SEARCHING AND PARASITISM OF Diatraea saccharalis (LEPIDOPTERA: CRAMBIDAE) BY Trichospilus diatraeae (HYMENOPTERA: EULOPHIDAE)

Búsqueda y parasitismo de Diatraea saccharalis (Lepidoptera: Crambidae) por Trichospilus diatraeae (Hymenoptera: Eulophidae)

ELIZANGELA LEITE VARGAS¹, M.Sc.; FABRICIO FAGUNDES PEREIRA¹, Ph. D.; DANIELE FABIANA GLAESER², Ph. D.; VANESSA RODRIGUES FERREIRA CALADO¹, M.Sc.; FABIANA GARCIA DE OLIVEIRA¹, M.Sc; PATRIK LUIZ PASTORI³, Ph. D.

¹Universidade Federal da Grande Dourados, rodovia Dourados-Ithaum, Km 12, CXP: 533, Zip Code: 79804-970, Dourados, MS, Brasil. ²Embrapa Agropecuária Oeste, CXP: 661, Zip Code: 79804-970, Dourados, MS, Brasil. ³Universidade Federal do Ceará, Departamento de Fitotecnia, Zip Code: 60.356-000, Fortaleza, CE, Brasil. Corresponding autor: Elizangela Leite Vargas, elileitevargas@gmail.com.

Presentado el 19 de diciembre de 2012, aceptado el 14 de abril de 2013, correcciones el 22 de mayo de 2013.

ABSTRACT

The ability of Trichospilus diatraeae Cherian and Margabandhu, 1942 (Hymenoptera: Eulophidae) to search and parasitize Diatraea saccharalis (Fabricius, 1794) (Lepidoptera: Crambidae) pupae in sugarcane stalks was evaluated. To analyze the ability for search and parasitism were used stalks of sugarcane (20 cm) where it was introduced a pupa of D. saccharalis (T1); a pupa and a caterpillar (T2) or a pupa and fecal matter (T3). Each stalk was placed in a transparent plastic bottle with 21 females of T. diatraeae. These pupae were isolated, after 72 h, in glass tubes at 25 ± 2 °C, 70 ± 10 % relative humidity, 14:10 light/dark. The experiment was developed in an entirely casualized design with three treatments and 12 repetitions. Percentage of D. saccharalis pupa parasitized by T. diatraeae was 50.00 %, 83.33 % and 16.66 % in the T1, T2 and T3, respectively (X² = 3.896, p= 0.04). The presence of D. saccharalis caterpillars favored searching and parasitism of this host.

Keywords: biological control, host location, parasitoid.

RESUMEN

Palabras clave: control biológico, localización hospedero, parasitoide.

RESUMO

A capacidade de Trichospilus diatraeae Cherian e Margabandhu, 1942 (Hymenoptera: Eulophidae) para procurar e parasitar pupas de Diatraea saccharalis (Fabricius, 1794) (Lepidoptera: Crambidae) em colmos de cana-de-açúcar foi avaliada. Para analisar a capacidade de busca e parasitismo foram usados colmos de cana-de-açúcar (20 cm), onde foi introduzida uma pupa de D. saccharalis (T1); uma pupa e uma lagarta (T2) or uma pupa e resíduo fecal (T3). Cada colmo foi colocado em uma garrafa plástica transparente com 21 fêmeas de T. diatraeae. Essas pupas foram retiradas dos colmos após 72 h, e colocadas em tubos de vidro a 25 ± 2 ° C, 70 ± 10 % de umidade relativa e fotofase de 14 h. O experimento foi desenvolvido em delineamento inteiramente casualizado, com três tratamentos e 12 repetições. A porcentagem de pupas de D. saccharalis parasitadas por T. diatraeae foi de 50,00 %, 83,33 % e 16,66 % em T1, T2 e T3, respectivamente (X²= 3,896, p = 0,04). A presença de lagartas de D. saccharalis favoreceu a busca e parasitismo deste hospedeiro.

Palavras-chave: controle biológico, localização de hospedeiro, parasitoide.

