with shorter life cycles when reared at 20 °C (Kalra and Sidhu, 1964).In India, its presence in sugarcane slowed the growth of the plant, and caused the death of newly planted sheets (Yakoub, 2012).This insect can also cause a reduction in stem diameter and weight, and reduction in sugar by up to 21%, in addition to acting as a vector for the bacilliform sugarcane virus (BSCV) (Atiqui and Murad, 1992;Mohamed et al., 2009;Victoria et al., 2005).
Aclerda takahashii and S. sacchari preferentially infest the region nodes of the stem, under the leaf sheath (Bonnett and Hewitt, 2005;Stocks, 2016).In addition, the pseudococcid can infest the roots (Kalra and Sidhu, 1964;Inkerman et al., 1986;Bonnett and Hewitt, 2005).Inkerman et al. (1986) described that the nymphs reach the aerial part of the plant, after their sprouting, settling in the region nodes under the sheaths.
Due to this cryptic habit, scale insects are rarely dispersed through wind or water, and their control becomes difficult (Rajendra, 1974;Inkerman et al., 1986 For the seasonality study, monthly collections of scale insects were made between August 2017 and July 2018, in two sugarcane producing fields, located in the municipality of Jaboticabal, São Paulo, Brazil, followed by the coordinates; (site 1) -21°13´22´´ S, -48°16´81´´ W, altitude of 608 m, and (site 2) -21°17´31´´ S, -48°18´63´´ W, altitude of 614 m.All phenological phases of the plant, under the same clumps, were evaluated.

Experimental design
To dimension the species in the sugarcane producing fields in the state of São Paulo, an adapted technique described by Bonnett and Hewitt (2005) was used.Ten sugarcane plants from the edge of the crop, cultivar RB86 7515, five meters apart from each other, were randomly selected and evaluated.The leaves were tilted until the stem area was exposed, making it possible to observe the individuals with the naked eye.The nodes of the stem infested by scales insects were counted, observing the presence or absence of A. takahashii and S. sacchari, in the phases of the third instar nymph and adult.
For the evaluation of the statistical analysis, the data were submitted in completely randomized design (CRD) with 17 treatments and 10 replicates for the analysis of distribution and abundance of scale insects in the sugarcane producing fields on ripening phase distributed in the state of São Paulo, Brazil, and 12 treatments and 10 replicates for the analysis of the seasonality of scale insects in all phenological phases of the plants in each site in the municipality of Jaboticabal, São Paulo, Brazil, for each species.The program used was SAS ® University Edition, version 9.4.The data, number of nodes infested with scale insects were submitted to Bartlett´s tests to verify homocedasticity (PROC GLM) and Cramer von Mises´s test for normality (PROC UNIVARIATE).The data showed normality in this way the Analysis of Variance (PROC ANOVA) was conducted.The means (PROC MEANS) when significant were compared using the Tukey test (p < 0.05) (Everitt and Hothorn, 2005).

Identification and deposit of voucher species
To confirm the species, samples were collected in the field and mounted on permanent slides using the technique described by Willink (1990).The identification took place under an optical microscope through morphological characteristics using the works of McConnell (1954) for A. takahashii and Williams and Willink (1992) for S. sacchari.
The voucher species were deposited in the Reference Collection of Insects and Mites (CRIA) of the Department of Agricultural Production Sciences of the FCAV/UNESP, Jaboticabal, São Paulo, Brazil.

Distribution and abundance of Aclerda takahashii and Saccharicoccus sacchari
Saccharicoccus sacchari was best distributed, being present in all locations in the state of São Paulo, while A. takahashii was observed in 12 (see Figure 1).
Regarding the abundance of species in the evaluated sugarcane producing fields, A. takahashii infested 2.6 nodes in São Carlos, providing statistical difference for the other locations that did not differ from each other (as shown in Table 1).
The population of Saccharicoccus sacchari differed in high incidence in Votuporanga, infesting 3.0 nodes of the analyzed plants (as shown in Table 1).

