The genus Trichogramma Westwood (Hymenoptera: Trichogrammatidae) includes insect egg parasitoids that are widely used throughout the world as control agents of pest insects. The aim of this study was to identify the species of Trichogramma naturally associated with the eggs of lepidopteran pests of the following agricultural and horticultural crops: collards, Brassica oleracea L. (Brassicales: Brassicaceae); papaya, Carica papaya L. (Capparales: Caricaceae); tomato, Lycopersicon esculentum Mill. (Solanales: Solanaceae); cassava, Manihot esculenta Crantz (Malpighiales: Euphorbiaceae); banana, Musa sp. L. (Zingiberales: Musaceae); passion fruit, Passiflora sp. Degener (Malpighiales: Passifloraceae); sugarcane, Saccharum sp. L. (Poales: Poaceae); and corn (maize), Zea mays L. (Poales: Poaceae); and an invasive species (Sodom's apple milkweed, Calotropis procera Aiton; Gentianales: Apocynaceae) in the semiarid region of Minas Gerais, Brazil. We report natural parasitism by Trichogramma in eggs of Agraulis vanillae vanillae (L.) (Lepidoptera: Nymphalidae), Antichloris eriphia F. (Lepidoptera: Arctiidae), Danaus sp. (L.) (Lepidoptera: Nymphalidae), Diatraea saccharalis F. (Lepidoptera: Crambidae), Erinnyis ello L. (Lepidopera: Sphingidae), and Protambulyx strigilis L. (Lepidopera: Sphingidae). In total, 2,242 specimens of Trichogramma were obtained, belonging to the species T. pretiosum Riley, T. manicobai Brun, Moraes & Soares, T. marandobai Brun, Moraes & Soares, and T. galloi Zucchi. These species of Trichogramma may be candidates for biological control programs of lepidopteran pests in the semiarid region of Minas Gerais and in other semiarid regions.
The genus Trichogramma Westwood (Hymenoptera: Trichogrammatidae) has the largest number of species in the family Trichogrammatidae. Among its 210 species (Pinto 2006), 41 have been reported in South America and 26 in Brazil (Zucchi et al. 2010). Many species of Trichogramma are used worldwide for the biological control of lepidopteran pest species (Smith 1996; Mills 2010) through inundative releases into millions of hectares of a wide variety of crops (Li 1994; Parra & Zucchi 2004; Pizzol et al. 2012).
Some favorable characteristics of Trichogramma species have led to the widespread use of this genus in integrated pest management programs. These characteristics include the ease of rearing on alternative hosts (Parra 2010a; Díaz et al. 2012); parasitism of the pest's egg stage and before the pest can damage crops (Ulrichs & Mewis 2004; Gardner et al. 2011); highly aggressive parasitism of various species of lepidopteran pests (Botelho 1997); and a wide geographic distribution (Pinto 2006).
The key to the success of Trichogramma-based biological control is to use adequate native species, if possible, to reduce the population of specific pests (Hassan 1994), as native parasitoids are well adapted to their natural environments. In light of this premise, population surveys of pest insects and their natural enemies provide information about the local fauna and help prevent a leading cause of failure of biological control programs, namely, lack of knowledge of existing populations (Hassan 1994; Smith 1996; Pinto 1999).
The taxonomy of Trichogramma is fundamentally important for the maintenance of these natural enemies in agricultural areas and for the establishment of integrated pest management programs that use these wasps as agents of biological control. Few studies on the native species of Trichogramma in the State of Minas Gerais, Brazil, have been published (Murta et al. 2008; Zanuncio et al. 2009; Macedo-Reis et al. 2013). The northern region of Minas Gerais has a semiarid climate and a diverse range of agricultural crops, and the composition of its native fauna is not completely known.
The objective of this work was to identify the species of Trichogramma that are naturally associated with eggs of pest lepidopterans on 8 agricultural crop species and 1 invasive species in the semiarid region of Minas Gerais, Brazil. The 9 species were as follows: collards, Brassica oleracea L. (Brassicales: Brassicaceae); papaya, Carica papaya L. (Capparales: Caricaceae); tomato, Lycopersicon esculentum Mill. (Solanales: Solanaceae); cassava, Manihot esculenta Crantz (Malpighiales: Euphorbiaceae); banana, Musa sp. L. (Zingiberales: Musaceae); passion fruit, Passiflora sp. Degener (Malpighiales: Passifloraceae); sugarcane, Saccharum sp. L. (Poales: Poaceae); and corn (maize), Zea mays L. (Poales: Poaceae); and an invasive species (Sodom's apple milkweed, Calotropis procera Aiton [Gentianales: Apocynaceae]). The overall aim of this study was to provide information for the development of pest management initiatives in the region.
