Liliana Rojas ¹ , Carolina Godoy ² , Paul Hanson ³ and Luko Hilje ⁴ *

* Address for correspondence: Fax (506) 556-0606, e-mail: lhilje@catie.ac.cr

Received 06-VI-2000. Corrected 01-II-2001. Accepted 08-II-2001.

Key words: Coffee, poró, laurel, shade trees, biodiversity, Homoptera, Costa Rica.

The study, conservation, and utilization of tropical biodiversity are current major issues among conservation biologists (Wilson 1988). Nevertheless, research has been focused mainly on pristine ecosystems, to a large extent disregarding the actual or potential value of biodiversity in agroecosystems (Vandermeer and Perfecto 1997). For instance, agroecosystems such as shaded coffee plantations in Mesoamerica are an important refuge for biodiversity, including birds and insects (Perfecto et al. 1996). Some Hymenoptera and Coleoptera groups have high levels of diversity in traditional coffee plantations (Nestel et al. 1993, Perfecto and Vandermeer 1994, Perfecto and Snelling 1995, Perfecto et al. 1997), which resemble natural forests in terms of their multistrata structure and floristic diversity (Perfecto et al. 1996).

Shade trees in these systems play important agronomic and economic roles (Beer et al. 1998). Combinations including nitrogen-fixing trees, such as poró (Erythrina poeppigiana (Walpers) O.F. Cook, Fabaceae: Papilionoideae) and laurel (Cordia alliodora (Ruiz and Pavón) Oken, Boraginaceae), are rather common in several areas of Costa Rica. From either a species conservation or a pest management standpoint, it is important to know whether these systems, with only one or two tree species, can harbor and maintain a high diversity of insect species, in comparison to coffee monocultures.

This paper reports on the particular homopteran groups present in these systems, whereas data on patterns of species diversity and similarity appear elsewhere (Rojas et al. 2000).

The survey was carried out in Turrialba, Costa Rica, where average annual values of climatic variables are 2 616 mm precipitation, 21.7 ºC temperature, and 87.9 % RH. Even though Turrialba is located in the Caribbean watershed, where seasonality is not well defined (Herrera 1985), the eight-month sampling period (March-October, 1997) allowed collecting of a representative sample of homopteran species during both dry and rainy periods.

Sampled coffee farms were located between 600-800 m elevations, at 9º 55’ N and 83º 39’ O, within premontane wet forest and tropical moist forest life zones. Presence and abundance of homopteran species were recorded in three systems: unshaded coffee (C), coffee-poró (CP), and coffee-poró-laurel (CPL). Three commercial farms were sampled for each system on three dates. Farms differed in coffee variety, planting densities, and size, as well as in the type of surrounding vegetation.

Four hundred coffee plants and 20 poró or laurel trees were sampled in each farm. Poró and laurel trees were selected so that they did not exceed 3 m in height, to allow sampling with an aerial insect net. Each coffee plant was swept three times with the net, at different heights, whereas the poró and laurel trees were swept 15 times along the lower edge of their crown. Samples were placed in plastic bags and taken to the laboratory, where they were killed. Specimens were separated to morphospecies and the numbers of individuals per species were recorded. Representative specimens were mounted and identified by one of the authors (C. Godoy).

A total of 10 612 specimens, representing 130 species in ten families, were collected during the study. The number of species follows: Cicadellidae (82), Membracidae (22), Cercopidae (6), Flatidae (4), Delphacidae (3), Derbidae (3), Dictyopharidae (3), Issidae (3), Tropiduchidae (3), and Cixiidae (2) (Table 1). Eight families in common were represented among the three systems. Delphacidae and Dictyopharidae were not found in unshaded coffee. Species richness was highest in the coffee- poró (CP) (88), followed by the coffee-poró-laurel (CPL) (74) and the unshaded coffee (C) (60) (Table 1).

Table 1

Cicadellidae represented 58 % of the species and 71 % of the individuals, followed by Membracidae and Cercopidae. At least four species of Cicadellidae (Omegalebra n. sp., Oncometopia n. sp., Nielsonia n. p. and Cicadellidae n. sp.) are undescribed. Not all species were equally abundant (Table 2). In the unshaded coffee system, 13 % of the species were represented by 100-1 000 individuals, 19 % by 10-100 individuals, and 68 % by less than 10 individuals. In the coffee-poró system, a single species (1 %) had more than 1 000 individuals, 10 % had between 100-1 000, 25 % had between 10-100, and 63 % had less than 10 individuals. In the coffee-poró-laurel system, one species (1 %) had more than 1 000 individuals, 8 % had between 100-1 000, 29 % had between 10-100, and 62 % had less than 10 individuals.

Table 2

Table 3

Species similarity was highest between the CP and CPL systems, which shared 55 (51 %) of the 107 species present; C and CP systems shared 41 (39 %) out of 104 species, and the C and CPL systems shared 37 (38 %) out of 97 species. Most shared homopteran species between systems were barely represented in any of the compared systems. Fusigonalia lativittata, Neocoelidia sp. and Scaphytopius ca. latidens were consistently high in the three systems, although their densities were always higher in coffee shrubs. Empoasca sp., Bothriocera sp. and Derbidae sp. 1, which were almost absent from the C system, were the most abundant shared species between the CP and CPL systems. They always reached higher numbers in poró trees.