Seasonality of Aclerda takahashii and Saccharicoccus sacchari
Regarding the two analyzed sugarcane producing fields in Jaboticabal, the population of A. takahashii was more abundant in site 1, in March 2018, ripening phase (see Figure 2).The aclerdid infested 0.5 nodes of the plants, with a significant difference for the other analyzes that did not differ from each other (as shown in Table 2).
The pseudococcid was more abundant in site 2 in August 2017, ripening phase (see Figure 3).Saccharicoccus   Biogeography of scale insects sacchari infested 2.6 nodes, but there were no significant differences among analyzes (as shown in Table 2).

Discussion
Saccharicoccus sacchari was found to be better distributed and infesting more nodes in the sugarcane fields in the state of São Paulo compared to A. takahashii.Although the aclerdid was registered in a few locations as to the pseudococcid, it was at least found in one location in each geopolitical mesoregion in the state of São Paulo.
The wider distribution and quantity of infested nodes found for S. sacchari in relation to A. takahashii may be related mainly to its more efficient dispersion.The pseudococcid can survive on newly-planted and/or cut sheets, having been observed infesting sheets at a depth of 30 centimeters (Sartiami et al., 2017).These, before migrating to the aerial part of the plants, can also infest the roots; whereas A. takahashii has been observed only in the node's regions, in the aerial part of Saccharum spp.(Oliz and Wolff, 2014).In addition, S. sacchari apparently produces more honeydew than A. takahashii, probably attracting a greater number of protective ants against natural enemies.However, for both species Cruz et al. (2019) found a significant number of associated natural enemies, ten for A. takahashii and 12 for S. sacchari.
As for the seasonality of the two species in the municipality of Jaboticabal, São Paulo, Brazil, the most abundantly recorded specimens show an appearance pattern at the phenological phases of the plants.In site 1, the aclerdid was more present in the month of March 2018, referring to the phenological phase of ripening, and in site 2, there was no significant difference in appearance, however its greatest record was found in the same period, however plants in the intermediate phenological phase of grand growth.In turn, the pink sugarcane mealybug on site 1, infested more nodes in the months of September and October 2017, with plants referring to the initial phenological phase of grand growth, while on site 2, its greatest record was in the final phenological phase of ripening, preceding the harvest.According to INMET (2018) the sugarcane producing fields of Jaboticabal presented, at the time of analysis, precipitation 0 mm, and average temperature of; 15.6 °C, 16.6 °C, 20.0 °C and 19.4 °C, consecutively for the months of August, September and October 2017 and March 2018.Although there is no information on the optimal temperature for the development of A. takahashii, however S. sacchari, according to Kalra and Sidhu (1964), the optimal reproduction temperature of the species is 20 °C, which may have favored its registration in these locations.However, studies conducted by Bonnett and Hewitt (2005) in Australia did not demonstrate a seasonal distribution relationship, as it was registered that although in summer, the warmest period of the year, which was expected to have the largest population peaks, similar to what was observed in this study, populations of both lower species in relation to the months of December 2017 and January and February 2018.During this period, the rains probably may have influenced the population dynamics of this species, since the plant accumulates water in the sheath, causing the scale insects to be killed by being immersed part of the time, or by the action of entomopathogenic fungi that are favored due to the high humidity.According to Mora-Lugo et al. (2015), entomopathogenic fungi as those of the genus Aspergillus are easily found in natural environments, and these infect scale insects, causing their death.However, the study does not present a relation of population dynamics of the species, favored or not by precipitation and average temperature.
Aclerda takahashii and S. sacchari are widely distributed in the state of São Paulo, and although the pseudococcid has infested more nodes in the stems than the aclerdid, in both studies, there were no population dynamics relationships of both species to geographical locations and temperature.

Figure 2 .
Figure 2. Infested nodes for both species in the site 1 in the phenological of sugarcane plants.

Figure 3 .
Figure 3. Infested nodes for both species in the site 2 in the phenological of sugarcane plants.

Table 1 .
Infested nodes with scale insects, by locations in the state of São Paulo, Brazil, in the ripening phase.

Table 2 .
Infested nodes with scale insects, by sites in the municipality of Jaboticabal, São Paulo, Brazil.