Geographical distribution of genetically determined types of Nezara viridula (L.) (Heteroptera: pentatomidae) in Brazil

Distribuição geográfica de tipos geneticamente determinados de Nezara viridula (L.) (Heteroptera: Pentatomidae) no Brasil

ECOLOGY, BEHAVIOR AND BIONOMICS

Geographical distribution of genetically determined types of Nezara viridula (L.) (Heteroptera: pentatomidae) in Brazil

Distribuição geográfica de tipos geneticamente determinados de Nezara viridula (L.) (Heteroptera: Pentatomidae) no Brasil

Lúcia M. Vivan^I; Antônio R. Panizzi^II

^IDepto. Zoologia, Univ. Federal do Paraná, C. postal 19020, 81531-990, Curitiba, PR. Present address: Fundação de Apoio à Pesquisa Agropecuária de Mato Grosso, C. postal 79, 78750-330, Rondonópolis, MT

^IIEmpresa Brasileira de Pesquisa Agropecuária, Embrapa - Soja, C. postal 231, 86001-970, Londrina, PR [e-mail]

ABSTRACT

Nezara viridula (L.) is a cosmopolitan and polymorphic pentatomid. Several genetically determined types have been described due to body color variation in adults. A survey covering 13 Brazilian states was conducted during 2001 and 2002 to determine the geographical distribution of the main types. Type G (smaragdula - body entirely green), the most common, showed a wide distribution, from south to north (latitude 2º 49' N to 31º 46' S), except in the Central-West Region. Type O (torquata body green with lateral and median lobes of the head and anterior margin of the pronotum yellow), less abundant than the former, was more frequent at latitudes > 23º18' S and mean annual temperatures < 20.8ºC (Southern Region). Type Y (aurantiaca – body entirely gold or orange), which is rare, was collected only in the Southern Region. N. viridula (smaragdula) was captured in only one place in the Northern Region (Boa Vista, RR, latitude 2º 49' N). The abundance of the two most common types, smaragdula and torquata, was not correlated with altitude.

Key words: Insecta, southern green stink bug, polymorphic type

RESUMO

Nezara viridula (L.) é um pentatomídeo cosmopolita e polimórfico. Vários tipos geneticamente determinados têm sido descritos devido à variação de coloração de adultos. Com o objetivo de mapear a distribuição geográfica dos tipos no Brasil, foram feitos levantamentos em 2001 e 2002 em 13 estados. Os percevejos do tipo G (smaragdula – totalmente verde) foram mais comuns e apresentaram distribuição ampla, ocorrendo de norte a sul do país (latitude 2º 49'N a 31º 46' S), exceto na Região Centro-Oeste. Os percevejos do tipo O (torquata - corpo verde com os lobos laterais e medianos da cabeça e margem anterior do pronoto de cor amarela), menos abundantes que o anterior, restringiram-se a locais com latitudes maiores que 23º18' S e temperaturas médias anuais < 20,8ºC (Região Sul). Percevejos do tipo Y (aurantiaca - totalmente amarelo ou alaranjado), de ocorrência esporádica, foram coletados somente na Região Sul. O tipo N. viridula (smaragdula) foi coletado em apenas um local na Região Norte (Boa Vista, RR, latitude 2º 49' N). Não se observou correlação da abundância dos tipos mais comuns smaragdula e torquata com a altitude.

Palavras-chave: Insecta, percevejo verde, tipo polimórfico

Nezara viridula (L.) is a cosmopolitan and polymorphic pentatomid. Of the nine polymorphic types of N. viridula described, the three main types are: type G = smaragdula Fabricius – body entirely green; type O = torquata Fabricius – body green with lateral and median lobes of the head and anterior margin of the pronotum yellow; and type Y = aurantiaca Costa – body entirely yellow or orange (Yukawa & Kiritani 1965).

In Brazil, of the nine polymorphic types of N. viridula, only the three more common types, G, O, and Y, are present, mostly in the Southern Region. However, two other types derived from the basic types G and O, having a yellowish-green background instead of green, were recently collected; the G-yellowish type was obtained from the field in Londrina, PR (latitude 23º18' S), and the O-yellowish type was obtained in the laboratory (Vivan & Panizzi 2002). It is known that different intermediate morphs of N. viridula originating from the basic types might be obtained in the laboratory by crossing (Ohno & Alam 1992), but this also occurs in the field.

N. viridula is more adapted to the cooler temperatures of southern Brazil (Panizzi & Corrêa-Ferreira 1997). However, recently it has expanded toward the warmer regions with lower latitudes, such as northeast Brazil (Panizzi 2002), probably following the expansion of its preferred host plant, soybean, Glycine max (L.) Merrill. Little is known about the biology and ecology of the genetically determined types of N. viridula, how they are distributed and how they are impacted by natural enemies and pesticides. Answers to these questions are important in order to design effective integrated management systems against the pest. Therefore, this study was conducted in order to learn the geographical distribution of the three main types of N. viridula, in the traditional and in the expanding regions of its occurrence.

