O. Alonso¹, J. C. Lezcano¹ y Moraima Suris²
1Estación Experimental de Pastos y Forrajes "Indio Hatuey"
Central España Republicana, CP 44280, Matanzas, Cuba
E-mail: osmel.alonso@indio.atenas.inf.cu
2Centro Nacional de Sanidad Agropecuaria, Mayabeque, Cuba

 

 

 

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ABSTRACT

In order to define the main functional groups in the insect community present in two areas consisting in the association of Leucaena leucocephala cv. Peru and Panicum maximum cv. Likoni (a silvopastoral system and a seed field, respectively), both located at the Experimental Station of Pastures and Forages "Indio Hatuey", the leaves, inflorescences and pods of the legume and the foliage from the grass were sampled every 15 days, for three years, to collect the insects. The classification of the groups was made from: the identification of each insect species, the information provided by literature about its main feeding habit and the field observations. With these elements the phytophagous and beneficial insects were defined, and as subgroups of the latter: predators, parasitoids, pollinators, organic matter decomposers, coprophagous and mycophagous insects. A total of 113 insect species were identified, 63 with phytophagous habits and the other 50 were beneficial. In the tree stratum 88 species were found, 49 phytophagous (56%) and 39 beneficial (44%); and there were 103 species in the herbaceous stratum, 59 phytophagous insects (57%) and 44 beneficial (43%); 78 species coincided in the two strata. It is outstanding that in both strata predators and parasitoids from the orders Hymenoptera, Coleoptera and Diptera prevailed, such as: Cycloneda sanguinea limbifer Casey, Coccinella maculata (De Geer), Chilocorus cacti Linnaeus, Conura sp., Pimpla marginella (Brullé) and Rogas sp. The structure and function of the insect community were concluded to show a relatively higher number of phytophagous insects as compared to the beneficial ones; however, the predominance of natural enemies, responsible for the regulating activity of phytophagous populations, which they keep below the economic damage threshold in the leucaena crops in the country, was important.

Key words: Insecta, Leucaena leucocephala, Panicum maximum.

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INTRODUCTION

In order to maintain or favor the biodiversity increase, in natural areas as well as agroecosystems, it is necessary to know about the structure and function of the communities of organisms which inhabit them (Bossart and Carlton, 2002). For such reason, it is essential to characterize the interactions among the components of the community or biocenosis, because it essentially refers to the trophic relations established among species (Schowalter, 1996).

Thus, the analysis of the communities regarding the functional groups present is mainly a valuable instrument because it is based on the similarity of functions of different species in a community, even though they do not occupy the same habitat. That is why the location of the insects in functional groups is supported primarily on the feeding way of each organism and the feed type they consume. The more frequently identified ones, due to their usefulness or because their identification is relatively easy are: herbivores, pollinators, predators, parasitoids, and decomposers (Cagnolo et al., 2002).

Considering all these aspects, and as in the field of agroforestry entomological studies are still little known, because there is not enough information in the tropics about the insects of higher presence in agroforestry systems (Singh, 2005) and in livestock production in general, the purpose of this work was to determine the main functional groups in the insect community present in two Leucaena leucocephala-Panicum maximum agroecosystems, which are in correspondence with the most extended in the country.

 

MATERIALS AND METHODS

Experimental procedure. Every 15 days, for three years, the leaves, inflorescences and pods of L. leucocephala cv. Peru and the foliage of P. maximum cv. Likoni, which were part of two livestock production agroecosystems, one for fattening growing cattle, corresponding to a silvopastoral system (13 ha, with a density of 396 trees ha-1 and six years of exploitation) and the other belonging to a seed field (0,2 ha, 3 000 trees ha-1 and 16 years of exploitation), were sampled; they were both located at the Experimental Station of Pastures and Forages "Indio Hatuey", Matanzas province and established on a lixiviated Ferralitic Red soil, according to the classification made by Hernández et al. (2003).

The objective of the samplings was the capture of insects by the following collection methods: transparent nylon bags, in 5% of the trees, and the entomological net in five spots, through 100 sweeps of it in the legume as well as the grass, which is equivalent to 25 m2, according to Faz (1990).

Definition of functional groups of the insect community. After the identification of each insect species, its function was determined according to the literature information about the main feeding habit and the observations made in the field; in addition, the criterion by Ruiz and Castro (2005) was taken into consideration, who defined as functional group "the set of species which have a similar ecological function, independently from the existing taxonomic relation among them", which coincides with classification made by Root (1967) and Cummins (1973). In this sense phytophagous and beneficial insects were considered functional groups, and the latter included as subgroups: predators, parasitoids, pollinators, organic matter decomposers, coprophagous and mycophagous insects.

After classifying each insect in the group to which it belongs, the percentage such group represented with regards to the total captured insects was calculated.

 

RESULTS AND DISCUSSION

A total of 113 insect species were identified in the sampled agroecosystems, 63 with phytophagous habit and 50 beneficial ones.

