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versión On-line ISSN 0718-1620
Cienc. Inv. Agr. vol.38 no.3 Santiago dic. 2011
Cien. Inv. Agr. 38(3):367-377. 2011
Diversity and distribution of the Aegorhinus genus in the La Araucanía Region of Chile, with special reference to A. superciliosus and A. nodipennis
El género Aegorhinus, diversidad y distribución en la Región de La Araucanía, Chile, con especial referencia a A. superciliosus y A. nodipennis
Andrea Zavala1, Mario Elgueta2, Juan Abarzúa1, Alfonso Aguilera1, Andrés Quiroz3, and Ramón Rebolledo1
1Facultad de Ciencias Agropecuarias y Forestales. Universidad de La Frontera. Casilla 54-D. Temuco, Chile.
2Museo Nacional de Historia Natural. Santiago, Chile. Casilla 787, Santiago, Chile.
3Facultad de Ingeniería, Ciencias y Administración. Universidad de La Frontera. Casilla 54-D. Temuco, Chile.
The Araucanía region is a berry producing area where important behavioral aspects of species in the genus Aegorhinus, a pest that affects crops, are still unknown. The objectives of this study were to determine the distribution, abundance and richness of these species in agroecological zones of La Araucanía Region and to determine the hosts in which they were found. The sites where these species were found were represented on a map divided into grids of 25 x 25 km. Eight species of Aegorhinus were found in the area, and Aegorhinus nodipennis and Aegorhinus superciliosus were the most abundant. The diversity was analyzed using the Shannon-Wiener index, and the equitability was determined using the Pielou index. The agroecological zone with the greatest diversity of the region corresponded to mountain ranges; however, the central plain registered the highest abundance of individuals. This study introduces new hosts for six of the eight species found in the region.
Key words: Aegorhinus, agroecological zones, Coleoptera, hosts.
En la región de La Araucanía, área productora de berries, aún se desconocen aspectos relevantes del comportamiento de los integrantes del género Aegorhinus, considerados plagas importantes en estos cultivos, por lo que este estudio tuvo como objetivos determinar la distribución, riqueza y abundancia de estas especies en las zonas agroecológicas de La Araucanía y sus hospederos. Los puntos donde se encontraron estas especies fueron representados en un mapa dividido en cuadrículas de 25 km x 25 km. Se registraron ocho especies de Aegorhinus, siendo Aegorhinus superciliosus y Aegorhinus nodipennis las especies más abundantes. La diversidad se analizó a través del índice de Shannon-Wiener; y la equiparabilidad con el índice de Pielou. La zona agroecológica con mayor diversidad para la región correspondió a la cordillera, sin embargo en el llano central se registró la mayor abundancia de individuos. En este trabajo se dan a conocer nuevos hospederos para seis de las ocho especies encontradas en la región.
Palabras clave: Aegorhinus, Coleoptera, hospederos, zonas agroecológicas.
Aegorhinus Erichson and Alastoropolus Kuschel are the only genera of the Aterpini tribe (Coleoptera: Curculionidae) in South America (Elgueta and Marvaldi, 2006). In Chile, they are located from the central to the southernmost zones, i.e., from 32° 02' to 53° 08' south latitude.
Similarly, they can be found in the Andean forests of southern Argentina (Morrone and Roig-Juñent, 1999). Within this tribe, the Aegorhinus genus is the most diverse and contains 24 species (Kuschel, 1951; Cekalovic, 1970; Elgueta, 2000). Moreover, A. superciliosus, A. nodipennis and A. phaleratus constitute major agricultural pests in Chile. A. superciliosus is considered the most important species in La Araucanía region due to its negative impact on the production of berries (Aguilera, 1988, 1990). Most species are associated with deciduous forests and Valdivian temperate forests from the Maule to Los Lagos Regions (Klein and Waterhouse, 2000; Marvaldi and Elgueta, 2006). Approximately 30% of Aegorhinus spp. are closely linked to species formations of Fagaceae (Elgueta, 1974). Of all the Aegorhinus species, only three are considered major agricultural pests in Chile, namely, A. phaleratus and A. superciliosus associated with berries (Gonzalez, 1989; Prado, 1991; Artigas, 1994; Klein and Waterhouse, 2000; Cisternas, 2002; Aguilera, 2005) and A. nodipennis found mainly in Corylus avellana (European hazelnut). In addition, A. albolineatus has been described as an occasional raspberry pest in Rubus idaeus (Cisternas et al., 2000).
The larvae and adult stages of A. phaleratus and A. superciliosus, which are reported as being responsible for the damage to their host species, are similar in shape and color; however, they have distinctive characteristics and different geographical distributions (Elgueta, 1993). The first is found from Valparaiso to the Maule Region, whereas the second is established between the Maule and Los Lagos Region. Moreover, both species have a wide host range (Prado, 1991; Elgueta and Marvaldi, 2006 and Parra et al., 2009a).