INTRODUCTION

Adult female parasitoids respond to semiochemicals in the micro-habitat to find host pupae (Pinto et al., 2007; Fontana et al., 2011). These compounds are released from plants infested by herbivores and/or from fecal matter of these insects which are detected by parasitoid receptors (Fatouros et al., 2007; Dicke et al., 2009; Girling et al., 2011; Hegde et al., 2011). The efficiency of parasitoids depends on its ability to detect hosts in the field natural conditions (Silva-Torres et al., 2009), although it lay be reduced in absence of hosts at right developmental stages for parasitism (Hausmann et al., 2005). The capacity parasitoids to find endophytic pupa is important because they usually remain hidden which reduces emission of detectable volatiles (Bruinsma et al., 2009). Caterpillars may build shelters as protection that reduce its parasitism (Rodovalho et al., 2007).

Females of the parasitoid Brachymeria intermedia (Nees, 1834) (Hymenoptera: Chalcididae) can identify kairomones of Lymantria dispar (Linnaeus, 1758) (Lepidoptera: Lymantriidae) after being exposed to pupa of this host (Cardé and Lee, 1989). This indicates that searching-behaviors may depend on acquired experience of parasitoids (Hoballah and Turlings, 2005; Peñaflor et al., 2011). Contact with host before releasing may improve searching efficiency of laboratory reared parasitoids released in the field (González et al., 2011). Trichospilus diatraeae Cherian and Margabandhu, 1942 (Hymenoptera: Eulophidae) parasitizes insect pupa, mainly those of lepidopterans, and present potentially for biological control of agricultural and forest pests (Boucek, 1976; Zaché et al., 2010; Melo et al., 2011). The ability of this insect to find and parasitize D. saccharalis pupae inside sugarcane stalksare related with semiochemicals (Krugner et al., 2008), vibrations (Fischer et al., 2003), and/or chromatic and achromatic cues (Fischer et al., 2004).

Diatraea saccharalis is an important pest of sugarcane, because the intensity of the attack and cause losses in sugar and alcohol productivity (Segato et al., 2006; Dinardo-Miranda et al., 2012). Controlling the sugarcane borer with chemicals is difficult, because this insect develops in a protected location, inside the stem of the plant (Vacari et al., 2012). Therefore, biological control with parasitoids has been the most used way to combat this insect, so it is important to simulate the natural conditions before performing releases of T. diatraeae in the plantations of sugarcane, to check efficiency of parasitism in the field.

The present work evaluated capacity of T. diatraeae to search and parasitize D. saccharalis pupae in the presence of final instar caterpillars or fecal matter of this host.

Rearing D. saccharalis

Diatraea saccharalis pupae were supplied by Empresa Agentes Biológicos BUG. This insect was reared with the following methodology: recently hatched caterpillars were maintained in glass tubes (8.5 x 2.5 cm) sealed with cotton and fed an artificial diet until pupa stage. Pupae were collected, sexed, and 20 males and 30 females were placed together for ovipositon in PVC cages (22 x 10 cm) lined with sheets of sulfite paper humidified with distilled water. This PVC cages were sealed with a voile-type fabric and elastic (Parra, 2007).

Rearing T. diatraeae

Trichospilus diatraeae adults were maintained in glass tubes (14 x 2.2 cm) sealed with cotton and fed with drops of pure honey. D. saccharalis pupae with 24 to 48 hours old were subsequently introduced into these tubes during 24 hours. Pupae were removed and individualized in glass tubes (14 x 2.2 cm) in a chamber with controlled conditions chamber (25 ± 2 °C, 70 ± 10 % relative humidity, under a 14:10 light/ dark) until emergence (Pereira et al., 2008).