Materials and Methods
Random qualitative collections were made in the municipalities of Jaíba, Janaúba, Nova Porteirinha, and Porteirinha, located in the semiarid region of the state of Minas Gerais, Brazil. The vegetation at these locations consists of transition areas between the Caatinga and Cerrado biomes. The vegetation observed in this ecotone is a typical Dry Forest (Drummond et al. 2005), also known as Deciduous Seasonal Forest. Dry Forests are characterized by a predominantly deciduous stratum and are observed in areas with 2 well-defined seasons, namely, a rainy season and an extended dry season (Veloso et al. 1991).
The collections were made by visual inspection for eggs or egg masses of pest lepidopterans on 9 plant species. The plants and pest species were as follows: collards - Ascia monuste orseis (Latreille) (Lepidoptera: Pieridae); Sodom's apple - Danaus sp. (L.) (Lepidoptera: Nymphalidae); papaya - Protambulyx strigilis L. (Lepidoptera: Sphingidae); cassava - Erinnyis ello L. (Lepidoptera: Sphingidae); banana - Antichloris eriphia F. (Lepidoptera: Arctiidae); passion fruit - Agraulis vanillae vanillae (L.) (Lepidoptera: Nymphalidae) and Dione juno juno (Cramer) (Lepidoptera: Nymphalidae); sugarcane - Diatraea saccharalis F. (Lepidoptera: Crambidae); tomato - Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae); and corn - Spodoptera frugiperda Smith & Abbot (Lepidoptera: Noctuidae). The collections were made between Dec 2007 and Oct 2008. The agricultural crop species to be sampled were chosen according to their economic importance to the region and their availability during the sampling period.
The selected plants were inspected for a period of 20 min; when lepidopteran eggs or egg masses were observed, they were collected along with part of the inspected plant. The collected eggs or egg masses of these lepidopterans were stored in labeled paper bags and transported to the Entomology Laboratory at the Montes Claros State University (UNIMONTES) campus in the city of Janaúba, Minas Gerais.
The collected eggs or egg masses of pest insects were quantified and each individual egg mass was considered to be an egg unit. These eggs were stored in glass containers covered with plastic wrap and were maintained in the laboratory under room conditions. Observations were made on a daily basis until the lepidopteran larvae or the parasitoid wasps had emerged. The percentage of parasitism of each host insect species was calculated as the ratio of parasitized eggs or egg masses to the total number of collected eggs or egg masses (number of parasitized eggs × 100 / total number either of collected individually laid eggs or of collected egg masses).
The emerged parasitoids were counted and sexed, and the males were preserved in 70% ethanol for species identification. The females were preserved in 90% ethanol. Species identification of Trichogramma is based on the morphological characteristics of males. Therefore, the collected females were identified only if they had emerged together with males from the same host egg. In these situations, all individuals were assumed to belong to the same species. The identification to species was not performed when only females emerged.
The specimens of Trichogramma were mounted in Hoyer's medium on microscope slides (Querino & Zucchi 2002, 2011). Species identification was based on characteristics of the genitalia, antennae, and wings of males, using an illustrated identification key for Trichogramma species of Brazil (Querino & Zucchi 2005). The collected specimens were deposited in the collection of the Entomology Laboratory at UNIMONTES.
In total, 2,242 specimens of Trichogramma (1,712 females and 530 males) were obtained from eggs of lepidopterans collected on the above mentioned agricultural crops and on the 1 invasive species in Minas Gerais State (Table 1). Four species of the parasitoid wasps were identified, i.e., T. pretiosum Riley; T. manicobai Brun, Moraes & Soares; T. marandobai Brun, Moraes & Soares; and T. galloi Zucchi. The species T. pretiosum was obtained from the eggs of all sampled species of Lepidoptera that were found to be hosts to parasitoids, with the exception of A. eriphia on banana in which case the parasitoid species found could not be identified.
Natural parasitism by Trichogramma was observed in the lepidopteran eggs collected on 6 plant species in the sampled agricultural ecosystems (Table 1), namely, passion fruit, banana, Sodom's apple, sugarcane, cassava, and papaya. Eggs of A. vanillae vanillae, A. eriphia, Danaus sp., D. saccharalis (egg masses), E. ello, and P. strigilis, respectively, were collected from these plant species. In contrast, no eggs of A. monuste orseis and T. absoluta or egg masses of D. juno juno and S. frugiperda were found on collards, tomato, passion fruit, and corn, respectively.
The largest number of Trichogramma species was obtained from eggs of E. ello on cassava (Table 1). We observed T. pretiosum, T. manicobai, and T. marandobai in association with this host. Two species, T. galloi and T. pretiosum, parasitized the same egg mass of D. saccharalis on sugarcane. The lepidopteran A. vanillae vanillae was parasitized by T. pretiosum on passion fruit. On papaya, eggs of P. strigilis were parasitized by T. pretiosum and T. manicobai. Both of these Trichogramma species parasitized eggs of Danaus sp. on Sodom's apple milkweed. This is the first report of parasitism by T. manicobai of eggs of Danaus sp. and P. strigilis. Trichogramma specimens that emerged from eggs of A. eriphia collected on banana were not identified because of the absence of males.
