José M.M. Pereira ¹ , Teresinha V. Zanuncio ¹ , José C. Zanuncio ¹ * and Angelo Pallini ¹

1 Department of Animal Biology, Federal University of Viçosa, 36571-000, Viçosa, Minas Gerais; Brazil. *Author for correspondence. Fax: +5531-3899-2537. E-mail: zanuncio@mail.ufv.br

Recibido 25-X-1999. Corregido 15-XI-2000. Aceptado 25-II-2001.

Key words: Lepidoptera pests, light traps, Eucalyptus urophylla, faunistic analysis, frequency, constancy.

Brazil is the fourth country in the world on homogeneous forest plantations (Cottle et al. 1990) with an area over four million hectares (Ohmart and Edwards 1991). The State of Minas Gerais in the East Region of Brazil presents an area of 1 535 750 ha of plantations with eucalyptus species (Brandão 1997). According to Siqueira (1990) such reforestation constitutes an important source of wood for industries in Brazil, which use 39 % of the total volume of wood consumed from cultivated areas. Hence, this sector represents an important part of the Brazilian economy. During the first years of the 1990s approximately 5 % of the Brazilian Gross National Product originated from the forest sector (Rezende et al. 1996).

One factor that constrains increase in eucalyptus production is the damage caused to insects in the field. Defoliator insects such as lepidopterous, coleopterous and leaf-cutting ants can cause significant losses to forest productivity in Brazilian reforested areas but very little is known about natural factors that regulate their populations (Bragança et al. 1998a, b). Therefore it is essential to identify herbivore species, their level of damage and the factors that could affect their populations in eucalyptus plantations (Zanuncio et al. 1998b). The importance of phytophagous insects is due to the fact that they can affect plants in different ways such as killing them, reducing their growth, and weakening plants, which will turn them more susceptible to pathogens (Coulson and Witter 1984).

Defoliating Lepidoptera species associated with eucalyptus are categorized according to their damage to the plantation. In southeastern Brazil, Zanuncio et al. (1994) described the major defoliator lepidopterous occurring in the area, ranking them in primary and secondary pests after extensive studies on outbreaks reported in the area (Zanuncio and Lima 1975, Santos et al. 1982, Soares and Moraes 1982, Zanuncio et al. 1990, Zanuncio et al. 1992).

Light traps are being used for most entomofaunistic studies of Lepidoptera pests in reforested areas of Brazil. According to Menezes et al. (1986), the occurrence and population fluctuation of pests are essential in integrated pest management programs because they can show where pests occur and also when their populations fluctuate during the year. The objective of this research was to use light traps to monitor and to identify defoliator lepidopterous pests in plantations of Eucalyptus urophylla in the region of "Três Marias", State of Minas Gerais, Brazil.

From June 1989 to June 1994 lepidopterous pests were collected in five blocks of E. urophylla plantations about two years old at the beginning of this study in the region of "Três Marias", State of Minas Gerais, Brazil (18º 10’ 35’’ S, 45º 00’ 10’’ W), altitude of 590 m. Mean annual temperature and rainfall of this region was 22 ºC and 1 200 mm, respectively.

Insects were collected every two weeks with five black light traps installed at 2 m above ground as proposed by Ferreira and Martins (1982). Insects collected were screened and separated by size and conditioned in entomological blankets labelled with day, month, year, number of the trap and place of collection. Thereafter, they were sent to the Department of Animal Biology at the Federal University of Viçosa, State of Minas Gerais, Brazil where they were sorted, mounted, identified and separated in groups of importance to eucalyptus plantations (Zanuncio et al. 1994) as following: group I- species considered primary pests; group II- species considered secondary pests; group III- species considered without defined importance to eucalyptus plantations, and group IV– non identified species.

Faunistic analysis of species from groups I and II were made by frequency (Bodenheimer 1955) and constancy (Dajoz 1974) indexes. ]]>

From June 1989 to June 1994 a total of 19 502.23 individuals of Lepidoptera per light trap were collected in the study area (Table 1). Number of species collected increased annually, except during the second year. At the fifth year, there were collected 488 species against 262 species collected in the first year (Table 1), which represents an increase of 1.86 times during the study period. Primary (group I) and secondary (group II) pests together totalized lower numbers of species than groups III and IV along the years. However, primary pests had more individuals collected per light trap, followed by the secondary ones, than groups III and IV when considering the number of individuals collected per light trap per species (Table 1).

Table 1

 
Although highest number of population peaks of primary pests were recorded from February to June (Fig. 1), highest numbers of individuals of these pests occurred in different months during the five years with population peaks of Eupseudosoma aberrans (Lepidoptera: Arctiidae) being recorded in the second year, Stenalcidia grosica (Lepidoptera: Geometridae) in the third year, and Iridopsis subferaria (Lepidoptera: Geometridae) in the fifth year (Table 2). From the secondary pest group, Idalus admirabilis, responsible for the largest number of individuals of this group (Table 2), presented population peaks from January to March of the first year (Table 3).

Table 2

Annual number of individuals per light trap of Lepidoptera primary and secondary pests, collected in the ]]> region of "Três Marias", State of Minas Gerais, Brazil. June 1989 to June 1994

- not collected

pests presented larger numbers between January and March (Fig. 2). Secondary pests such as I. admirabilis, Lepidokirbya vittipes (Lepidoptera: Arctiidae) and Misogada blerura (Lepidoptera: Notodontidae) showed population peaks in similar periods as the primary ones (Table 3).