A. nodipennis is considered one of the most important hypogea insects that affect growing European hazelnut plants due to its frequent presence in farms and its life habits during the larvae stage (Aguilera, 2005). A. superciliosus is found in several fruit tree species (Kuschel, 1951; Parra et al, 2009a) and, together with A. nodipennis, is considered one of the most common pests in Valdivian forests (Artigas, 1994). Interestingly, there is plenty of literature regarding their host species (Kuschel, 1951; Prado, 1991; Artigas, 1994, Klein and Waterhouse, 2000; Cisternas, 2002; Aguilera, 2005; Elgueta and Marvaldi, 2006; Parra et al, 2009a).
Research on Aegorhinus in Chile is mostly focused on its geographic distribution (Aguilera, 1988, 1995; Elgueta, 1993; Artigas, 1994; Arias, 2000), morphological description (Kuschel, 1951; Aguilera, 1988; Aguilera and Rebolledo, 2001; Carrillo et al, 2002) and on damage and control (Kuschel, 1951; Aguilera, 1988, 1995; Prado, 1991; Carrillo, 1993; Elgueta, 1993; Cisternas et al, 2000; France et al, 2000; Parra et al, 2009b; Mutis et al, 2009).
In the La Araucanía Region, the diversity and distribution of species infecting cultivated and wild hosts is unknown; moreover, there is no information regarding possible preferences for certain host species. Therefore, this study aimed at determining the distribution, richness and abundance of Aegorhinus species in different agroecological areas of La Araucanía. Similarly, we identified the hosts where these insect species could be found.
Materials and methods
Sampling was performed at different sites in each agroecological zone of the La Araucanía region (37° 35' and 39° 37' south latitude) as described by Rouanet et al. (1988). At each site, we identified the Aegorhinus species and plants on which the insects were found. A regional map including the agroecological zones and a grid of 25 x 25 km was used for sampling (Figure 1). Each grid was designated by a pair of letters, which were never repeated within the same area. At least 20 sampling points per agroecological zone were randomly chosen, resulting in a total of 122 points for the region. La Araucanía is located in the UTM (Universal Transversal Mercator) zones 18 (central meridian of longitude -75°) and 19 (central meridian of longitude -69°; Borgel, 1983).
|Figure 1. Map of agroecological zones with grids of 25 x 25 km in La Araucanía region. (Methodology adapted from Pascual and Montserrat, 1988).|
The insect sampling was conducted between September 2008 and April 2009 using three methods: a) shaking the foliage on an entomological umbrella, b) scanning of entomological nets on herbs, shrubs and wild or cultivated trees according to the environmental situation of each sampling station and c) visual observation. Each collected individual was recorded with a numerical identifier (ID), collection location, geographical location, altitude and host in which it was found.
Abundance and infestation
The abundance of insects per plant was estimated according to the following scale:
Low = one to three individuals
Median = four to six
Abundant = seven to ten
Very abundant = more than ten individuals
The percentage of Aegorhinus infestation per plant was determined by the following equation:
Distribution map and population indices
To prepare the distribution maps of the Aegorhinus species, coordinates were obtained at each sampling site using a global positioning system and the GPS III Plus software (GARMIN International, Kansas, USA, 2008). The maps were elaborated from the GPS database in the laboratory of Ordenación y Planificación Territorial of the Facultad de Ciencias Agropecuarias y Forestales of the Universidad de la Frontera using the ArcGIS 9 software program, version 9.2 ArcMap (ESRI USA, 2004). With the obtained data, several population variables such as richness (S), total abundance of individuals (N), relative abundance (AB%) and alpha diversity were calculated for each agroecological area using the Shannon-Wiener (H'), Pielou equity index (J) and maximum diversity (H' max) indices (Moreno, 2001).
Results and discussion
Eight Aegorhinus species were identified in the region: A. superciliosus (Guérin), A. nodipennis (Hope), A. schoenherri (Gay & Solier), A. suturalis (Blanchard), A. ochreolus Kuschel, A. oculatus Kuschel, A. silvícola Kuschel and A. bulbifer Kuschel. Of the eight species, three were found in the coastal rain-fed area, three in the interior rain-fed zone, five in the central plain, four in the Andes foothills and six in the Andes mountains. Of all the species, A. superciliosus and A. nodipennis were collected in the five assessed agroecological areas (Table 1).