In the tree stratum 88 species were found to be associated (taking into consideration that 78 were present in both strata), 49 phytophagous (56%) and 39 beneficial (44%). The latter included: 23 predators, nine parasitoids, a pollinator, two mycophagous, three organic matter decomposers, and a coprophagous species. Besides the total, only 10 were present in the legume (four phytophagous and six beneficial) (table 1 Y 1a).

In spite of the remarkable amount of primary consumers detected, the literature refers that most of them do not cause severe affectations to leucaena (Suttie, 2007), with the exception of Heteropsylla cubana Crawford the main pest of this plant worldwide-, which was the cause of considerable loses up to 20 000 ha of the crop in Australia (Shelton, 1996) and brought about a 60% reduction of livestock production (Moog, 1992). In the case of Cuba, Barrientos et al. (1991) stated that it can produce damage of up to 95% in the apical portion of the branches.

With regards to other phytophagous insects, Empoasca sp. is reported to be able to damage other legumes, for example Cannavalia ensiformis L.; while Spissistylus rotundata and Spodoptera frugiperda affect alfalfa (Medicago sativa L.). In addition, the latter can be present in tropical kudzu (Pueraria phaseoloides (Roxb.) Benth.) and in different pasture and forage grasses, such as P. maximum, Brachiaria purpurascens (Raddi) Henr. and Sorghum vulgare Pers. In addition, Hortensia similis is found in the first two above-mentioned grasses, and Stenocoris tipuloides is found only in Guinea grass; as well as Remigia sp., which constitutes the main pest of pastures in the country (Bruner et al., 1975; Martínez et al., 2007).

Other insects found, which are also frequent and damage Glycine max L. (soybean) in grain and forage production are: Colaspis brunnea, Cryptocephalus marginicollis, Chalepus sanguinicollis, Loxa viridis, Dysdercus andreae, Jalyssus reductus, Coelioxys rufipes, S. tipuloides, Empoasca sp., S. rotundata and S. frugiperda, which have been reported in other pasture and forage plants; as well as Peregrinus maidis and Spodoptera sp., mentioned by Marrero (2004).

Among the captured phytophagous insects there are some which affect other economically important crops; for example: Mormidea pama, Oebalus pugnax and Paromius longulus can damage rice (Oryza sativa L.); Largus sellatus, Draeculacephala producta and P. maidis can be present in sugarcane (Saccharum spp.) and Spodoptera sp. in beans (Phaseolus vulgaris L.). On the other hand, S. frugiperda, considered the main pest of corn (Zea mays L.), also affects rice, beans and sugarcane; while H. similis is present in corn (Bruner et al., 1975; Suárez et al., 1989; Mestre et al., 2006; Martínez et al., 2007).

These elements contribute criteria of agricultural interest, because the use of leucaena as living fence, according to Veitia (2004), constitutes a physical barrier for immigrant phytophagous insects. Nevertheless, in agroforestry systems, when leucaena is associated to grasses and is neighbor to such crops as corn or rice, in spite of the influence of this tree as physical barrier, it can contribute to increase the dispersion of the different noxious organisms towards those crops, for which this is a practice that should be evaluated.

This means that the existing relation among the pest insects found in the sampled agroecosystems, with others integrated by plants from the same family or others that serve as host, is considered very important from the livestock production point of view, because it is necessary to take into consideration the neighboring character among crops to prevent the massive outbreaks of pests in established plantations as well as plantations to be promoted.

Regarding beneficial insects, the functional subgroups that act as biorregulators occupied an important percentage, such as predators (26%) and parasitoids (10%), among all the species associated to the tree; the most represented orders were Hymenoptera, Coleoptera and Diptera.

Nine species of the Himenoptera order were detected, belonging to ten of the most representative genera from the main families of entomophagous insects of this order in Cuba, according to the list provided by Vázquez (2006), which correspond to Brachymeria, Campsomeris, Conura, Enicospilus, Myzinum, Tetramonium, Tromatobia and Wasmannia. Likewise, nine genera were found from other orders of important entomophagous insect families, which coincided with the ones reported by the above-mentioned author, which represent different species; they are: Toxomerus (Diptera); Chilocorus, Coccinella, Cycloneda, Diomus, Scymnus (Coleoptera) ; Zelus (Hemiptera); Doru (Dermaptera) and Franklinothrips (Thysanoptera).

Among the coleopterans three of the most frequent ladybugs in all the provinces of the country are included, according to the prospections conducted since 1975 until 2004 by Milán et al. (2008): Cycloneda sanguinea limbifer, Coccinella maculata y Chilocorus cacti; the first two are, in turn, the most abundant, according to these authors. These predators were found associated to leafhoppers, among other phytophagous insects present in the sampled areas.

