The aim of this study was to identify egg parasitoids of Diatrea saccharalis F., sensu Guenée (Lepidoptera: Crambidae) in sugarcane in Tucumán, Argentina. We report a new host—parasitoid association of Trichogramma atopovirilia Oatman & Platner (Hymenoptera: Trichogrammatidae) attacking D. saccharalis and the first record of Trichogramma galloi Zucchi from Argentina. Additionally, Trichogramma pretiosum Riley was recorded in this survey.
El objetivo de este estudio fue identificar los parasitoides de huevos de Diatraea saccharalis F., sensu Guenée (Lepidoptera: Crambidae) en caña de azúcar en Tucumán, Argentina. Se reporta una nueva asociación hospedero parasitoide de Trichogramma atopovirilia Oatman & Platner (Hymenoptera: Trichogrammatidae) sobre D. saccharalis y es el primer registro de Trichogramma galloi Zucchi para Argentina. Además, se registró la presencia Trichogramma pretiosum Riley en este relevamiento.
The sugarcane borer, Diatraea saccharalis F., sensu Guenée (Lepidoptera: Crambidae), is the most damaging pest of sugarcane (Saccharum officinarum L.; Poales: Poaceae) in Argentina and in almost all other sugarcane producing countries in the New World (James 2004). Effectiveness of chemical control against this pest is limited because larvae develop inside the sugarcane stalks, which diminishes efficacy of the insecticides (Pereira et al. 2015). Taking into account successful experiences in Brazil and other countries, biological control seems to be the most effective approach to regulate populations of this pest (Botelho & Macedo 2002). In this regard, identification of natural enemies associated with the pest in an agroecosystem is a fundamental step (Zucchi 2002). Trichogramma Westwood (Hymenoptera: Trichogrammatidae) species are mainly associated with economically important lepidopterans (Zucchi et al. 2010), with around 210 species known worldwide (Pinto 2006). This genus has been used widely in biological control programs because of its efficiency, wide geographical distribution, and ease of breeding in the laboratory (Zucchi & Monteiro 1997).
In Argentina, few studies on the natural enemies of D. saccharalis have been conducted, all more than 70 yr ago. Box (1927) reported Telenomus alecto Crawford (Hymenoptera: Scelionidae) and Trichogramma sp. parasitizing D. saccharalis in Tucumán, and supposed the latter was T. minutum Riley. Jaynes (1933) recorded T. minutum in sugarcane borer eggs in Tucumán and Salta. Hayward (1943) recorded T. semifusca Blanchard but that name is unavailable. Unfortunately, no voucher specimens of these studies could be found. However, care must be taken about such information, considering that consistent male genitalia characters for species identification were employed only from the beginning of the 1970s. Previous records generally were not the result of taxonomic identification, i.e., they were based on the use of an available name found in the literature, without appropriate species confirmation (Querino & Zucchi 2007). Therefore, the goal of this study was to identify egg parasitoids of D. saccharalis on sugarcane crops from Tucumán, Argentina, undertaken as a first step to develop a biological control program.
Sampling of D. saccharalis egg clusters was conducted during the summer of 2013 at sugarcane commercial plots in Fronterita (Famaillá, 26.8123056°S, 65.0480000°W; 461 m), Luisiana (Cruz Alta, 27.0340833°S, 65.4731944°W; 401 m), and La Cruz (Burruyacú, 26.6561944°S, 64.8559444°W; 492 m) in Tucumán Province in Argentina. Sites were chosen attempting to include the diversity of climatic conditions prevailing in the region. The leaves and leaf sheaths with egg clusters were cut from the plant and taken in plastic cups to the Estación Experimental Agroindustrial Obispo Colombres laboratory, Tucumán, Argentina. Parasitized eggs were incubated in Petri dishes with wet absorbent paper and checked daily until adult parasitoid emergence.
Specimens obtained were kept in 70% ethanol until all were slide-mounted in Hoyer's medium, and later some were remounted in Canada balsam for permanent storage as vouchers. All emerging parasitoids were identified using specific keys (Pinto 1999; Querino & Zucchi 2011). Voucher specimens of Trichogramma species were deposited in the entomological collection of the Fundación e Instituto Miguel Lillo, San Miguel de Tucumán, Tucumán, Argentina (IMLA).
In total, 1,723 viable eggs of D. saccharalis (251 egg masses) were collected from the sugarcane fields in the course of this study, 44% of which were parasitized. The emerged specimens from La Cruz and Luisiana belonged to Trichogramma galloi Zucchi and Trichogramma pretiosum Riley, whereas all individuals from Fronterita were identified as Trichogramma atopovirilia Oatman & Platner.
Trichogramma galloi has not been recorded previously from Argentina. It was cited from many countries, mainly where sugarcane is cultivated (Zucchi et al. 2010). This species was first described by Zucchi (1988) from Brazil where it was obtained from D. saccharalis; all following records were from this host, except from Bolivia where it was identified parasitizing Diatraea rufescens Box eggs (Querino & Zucchi 2003). It is successfully used in augmentative biological control programs at São Paulo State in Brazil to control the sugarcane borer in 400,000 ha of sugarcane (Nava et al. 2009). During this study, T. galloi samples were obtained from 2 locations—16 males (IMLA) from eggs of D. saccharalis collected from Burruyacú (La Cruz) on 22-III-2013, and 12 males (IMLA) from eggs of D. saccharalis collected from Cruz Alta (Luisiana) on 25-IV-2013.
This is the first reported host association of T. atopovirilia with D. saccharalis on sugarcane. This parasitoid has often been cited from several lepidopteran pests in corn and soybean (Cañete & Foerster 2003). In Argentina, it was recorded attacking Spodoptera frugiperda Smith & Abbot (Lepidoptera: Noctuidae) on corn (Murúa et al. 2003). Currently, it is commercially reared in Brazil for biological control of S. frugiperda on corn (Pedrazzoli & Carvalho 2006). In the present study, T. atopovirilia samples (20 females, 31 males, IMLA) were obtained from D. saccharalis eggs collected from Famaillá (Fronterita) on 18-IV-2013.
Trichogramma pretiosum is the most widespread and important member of the genus in the New World and is present in all South American countries (Zucchi et al. 2010). This species is the most used parasitoid in biological control in many countries to control corn, cotton, sorghum, sugarcane, soybean, and tomato pests (Hassan 1994). Trichogramma pretiosum has been associated with about 240 hosts (Pinto 1999). During this study, we obtained T. pretiosum samples from 2 locations—7 males (IMLA) from D. saccharalis eggs collected from Burruyacú (La Cruz) on 22-III-2013, and 8 males (IMLA) from Cruz Alta (Luisiana) collected on 25-IV-2013.
All these species of Trichogramma are widely distributed on the American continent. In sugarcane, 8 Trichogramma species are associated with D. saccharalis in the Neotropical region, and 4 of them are known only from this host (Zucchi et al. 2010). It is important to note that T. alecto, which had previously been cited from Tucumán (Box 1927), was not found in the present study.
Knowledge of the natural presence of T. galloi, T. atopovirilia, and T. pretiosum in the sugarcane agroecosystem in Tucumán is an important finding for future prospective augmentative biological control programs in this state, because these species have shown a significant potential for use in many agricultural crops (Parra & Zucchi 2004). Studies about the bionomics of these species in Argentina are necessary.