Distribution and abundance
A total of 11,770 Aegorhinus spp. individuals were counted, and the central plains and the Andean foothills had the highest number of individuals, 6,629 and 4,793, respectively. Most of the specimens were collected from blueberries (Vaccinium corymbosum) and raspberries (R. idaeus) plants. The lowest abundance was found in the Andes mountains, with 69 individuals (Figure 2).
|Figure 2. Total number of specimens of the genus Aegorhinus registered in the agroecological zones of La Araucanía region, Chile. Foothills and range correspond the Andes mountain range (see Figure 1).|
Of all the species found in this study, the two most abundant in the Araucanía region were A. superciliosus (9,963 individuals) and A. nodipennis (1,692 individuals), which corresponded to 99.02% of the total registered (Table 1). The abundance of these two species might be explained by their host preference, berry plants, as suggested by several authors (Aguilera, 1988, 1990 and 1995; Parra et al, 2009b). In addition, A. ochreolus, A. schoenherri, A. suturalis and A. silvicola were considered fairly abundant species, where as the remaining species were considered median.
Regarding the geographic distribution of each species, A. superciliosus dominated in four agro-ecological zones: the Andes foothills (87.57%), the coastal rain-fed zone (85.86%) and the central plains (83.77%), where the highest relative abundances were found. The second most abundant species was A. nodipennis, with a higher total abundance in the central plains and in the Andean foothills; however, its higher relative abundance, i.e., the percentage of total individuals, occurred in the mountains and in the interior rain-fed zone. The third most abundant species was A. schoenherri, with the highest abundance and relative abundance in the Andes foothills (Table 1).
Interestingly, most Aegorhinus species found in La Araucanía had low population levels and did not become pests in orchards or other crops of economic importance in the region. In contrast, the most abundant species were A. superciliosus and A. nodipennis, which are considered pests with a wide host range and great economic impact on fruit trees in Chile. The presence of these species might be a limiting factor for growing fruit trees in the area.
The area with the lowest species diversity, according to the Shannon-Wiener index, corresponded to the Andes foothills (H' = 0.3822), followed by the coastal rain-fed zone (H'= 0.4298), central plains (H'= 0.4775), interior rain-fed zone (H'= 1.0103) and the Andes mountains (H'= 1.2109; Table 2). Although the abundance of individuals was higher in these last two areas, their distribution was not even because, in both sectors, A. superciliosus represented over 80% of the individuals collected.
Less diverse areas could be the result of environmental degradation due to anthropogenic factors such as the introduction of exotic plant species, location of urban zones and land use for livestock and agriculture (Vergara et al., 2006). Similarly, the diversity and distribution of other Coleoptera species in the area might reflect the impact of these factors. For example, the most abundant plant species in the coastal rain-fed zone are Pinus radiata and Eucalyptus globulus. In the central plain, blueberries (V. corymbosum) were introduced as an exotic monoculture.
These results are consistent with previous studies (CONAMA, 2002) in which the greater distance among native forest species (with the coastal rain-fed area presenting the greatest distance), the greater intervention they have suffered, so that the natural conditions for establishment and natural flows between species, i.e., biodiversity, considerably declines. However, our results differ from those of Vidaurre et al. (2008), who in a study with dung beetles in Bolivia, described decreased levels of abundance and richness in forests better preserved versus in disturbed habitats. Therefore, disturbed areas supported relatively less abundance and richness than native forests, demonstrating the close relationship that exists with conservation. While this result was coincident with regard to species richness, the abundance differed because the interior rain-fed area and the Andes mountains were the sectors with the lowest levels of exotic plant introduction (CONAMA, 2002) and presented the lowest abundances of Aegorhinus individuals. The persistence of species in natural environments largely depends on the intensity and frequency of spatial disturbances of natural and man-made habitats on the land (Escobar and Chacón de Ulloa, 2000).
According to our results, the lowest Aegorhinus diversity occurred in the Andean foothills, and the most diverse sector was the Andean mountains, which, together with the central plain, had the highest species richness. The scarcity of some Aegorhinus species might be the result of the sampling dates because they might have been directly linked to certain stages in the phenology of their hosts. Others, however, appeared to be associated with certain environments, such as A. ochreolus, which was found in dense forests of Drymis winteri in the central plain, whereas A. schoenherri and A. silvicola were exclusively related to the Andes mountains.
Altitude and hosts
With respect to altitude, the most abundant Aegorhinus species ranged from 10 to 1,350 m in altitude (Figure 3).
|Figure 3. Altitudinal range in which the most abundant Aegorhinus species were found in La Araucanía region, Chile.|
The greatest but least diverse abundance, registered in the central plain, was associated with the most abundant species (A. superciliosus and A. nodipennis), which colonized a greater number of hosts distributed in lower elevation locations (Kuschel, 1951; Prado, 1991; Artigas, 1994; Klein and Waterhouse, 2000; Cisternas, 2002; Aguilera, 2005; Elgueta and Marvaldi, 2006).