Table 3

Annual number of individuals per months of higher occurrence of Lepidoptera primary and secondary pests,
collected in the region of "Três Marias", State of Minas Gerais, Brazil. June 1989 to June 1994

]]>

* x = Species constant y = Species acessory z = Species acidental

- = not collected

Table 5

Annual number of individuals of Lepidoptera primary and secondary pests of Eucalyptus, collected in the region of "Três Marias", State of Minas Gerais, Brasil June 1989 to June 1994

 
Discussion

Increasing number of lepidopterous species from the first to the last year of study (Table 1) could indicate that lower input on weed control with age increase of the eucalyptus plants probably allow an increase in vegetation diversity in the area, which could in turn permit a partial recovery of the insect fauna in ecosystems formed by plantations of eucalyptus species (Zanuncio et al. 1998a, b). Besides, the similar number of pest species during the study period shows that in the first years of the eucalyptus plantations these species which are, probably, reproducing in native plants can adapt to the new ecosystem formed by plantations. Low number of individuals per species of groups III and IV could indicate that they do not feed on eucalyptus trees but they are probably associated to vegetation under these trees or even that they come from areas surrounding the eucalyptus plantations. On the other hand, high number of individuals per species of group I show that they can feed and reproduce on eucalyptus trees. Largest number of individuals of primary pests from April to July and of secondary ones from January to March agrees with other reports on lepidopterous pests of eucalyptus (Balut and Amante 1971, Moraes and Soares 1981, Santos et al. 1985, Pereira et al. 1994). Such high numbers of primary pest individuals are usually associated to periods of low temperature and low rainfall while the opposite happens for many secondary ones (Zanuncio et al. 1993). Most species of this last group pupate in the soil because they need humidity for adult emergency, and this may explain their largest occurrence during periods of high rainfall. Additionally, several secondary pest species, which do not pupate in the soil, present population peaks in similar periods as the primary species.

The year by year alternation of species with the highest annual frequency shows low risk of outbreaks occurrence for the same species in the area during more than one consecutive year. This could suggest that after reaching a population peak, numbers of individuals of each species are reduced by natural factors such as predators or parasitoid insects and diseases, thereby maintaining these pests at low population levels during several consecutive years (Zanuncio et al. 1994). On the other hand, such decrease on the population leaves the habitat available for another species to show a population increase. Some species were classified as constant (Table 3) in a year before their population peak, which shows that such population increase starts in the previous year when these species show a gradual increase of their number of individuals.

The predominance of four primary and one secondary pest species shows that even though there is an abundance of food supply for these pests in eucalyptus plantations their populations do not increase steadily probably due to biotic or abiotic factors which need to be better studied (Zanuncio et al. 1996, Torres et al. 1996/1997, Saavedra et al. 1997). The understanding of such factors could be used in programs of integrated pest management of defoliator Lepidoptera in eucalyptus plantations. The number of primary pest increased from seven to 12 species from the first to the fifth collecting period, showing that some of these species may prefer to feed on older eucalyptus trees while other are able to feed on these trees during all its growing stage which is usually about seven years in Brazil.

Some ecological aspects of defoliating caterpillars found in the area are important when considering an integrated pest management program. For example, caterpillars of S. grosica, the primary pest with largest number of individuals, besides those of I. subferaria are found on eucalyptus leaves while its pupation occur in organic debris over the superficial layer of the soil (Santos et al. 1998). For this reason, the detection of those species, in the field can be made by counting their caterpillars per branch of eucalyptus or removing the organic layer on the top of the soil near to eucalyptus plants, aiming to count number of their pupae per square meter. In a similar way, number of caterpillars of E. aberrans could be either expressed as number per leave or per branch of eucalyptus. Alternatively, number of pupae could be evaluated by area of eucalyptus trunk where this species presents its pupal phase.

Population monitoring of primary and secondary lepidopterous pests in this area should be made from January to May when most of population peaks of these pest species occur. Such monitoring can be made with different methods, including use of a cheese cloth under the eucalyptus trees for collecting falling caterpillars. Light traps or even counting numbers of caterpillars per eucalyptus branches could be used to detect population of defoliator caterpillars in more limited and smaller areas. These practices could reduce control costs and damage if such pests are found before reaching outbreak conditions.

We thank CNPq/Brasília/Brazil, CAPES / Brasília / Brazil, FAPEMIG / Belo Horizonte / Brasil for financial support, and the research team of the Department of Animal Biology-Entomology at the Federal University of Viçosa for valuable discussions.

La ocurrencia de plagas primarias y secundarias del orden Lepidoptera fue estudiada desde junio de 1989 hasta junio de 1994 en plantaciones de Eucalyptus urophylla, localizadas en la region de Tres Marias, Estado de Minas Gerais, Brasil. Durante este periodo, las colectas de lepidópteros fueron realizadas quincenalmente usando cinco trampas de luz. Después de cinco años de recolección la media total por trampa fue de 13 387 especímenes de plagas primarias y 812 de plagas secundarias, pertenecientes a 12 y 15 especies diferentes respectivamente. Las cuatro especies de plagas primarias más comunes fueron Stenalcidia grosica (Geometridae), Iridopsis subferaria (Geometridae), Eupseudosoma aberrans (Arctiidae) e Psorocampa denticulata (Notodontidae) con media de 5 450; 2 162; 2 436 y 1 458 especímenes, respectivamente. A su vez, la plaga secundaria más comun entre las colectadas fue Idalus admirabilis (Arctiidae) con media de 652 especímenes. Por outro lado, durante la estación seca (marzo a julio) fue la época más adecuada para la presencia de plagas primarias, mientras que durante la época lluviosa (enero a marzo) fue la más apropriada para las plagas secundarias.

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