Plant species sampled for assessment of parasitism by Trichogramma wasps in eggs of pest lepidopterans in the semiarid region of the state of Minas Gerais, Brazil, during Dec 2007 to Oct 2008.
Percentage of natural parasitism of pest lepidopteran eggs by Trichogramma wasps in the semiarid region of the state of Minas Gerais, Brazil, during Dec 2007 to Oct 2008.
The number of parasitoid adults that emerged per egg of the host insects ranged from 5.33 to 17.08 (Table 1). An average of 24.92 parasitoids emerged per egg mass of D. saccharalis. The average number of Trichogramma adults obtained from eggs of D. saccharalis was assessed per egg mass. On average, 11 eggs of D. saccharalis were counted per egg mass of this host pest.
In the semiarid region of Minas Gerais, the percentage of natural parasitism of individual eggs of species that lay each egg individually ranged from 6.3% for A. eriphia on banana to 43.5% for E. ello on cassava (Table 2). However, in the same region, 100% of the egg masses of D. saccharalis on sugarcane were parasitized (Table 2).
Parasitism by Trichogramma was observed in fields planted with fruit and vegetable crops in Minas Gerais State, as had been observed in other studies in Eucalyptus-growing areas (Zanuncio et al. 2009; Macedo-Reis et al. 2013). Natural parasitism of pest Lepidoptera eggs by Trichogramma species was verified in 6 of 9 of the plant species in the sampled agricultural ecosystems. This result shows the importance of Trichogramma species in the natural biological control of Lepidoptera pests (Zanuncio et al. 2009). In addition, the mass rearing and the use of Trichogramma for the biocontrol of host-pests began in Brazil over 30 yr ago with excellent results for several crops (Parra 2010b).
Trichogramma pretiosum emerged from the eggs of the largest number of pest lepidopteran species. This result can be explained by the generalist behavior of T. pretiosum (Li 1994), which is widely distributed in all countries of South America (Zucchi et al. 2010) and has been reported in association with over 240 host species (Pinto 1999). Among the species of lepidopterans reported here, A. vanillae vanillae, Danaus sp., D. saccharalis, and E. ello had already been reported as hosts of T. pretiosum; however, this is the first report of T. pretiosum as a parasitoid of P. strigilis.
A substantial number of Trichogramma species was obtained from eggs of E. ello on cassava. In addition, T. atopovirilia Oatman & Platner and T. demoraesi Nagaraja had already been reported in association with E. ello in Brazil (Zucchi et al. 2010). The parasitism of P. strigilis and Danaus sp. eggs by T. manicobai was unknown before this study. Prior to this study, the lepidopteran E. ello was the only reported host of T. manicobai (Zucchi et al. 2010).
The emergence of T. pretiosum and T. galloi from the same egg mass of D. saccharalis in sugarcane was verified. The species T. galloi is the most widely used species in this agricultural crop, and is released over about 300,000 ha of sugarcane each year in order to control the sugarcane borer (Parra 2010b). In addition to these 2 species, other species of Trichogramma have already been associated with D. saccharalis, namely, T. dissimilis Zucchi, T. distinctum Zucchi, and T. jalmirezi Zucchi (Zucchi & Monteiro 1997). Trichogramma pretiosum and T. galloi show great potential for use in biological control on several crops in Brazil, and their ease of rearing in the laboratory enhances their potential for even wider use as natural enemies (Parra & Zucchi 2004).
The variation in number of Trichogramma specimens obtained per egg or egg mass of pest lepidopterans, as well as the varying percentages of parasitism, may be related to the specific morphological characteristics of each host egg (Sa & Parra 1994), the size and age of the host eggs (Beserra et al. 2002; Brotodjojo & Walter 2006), and the quality of the eggs for parasitoid development (Roriz et al. 2006). Parasitism rates by Trichogramma parasitoids, which are usually recorded in the field, may often underestimate the total mortality induced in the host populations (Tabone et al. 2010).
The natural parasitism of eggs of lepidopterans by Trichogramma species in various highly profitable agricultural and horticultural crops and the substantial percentages of biological control achieved against some species of pest lepidopterans in northern Minas Gerais provide important information about the interactions between natural enemies and host insects and plants in this region. In addition, the natural occurrence of Trichogramma suggests that these parasitoids may be well adapted to this environment. Consequently, the species of this genus may be considered as candidates for inclusion in integrated pest management programs especially in arid and semiarid tropical and subtropical regions.
The authors express heartfelt gratitude to the Minas Gerais Research Foundation (FAPEMIG) and to the National Council for Scientific and Technological Development (CNPq) for financial support. We acknowledge Ms C. Jonny Burga, who reviewed the Spanish spelling in this manuscript.