In the highest areas of the region, except for the mountains, plant diversity was lower because exotic forest species (e.g., pine and eucalyptus) have been uniformly planted (CONAMA, 2002). In the Andes mountain range, the predominant vegetation corresponded to forests of Nothofagus, Araucaria araucana and Rhamnaceae species, such as Discaria serratifolia, which presented Aegorhinus species closely associated to only one host; similarly, A. schoenherri was found in D. serratifolia and Maytenus boaria (Table 3).
There were eight new hosts for A. superciliosus, but its presence on Acacia dealbata was probably accidental. A. nodipennis was observed on five new hosts, and it was abundant in M. boaria, Betula pendula and Salix viminalis. A. suturalis was first found in Lomatia hirsuta and R. idaeus, which constituted unknown hosts for this species.
A. schoenherri was associated with hosts of the Rhamnaceae family. These results are coincident with those of Arias (2000), who mentioned Discaria serratifolia (chacay) as host plant, but it was also found inM. boaria, which would be a new host for this species.
Regarding host preference, we found the highest presence of Aegorhinus in the following species: M. boaria (79%), Rosa moschata (54.2%), D. winteri (46.3%), Rubus ulmifolius (44.4%) and L. hirsuta (44.1%; Table 4). Despite being one of the species with the greatest Aegorhinus presence in the city of Temuco, B. pendula only reached 15.8% at the regional level. Consistent with our results, Parra et al. (2009a) reported M. boaria, D. winteri and R. ulmifolius, among others, as hosts of A. superciliosus. V. corymbosum and R. idaeus were excluded from the analysis because the insects counted in these host species corresponded to sporadic catches made by farm workers (Table 4).
Aegorhinus specimens were not found in A. araucana, Citrus sinensis, Crinodendron patagua, Cryptocaria alba, Cupressus macrocarpa, Eri-obotrya japonica, Eucryphia cordifolia, Luma apiculata, Malus sp., Persea lingue, Prunus cerasus and Prunus domestica. However, there are reports on Cryptocaria alba as a host of A. phaleratus; Eucryphia cordifolia as a host of A. nodipennis; Malus domestica as a host of A. nodipennis, A. phaleratus and A. superciliosus; Prunus cerasus as a host of A. phaleratus and A. superciliosus; and P. domestica as a host of A. nodipennis, A. phaleratus and A. superciliosus (Kuschel, 1951; Prado, 1991; Artigas, 1994; Arias, 2000; Klein and Waterhouse, 2000; Cisternas, 2002; Aguilera, 2005; Elgueta and Marvaldi, 2006).
The distribution of species considered most important as agricultural pests, A. superciliosus and A. nodipennis (Figure 4), and the least abundant or of less agricultural importance (Figure 5) were represented separately in maps of the La Araucanía region. The agroecological zones were illustrated in both maps.
|Figure 4. Distribution of Aegorhinus superciliosus and A. nodipennis in different ecosystems of the La Araucanía region, Chile.|
|Figure 5. Map of Aegorhinus species distribution with less agricultural importance in La Araucanía region, Chile.|
Regarding the ecosystem associated with these species, A. bulbifer was found in areas of arborescent matorral and open native forest. A. suturalis was found in open areas of open arborescent matorral and open prairie matorral. A. silvicola and A. schoenherri were associated with semi-dense adult native forest and open prairie matorral. A. oculatus was associated with semi-dense regrowth areas and open matorral. A. ochreolus was described in areas of perennial prairie with open native forests. A. superciliosus and A. nodipennis were distributed in areas strongly dominated by arborescent matorral.
According to our results, the species of Aegorhinus in the Araucanía region were A. bulbifer, A. nodi-pennis, A. ochreolus, A. oculatus, A. schoenherri, A. silvicola, A. superciliosus and A. suturalis. Six of these species, A. superciliosus, A. nodipennis, A. suturalis, A. silvicola, A. oculatus and A. schoenherri presented new hosts in La Araucanía region. Thus, the most novel findings of this study were the following: 1) A. superciliosus was found on A. dealbata, N. obliqua, N. pumilio, Populus alba, Betulapendula, Cynara scolymus, Discaria serratifolia and Lomatia hirsuta; 2) A. nodipennis was found on M. boaria, Salix viminalis, Betula pendula, Peumus boldus and Lomatia hirsuta; 3) A. suturalis was found on Lomatia hirsuta, R. idaeus and Salix viminalis; 4) A. silvicola was found on N. antartica; 5) A. oculatus was found on Discaria serratifolia and 6) A. schoenherri was found M. boaria.
The authors would like to acknowledge the financial support provided by Project DIUFRO DI10-101 from the University of La Frontera and project FONDECYT 1070270.
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Received February 24, 2010. Accepted June 9, 2011.
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