It must be emphasized that among the beneficial species detected the following were found: Tetramonium bicarinatum, predator of the immature stages of Remigia sp. and H. cubana; Zelus longipes, which likewise predates on the psyllid; in addition to parasitoids Enicospilus purgatus, Conura sp., the tachina fly (unidentified) and the predator Doru taeniatum, which are biological controls of the S. frugiperda larvae (Bruner et al., 1975; Maes and Hass, 2006; Martínez et al., 2007; Vázquez et al., 2008). E. purgatus is also a parasitoid of Remigia sp. (Vélez, 1985).

In the case of the undetermined species of the Eupelmidae family, it constitutes a parasitoid of spider and cockroach eggs, as well as L. viridis eggs, according to the direct observation of the authors of this work as well as H. Grillo (personal communication). With regards to Franklinothrips vespiformis, important predator of thrips, its action on Thris palmi Karny has been reported in soybean agroecosystems (Vázquez and Rodríguez, 1999; Marrero, 2004) and its presence can be related to that of Frankliniella tritici in the evaluated ecosystems. On the other hand, in the areas which produce that grain, Gassen (cited by Marrero, 2004) found that Condylostylus sp. is a predator of the larvae of leaf beetles; while such flies also predate on Auchenorrhyncha, according to Dely Rodríguez (personal communication).

It must be emphasized that the presence of this group of insects is a fundamental aspect in the maintenance of the biological balance among the species present in the crop, especially if it is taken into consideration that predators act, mostly, in an inspecific way, with which they contribute to reach the balance status in the agroecosystem, as well as the pollinators that favor the legume reproduction (Hughes, 1998).

Regarding the insects associated to the herbaceous stratum, 103 were found (considering the 78 which were found in both strata), from which 59 were classified as phytophagous (57%) and 44 as beneficial (43%), including: 23 predators, 13 parasitoids, a pollinator, four organic matter decomposers, a coprophagous and two mycophagous species. Twenty-five insects stood out (14 phytophagous and 11 beneficial) found only in this stratum (table 1 y 1a).

According to this result, it could be observed that in the agroecosystems where leucaena is associated to Guinea grass (due to the tillering condition of the latter) a larger number of habitats where insects are sheltered is generated, which is given mainly by the amount of vegetative and reproductive shoots produced by this plant in the vertical space. This association also brings about that the tree and herbaceous strata share a remarkable number of insects (78), which can be fond indistinctly in one or the other; this is due to the overlapping of the leaves and flower stems of Guinea grass with the lower branches of leucaena.

Such is the case of the species Remigia sp., S. frugiperda, Prosapia bicincta fraterna and H. similis, among the most relevant phytophagous insects, which are typical of this herbaceous vegetation, according to the criteria presented by Bruner et al. (1975), Barrientos (1984), Barrientos and Miret (1986) and Alonso and Docazal (1994), and with the exception of the third one, they shared the tree stratum.

Biorregulators, among the beneficial insects belonging to the orders cited as more representative in the tree stratum, reached the highest percentage in the herbaceous stratum: 22% in the case of predators and 13% of parasitoids. Specifically, species from the genera Conura, Pimpla y Rogas are included, which are reported among the most representative ten of the main entomophagous families of this order in Cuba (Vázquez, 2006). For example, Rogas sp. constitutes a parasitoid of the S. frugiperda pupae, for which it acquires importance as biorregulator within this agroecosystem (Martínez et al., 2007; Vázquez et al., 2008).

On the other hand, C. cacti, C. sanguinea limbifer, Diomus roseicollis and C. maculata, in addition to controlling H. cubana, can predate on the aphids Rhopalosiphum maidis (Fitch.) and Sipha flava Forbes, which are associated to different grasses, among them Guinea grass. The parasitoids Pimpla marginella and Campsomeris trifasciata regulate the populations of Omiodes indicata (Fabricius) (Vázquez et al., 2008) and Phyllophaga sp. (Bruner et al., 1975), respectively, which can be present in such herbaceous plants.

According to the results, it was considered that beneficial organisms, with their action, contributed to reduce the populations of pest insects in the agroecosystems, which coincides with the statements made by Ojasti and Dallmeier (2000). In addition, the mixture of herbaceous grasses with tree legumes in the agroforestry environment constitutes, from the agricultural point of view, a refuge source for an important number of the biorregulators included in this group.

The structure and function of the insect community in the two areas were concluded to show a relatively higher number of phytophagous insects as compared to the beneficial ones in both strata; but in the latter the predominance of biorregulators was determinant, because they are in charge of the regulating activity of the phytophagous activity and explain, partly, that the populations of noxious organisms of interest did not express the magnitude of the damage they can cause to the leucaena crop in the country, as in the case of H. cubana. Hence, to evaluate the utilization of the leucaena-Guinea grass association when the soil conditions and type of exploitation allow it is suggested, because with the balance attained with regards to the insects present, the duration of these plantations in time could be guaranteed.

 

ACKNOWLEDGEMENTS

The authors deeply thank the dedication of technician Yohania Sanabria Ramírez in performing the samplings and processing the insect samples.