Material and Methods

Localities of survey. During January-March 2001 and 2002, N. viridula adults were surveyed, each year, in 19 localities of 13 different states out of the 26 states of the country. The latitude and altitude of each place were recorded (Table 1).

Host plants examined. In general, bugs were collected from soybean plants. This is a preferred host, widely cultivated in Brazil. Plants examined were, in general, in the reproductive period, which is the time when bugs move from alternate hosts to feed on soybeans' fruiting structures (pods). Other host plants examined included cabbage, Brassica oleracea L. (Cruciferae), common bean, Phaseolus vulgaris L. (Leguminosae), pigeonpea, Cajanus cajan (L.) Millsp., and okra, Hibiscus esculentus L. (Malvaceae).

Insect sampling and storage. From each locality, 10 samples were taken at random, using either a sweep net or a beat cloth, depending on the type of plants available. Usually on soybean and greenbean, the beat cloth was used. The samples consisted of beating soybean plants over the beat cloth 20 times. On the other host plants the sweep net was used, sweeping the plants 20 times. Adults of N. viridula captured were killed, using killing jars, and were pinned and stored in the Insect Collection of Embrapa Soja, in Londrina, PR.

Statistics. The total number of adults of each type was recorded and the percentage of adults calculated for each place where the samples were taken. Data on the number of adults N. viridula of the main two types (smaragdula and torquata) obtained in each place were submitted to the analyses of regression, to examine the relationship between the number of insects captured and the latitude, the temperature (annual mean temperature of last 10 years), and the altitude. These analyses were performed using the program Statistical Analysis Systems (SAS 1997).

Results

Of the 13 states surveyed, in 19 localities, N. viridula was captured in eight states, in 14 localities, in particular in the southern states of Rio Grande do Sul, Santa Catarina, and Paraná, where all three basic types were collected (Fig. 1). N. viridula was not collected in the western states of Mato Grosso do Sul (Dourados - 22º 14' S), and Mato Grosso (Rondonópolis - 16º 29' S), the central state of Goiás (Santa Helena de Goiás - 17º 47' S), the northern state of Pará (Belém - 1º 32' S), and the north-western state of Acre (Rio Branco - 9º 58' S). Type G (smaragdula) was present in all 13 states, showing a greater distribution and adaptability to a wide range of environments. Types O (torquata) and Y (aurantiaca) were restricted to the three states of the South Region, around or below the Tropic of Capricorn (latitude 23º 30' S) (Fig. 1).

During 2001, 3,406 adults of N. viridula were collected, 100% of the specimens belonging to type G (smaragdula) in the northern locality of Boa Vista, RR (latitude 2º 49' N); in the northeastern localities of Barreiras, BA (12º 06' S), Petrolina, PE (9º 23' S), and Balsas, MA (7º 36' S); and in the southern localities of Assis, SP (22º 37' S) and Palotina, PR (24º 17' S) (Fig. 2 A). Over 95% of the bugs of type G were obtained in Londrina, PR (23º 18' S) and in Campo Mourão, PR (24º 02' S). In localities with latitudes > 27º S, in general, less than 90% of the bugs were of type G; the lower values were observed in Chapecó, SC (27º 07' S) (84.0%) (Fig. 2 A).

The second most abundant type (O - torquata) occurred in eight of the 14 localities where N. viridula was collected, restricted to the southern states of Paraná, Santa Catarina, and Rio Grande do Sul (Fig. 2 A). The values varied from 0.4% in Londrina, PR to 16.0% in Chapecó, SC, relatively high values (7.5 -12.5%) occurring in the localities of the southernmost state, Rio Grande do Sul. The rare type Y (aurantiaca) was collected only in Paraná state, in Londrina (0.7%) and Mariópolis (1.0%) (Fig. 2 A).

During the summer of 2002, results followed in general those from the previous year. No bugs were captured in Belém, Rio Branco, Dourados, Santa Helena de Goiás, and Rondonópolis, confirming the results obtained in 2001. In the remaining localities, the total of 2,828 specimens were collected, and 100% were of the type G (smaragdula) in all the same six localities as in 2001, plus Mariópolis and Ponta Grossa, both in Paraná state in the south (Fig. 2 B). In the other six remaining locations, the percentage of G types decreased to approximately 97% in Campo Mourão and Londrina, to 92% in Chapecó, and to approximately 89% in the three localities of Rio Grande do Sul state, Cruz Alta, Passo Fundo, and Pelotas (Fig. 2 B). In 2002, type Y (aurantiaca) was recorded in three locations in the South Region, namely Londrina (1.2%), Cruz Alta (07%), and Passo Fundo (0.2 %).

The regression analysis comparing the number (%) of N. viridula of the two main types, G (smaragdula) and O (torquata), with latitude indicated that as the latitude increased, the percentage of type G collected decreased, and the % of type O increased (Fig. 3). Although the data obtained in 2001 only show a tendency for this trend (for type G, F = 4.40; P = 0.0465; for type O, F = 4.26; F = 0.0498) (Fig. 3 A), in 2002, the data do yield a significant coefficient of determination (R²) with the approximate value of 0.7 (for type G, F = 8.08; P = 0.0098; for type O, F = 9.53; F = 0.0060) (Fig. 3 B), indicating that, in fact, the O type increases in abundance to the south and greater latitudes.

