4 Ph.D. Professor Universidade Federal do Espírito Santo, Brazil pratissoli@cca.ufes.br ]]>
Received: 21-jan-2011 - Accepted: 21-jul-2011
Abstract: Lepidoptera defoliators are important pests of Eucalyptus. This research aimed to evaluate the potential of Trichogramma acacioi and Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) to control the eucalyptus defoliator Oxydia vesulia (Lepidoptera: Geometridae). Biological parameters and parasitism rate of Trichogramma on eggs of O. vesulia were evaluated under laboratory conditions. Trichogramma pretiosum did not parasitized eggs of O. vesulia but more than 93% of T. acacioi females parasitized eggs of this defoliator, showing its potential for the biological control of this Lepidoptera.
Resumen: Los lepidópteros defoliadores son importantes plagas de Eucalyptus. El objetivo de este trabajo fue evaluar el potencial de Trichogramma acacioi y Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) para controlar el defoliador del eucalipto Oxydia vesulia (Lepidoptera: Geometridae). Los parámetros biológicos y la tasa de parasitismo de Trichogramma en huevos de O. vesulia fueron evaluados en condiciones de laboratorio. Trichogramma pretiosum no parasitó esta especie, pero más de 93% de las hembras de T. acacioi presentaron parasitismo en los huevos de este defoliador, mostrando su potencial para el control biológico de este lepidóptero.
Palabras clave: Parasitoide de huevos. Control biológico. Eucalyptus. Lepidoptera.
Introduction
Lepidoptera defoliators are found in Eucalyptus plantations and their importance is increasing due to frequent outbreaks and damage (Oliveira et al. 2008; Pereira et al. 2008). This group includes species of the genus Oxydia (Lepidoptera: Geometridae) which have been collected in population outbreaks in the Brazilian States of Minas Gerais, São Paulo (Zanuncio et al. 1994), Maranhão (Zanuncio et al. 1992), Goiás (Alves et al. 1994) and Bahia (Santos et al. 2002). Outbreaks of these species have been controlled with different methods, but especially with chemical insecticides which can have negative impact on the environment (Zanuncio et al. 1994; Zanuncio et al. 2001; Oliveira et al. 2003). Therefore, there is a need to develop alternative control methods for this kind of pest (Zanuncio et al. 1991). The release of Trichogramma species, which have been widely used in many crops, represents one of the techniques that have shown good results to control pest, especially in species of Lepidoptera (Bueno et al. 2009).
Some species such as Trichogramma demoraesi Nagaraja, 1983, Trichogramma soaresi Nagaraja, 1983, Trichogramma manicobai Brun, Moraes & Soares, 1984, Trichogramma caiaposi Brun, Moraes & Soares 1984, Trichogramma maxacalii Voegelé and Pointel, 1980, Trichogramma acacioi Brun, Moraes & Soares, 1984 and Trichogramma pratissolii Querino and Zucchi, 2003 are recorded occurring in eucalyptus plantations (Oliveira et al. 2003; Soares et al. 2007; Vianna et al. 2007). But it is necessary to evaluate the interaction between these parasitoids and the host target because species of Trichogramma have a great variation in behavior and preference (Bueno et al. 2009). For this reason, the objective of this research was to evaluate the ability of T. acacioi and Trichogramma pretiosum Riley, 1879 (Hymenoptera: Trichogrammatidae) to parasitize eggs of Oxydia vesulia (Cramer, 1779) (Lepidoptera: Geometridae).
The biological characteristics of T. acacioi and T. pretiosum were studied using eggs of O. vesulia obtained from adults originating from caterpillars collected in a eucalyptus plantation and reared with Eucalyptus cloeziana F. Muell.. The experiment was carried out at 25±1ºC, 75±10% relative humidity and 14h photoperiod. Twentyfve fresh eggs of O. vesulia were glued onto a piece of blue cardboard (3.5 x 0.5cm) with Arabic gum (30% diluted) and were offered to the parasitoids on the same day. Each cardboard was placed in a glass tube with one parasitoid female with maximum age of 24h and honey droplets were offered as food. The cardboard was removed from the tubes after 24 hours and kept in a plastic bag under the same conditions as described above. Fifteen replicates were done for each parasitoid species. The percentage of females that parasitized, the parasitism rate (number of eggs parasitized/number of eggs in the cardboard), embryonic period (between egg to adult emergence), emergence rate (eggs with a hole made were counted to evaluate), number of individuals/egg, sex ratio (number of females/number of females + males) and longevity of female offispring were evaluated.
Females of T. pretiosum did not parasitize eggs of O. vesulia although T. acacioi parasitized 93.3% of those (Table 1). Some factors that may explain the host rejection by the parasitoid are size, format and texture of the host eggs (Schmidt 1994; Oliveira et al. 2000; Moreira et al. 2009) and these factors can also affect the behavior of Trichogramma and their capacity to parasitize a specific host (Schmidt and Smith 1987). In the feld, host eggs of these two parasitoid species may have a different size. In our study, the strain of T. pretiosum was collected in areas which tomato was grown, parasitizing eggs of Tuta absoluta (Meyrick, 1917) (Lepidoptera: Gelechiidae) while T. acacioi were collected in arboreal environments, with avocado orchards occurring in Nipteria panacea Thierry-Mieg, 1892 (Lepidoptera: Geometridae) eggs. Probably O. vesulia eggs have sizes more similar to those accepted by T. acacioi than by T. pretiosum.
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The parasitism rate of T. acacioi on eggs of O. vesulia was around 15%, lower when compared to the performance of this parasitoid on eggs of Anagasta kuehniella Zeller, 1879 (Lepidoptera: Pyralidae) and Sitotroga cerealella (Olivier, 1789) (Lepidoptera: Gelechiidae) (Pratissoli et al. 2009). However, it is important to emphasize that the size of the eggs are different, being the O. vesulia eggs bigger than those from the factitious host. Bueno et al. (2009) reported that the size of the egg can infuence the number of eggs laid per female of Trichogramma. The results found in this work showed a larger number of individuals produced per egg of O. vesulia than those from alternative host. On the other hand, in the same host, the parasitism by different species of Trichogramma can vary, because the number of eggs of O. vesulia parasitized by T. acacioi was higher than that by T. maxacalii (Oliveira et al. 2003).
The parasitism it is an important factor in the selection of the species or strain of parasitoids, and in the feld this biologic characteristic can be especially important to determine the best species (Bueno et al. 2009). This higher parasitism indicates that T. acacioi should present better potential in controlling O. vesulia. The viability, sex ratio, number ofindividuals per egg, female longevity and duration of the embryonic period found to T. acacioi (Table 1) was similar to those of T. maxacalii on eggs of this defoliator (Oliveira et al. 2003).
Trichogramma acacioi may be used with T. maxacalii to control eggs of the Lepidoptera defoliator O. vesulia. Additionally, further studies should be developed to define the potential of these parasitoids as biological control agents of Lepidoptera defoliators of Eucalyptus species.
Acknowledgments
To Conselho Nacional de Desenvolvimento Científico e Tecnológico - CNPq
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