Discussion

The fact that not all homopteran species were equally abundant in each of the three systems studied reveals that they follow the same pattern observed in natural communities (Krebs 1978). In this case, the dominant (i.e. most abundant) species for the coffee-tree communities were F. lativittata, H. nicaraguensis, Neocoelidia sp., Oliarus sp. and Clastoptera sp.

In addition, data suggest that diversification of the coffee agroecosystem directly or indirectly favors some species while limiting others, but had no effect on the majority of species. For instance, Graphocephala sp. 1 was the dominant species in unshaded coffee, but its numbers declined drastically when coffee was associated with either poró or laurel. The species was barely present in poró but not in laurel, and its numbers in coffee declined severely as diversification increased, to the point that in the CPL system it did not appear in coffee. Other congener species, Graphocephala sp. 3 and Graphocephala sp. 2, showed an analogous trend. It is possible that microclimatic changes associated with diversification could have given rise to these patterns for homopteran species closely associated with coffee, as coffee itself did not vary within any of the three systems, except for normal variations in variety and age, as well as in planting densities. In contrast, F. lativittata, which also has a close association with coffee, reached highest numbers in the CP system, fewer in the C system, and dropped sharply in the CPL system.

Other homopteran species seem to benefit from diversification, at least to some extent. For instance, there was a great deal of variation for other species closely associated with coffee which also appeared in poró and laurel. Even though all of them preferred coffee regardless of the system, their highest numbers were attained in different systems. Thus, Neocoelidia sp. and Clastoptera sp. reached highest numbers in the CP system, whereas S. ca. latidens did so in the CPL system. Colpoptera sp. showed rather even numbers between the C and CP systems and was more common in laurel than in coffee in the CPL system. Finally, Oliarus sp. was almost absent in coffee in the CPL system. It is likely that varying responses of homopteran species to diversification are more complex, perhaps involving a combination of factors related to both coffee systems (variety, age, planting densities, amount of shade, size, and surrounding vegetation) as well as to hopper differential ability to exploit food resources associated with foliage of coffee, poró and laurel trees.

Four species (H. nicaraguensis, H. panamensis, Omegalebra n. sp. and Micrutalis sp.) were abundant and appeared almost exclusively on laurel trees. This peculiarity in species composition may be explained not only in terms of specific preferences for laurel foliage, but also because of tree isolation, as laurel trees are sparsely planted in coffee plantations. In Turrialba, a hectare of coffee typically contains 70-150 laurel trees, 155 poró trees and 5 000-6 000 coffee shrubs. Moreover, isolation of laurel trees is increased by lack of disturbance throughout the year, as the lower branches are the only ones occasionally pruned.

In regards to species similarity, it was highest between the CP and CPL systems. Nonetheless, Rojas et al. (2000) showed that species diversity was higher in the CP system (2.84), than in the most complex system (CPL) probably owing to the latter generally receives less external inputs, such as fertilizers. Also, Rojas et al. (2000) provide a more detailed analysis of similarity patterns within each system, considering plant components (coffee, poró or laurel), geographic location of each plot and sampling date.

In summary, from a species conservation viewpoint, these results reinforce the idea that even disturbed systems can harbor many insect species, including some undescribed ones, so that they deserve to be studied in terms of their biodiversity patterns (Vandermeer and Perfecto 1997). On the other hand, from a pest management standpoint, even though homopterans have not been reported as coffee pests in Costa Rica (Anonymous 1989), shade trees may play a role in maintaining populations of their parasitoids and predators, thus possibly preventing homopteran outbreaks. However, this requires more study.

Acknowledgments

To Fundatrópicos and ODA (Overseas Development Administration), which made it possible for the first author to carry out her graduate studies. To Guillermo Ramírez (ICAFE) and the coffee farmers (La Isabel, Pavones and Verbena farms) for their logistical support. Finally, to Paul Freytag (University of Kentucky), for help in the identification of Typhlocybinae.

Resumen

En Turrialba, Costa Rica, se efectuó un inventario de especies de chicharritas (Homoptera: Auchenorryncha) en plantaciones de café sin sombra (C), así como en café asociado con árboles de poró (Erythrina poeppigiana) (CP) o de poró y laurel (Cordia alliodora) (CPL). Se recolectaron 131 especies, pertenecientes a diez familias, entre las cuales predominó Cicadellidae (82 especies). La riqueza de especies fue mayor para el sistema CP (88 especies), seguido por CPL y C, con 74 y 60 especies, respectivamente. Las cinco especies más comunes para los tres sistemas juntos fueron Fusigonalia lativittata, Hebralebra nicaraguensis, Neocoelidia sp., Oliarus sp. y Clastoptera sp. La diversificación del agroecosistema cafetalero parece favorecer a algunas especies y limitar a otras, pero no influye en la mayoría de ellas. Así, solamente F. lativittata, Neocoelidia sp. y Scaphytopius ca. latidens estuvieron bien representadas en los tres sistemas, aunque fueron más abundantes en los arbustos de café. Asimismo, las siguientes especies particulares fueron dominantes para cada sistema: Graphocephala sp. 1 (C), F. lativittata (CP) y H. nicaraguensis (CPL). Cuatro especies que fueron abundantes en los árboles de laurel, incluyendo a H. nicaraguensis, aparecieron casi exclusivamente en estos árboles. La similitud de especies fue mayor entre los sistemas CP y CPL (51 % de las especies en común), mientras que fue de 39 % entre C y CP, y de 38 % entre C y CPL. Estos hallazgos muestran que incluso algunos sistemas perturbados pueden albergar muchas especies de insectos, por lo que merecen la atención de los biólogos y conservacionistas.

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