Regarding the relation between types G and O of N. viridula and temperature, the regression analyses indicated that as temperatures increased the number of the G types collected also increased (2001, F = 5.88; P = 0.0232; 2002, F = 45.20, P = 0.0001), in contrast to the O type, which was less abundant in areas with increasing temperatures (2001, F = 5.88; P = 0.0232; 2002, F = 63.65, P = 0.0001) (Fig. 4 A,B).

Considering the altitude (m), no relationship was found between this parameter and the number of bugs of types G (smaragdula) (2001, F = 0.07, P = 0.7912; 2002, F = 0.59, P = 0.4588) and O (torquata) (2001, F = 0.03, P = 0.8623; 2002, F = 0.67, P = 0.4334) (Fig. 5 A,^B). The coefficients of determination (R²) values were very low and not significant in either year. The suspicion that with an increase in altitude, temperatures will be lower and will favor type O, and, in consequence, decrease the percentage of individuals of type G, was not confirmed.

Discussion

These extensive surveys indicate that the southern green stink bug, N. viridula, is broadly distributed in Brazil, and that type G (smaragdula) is the most widespread, covering a wide range of latitudes from 31º 46' to 2º 49' S. This type is believed to have greater ability to adapt to different environments than the others (Kiritani 1970). Despite this ability, it seems that N. viridula is unable to thrive in the areas of the Central-West Brazil, where it was not intercepted, confirming data from former studies that have not reported its presence in this region in the past (Corrêa et al. 1977), and more recently (Borges 1992). This could be due to several factors such as the impact of high temperatures during most of the year, a greater impact of natural enemies such as tachinid flies (Corrêa-Ferreira 1984) and egg parasitoids (Corrêa-Ferreira & Moscardi 1995) active year round, and stronger competition with other pentatomids, such as Euchistus heros (Fabricius) and Piezodorus guildinii (Westwood), which are prevalent in this area on soybean plantations (Panizzi 1997). At this point, however, there is no clear explanation of why N. viridula does not occur or is rare in the Central-West.

The wide range of distribution of N. viridula confirms recent studies that report its increasing expansion towards Northeast Brazil (Panizzi 2002). It seems that this pentatomid is spreading in other areas of the world too, such as northward in Japan, due to climate warming (Musolin & Numata 2003).

The fact that type O (torquata) is present only in the South Region, and, within this area, is more abundant toward southern locations of higher latitudes, indicates that this type is better adapted to cooler temperatures. Data on nymph biology and adult reproduction of type O in the laboratory, comparing different temperatures, demonstrate its better adaptability to lower temperatures than the most common type G (Vivan & Panizzi 2005).

The proportions among the types found in Brazil, the type G being much more abundant than the others, and type Y being rare, are in accordance with data in the literature for other regions of the world. For example, in a survey conducted in Macau (China), 85% of the specimens were of type G, 13% of type O, and less than 0.2% of type Y (Easton & Pun 1997). Hokkanen (1986) reported one specimen of type Y of 203 individuals (0.5%) in the United States. Because this last type was rare, no relationship of its occurrence with the latitude or temperature can be done.

The capture of N. viridula in the North Region in Boa Vista, RR (latitude 02º49' N) is a new record of its distribution in Brazil, and it means that the bugs are present at least in some localities of this area where soybean is being introduced, since they were not captured in Belém, PA (latitude 1º 32' S) nor in Rio Branco, AC (latitude 9º 58' S) toward the west, where the crop is absent. Very probably N. viridula is already present in these two last states, feeding on wild legumes, but no records of its presence are available.

The significant positive correlation of latitude and negative correlation of temperature with the occurrence of type O (torquata) demonstrates that this type is more adapted to areas with lower mean temperatures, and during the summer with longer days and during the winter shorter days.

In conclusion, the data from these surveys indicate that N. viridula is widespread in Brazil and that type G (smaragdula) is the best adapted to colonize different environments. Type O (torquata) is favored by the conditions in the South Region, which allow the gene(s) responsible for the polymorphism to be expressed.

Acknowledgments

We thank the following persons who helped in collecting the insects and provided facilities to process the samples: Jovenil J. Silva, Luiz A.B. Salles, José R. Salvadori, Mauro T. B. Silva, Luis A. Chiaradia, Marcilio J. Thomazini, and Francisca N. P. Haji. Lúcia Vivan was supported by a scholarship from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and by the laboratory and field facilities provided by the Centro Nacional de Pesquisa de Soja of Embrapa, Brazil. We also thank Carl W. Schaefer and Lenita J. Oliveira for checking the manuscript.

Received 20/X/04. Accepted 10/X/05.

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Publication Dates

• Publication in this collection
  10 July 2006
• Date of issue
  Apr 2006

History

• Accepted
  10 Oct 2005
• Received
  20 Oct 2004