Experimental Design

Sugarcane stalks were cut in 20 cm long segments. An orifice was made in each segment and a 24 hour-old D. saccharalis pupa (184.00 ± 0.01 mg) was placed in each cavity. After the fixed inside each cavity and the stalk segments placed individually in transparent plastic tubes (25 x 9 cm) with 21 T. diatraeae females for 72 hours (Chichera et al., 2012). Pupae were then removed and individualized in glass tubes (14 x 2.2 cm) in a chamber with controlled conditions (25 ± 2 °C, 70 ± 10 % relative humidity, 14:10 light/dark) to evaluate parasitism and to observe the emergence of T. diatraeae. Controls consisted of D. saccharalis pupae fixed into sugarcane stalk segments under identical conditions, but without T. diatraeae females. Treatments consisted of exposing the parasitoid to: a pupa (T1); a pupa and a caterpillar (T2) or a pupa and the fecal matter (T3) of D. saccharalis. Treatment T2 had two holes in the stalks (one at each internode) with one pupa in one hole and a fourth or fifth instar caterpillar in the other one. Treatment T3 had one pupa in an orifice into the stalk with fecal matter of D. saccharalis around its external area.

Each parcel was exposed to 21 T. diatraeae females, with 12 replications in an entirely randomized design. It was evaluated the percentage of parasitism [;(number of pupae of D. saccharalis with emergence of parasitoid + pupae without adult emergence of D. saccharalis) / (total number of pupae) x 100; the emergence percentage [;(number of pupae of D. saccharalis to adult emergence of parasitoids) / (number of parasitized pupae) x 100 and progeny per pupa (number of parasitoid emerged per pupa of D. saccharalis). The successful of search of the parasitoid was measured by the percentage of parasitism of pupae. Percentages of T. diatraeae parasitism were analyzed with a general linear model with binomial distribution (p ≤ 0.05) using the R Statistical System software package (Ihaka and Gentleman, 1996). This analysis was performed using the original non-parametric data in percentages to facilitate interpretation. Data of emergence of T. diatraeae progeny were submitted to an analysis of variance with the test F at 5 % significance.

RESULTS

The present of final instar caterpillars or fecal matter of D. saccharalis affected the search and percentage of parasitism of females T. diatraeae. Percentage of D. saccharalis pupa parasitized by T. diatraeae was 50.00 %, 83.33 % and 16.66 % in the T1, T2 and T3, respectively (X²= 3.896, p = 0.04) (Fig. 1). ]]>

The presence of D. saccharalis caterpillars increased its shearching and parasitism of T. diatraeae.

Emergence of T. diatraeae adults from D. saccharalis pupa was similar between treatments with pupa (66.00 %) or pupa and caterpillars (70.00 %) (p > 0.05). This parasitoid did not emerged in the treatment with pupa and fecal matter of D. saccharalis.

Progeny of T. diatraeae from D. saccharalis pupae was similar between treatments with pupae and caterpillars or only pupae (Table 1) of this host.

DISCUSSION

The ability of T. diatraeae to find D. saccharalis pupae in the orifices in sugarcanes talks this species is important for biological control (Chichera et al., 2012). High parasitism levels of D. saccharalis pupae indicated potential of T. diatraeae as a biological control agent of this lepidopteran.

The parasitism of T. diatraeae in pupae of D. saccharalis introduced in the stalks of sugarcane was 50 %. Chichera et al. (2012) also noted 56 % parasitism in the experiment where the pupae of D. saccharalis were introduced in stems and exposed to T. diatraeae. A total of 83.33 % of D. saccharalis pupae was parasitized in the presence of caterpillars that host, this indicates that T. diatraeae was stimulated in the presence of larvae.

Higher ability of T. diatraeae to search D. saccharalis pupae with host caterpillars present suggests that it can recognize substances released by them and that they were close to pupation. As Cotesia kariyai (Watanabe, 1937) (Hymenoptera: Braconidae) females can distinguish chemical from damage by Pseudaletia separata (Walker, 1865) (Lepidoptera: in sugarcane stalks. Treatments: pupa, pupa and a caterpillar or pupa and fecal matter 25 ± 2 ° C, RH: 70 ± 10 % and 14 hours. Treatments Progeny Pupa 188.00 ± 55.50 a Pupa and caterpillar 231.57 ± 45.64 a Pupa fecal matter - Means followed by same letter do not differ by the F test (p > 0.05). (-) No progeny was obtained. Noctuidae) caterpillars up to fourth instar, but not between later ones (Takabayashi et al., 1995) - when they are not appropriate for parasitism.

Lower parasitism of D. saccharalis pupae by T. diatraeae with host fecal matter may be due to odors released these residues. Additionally, this fecal matter used in the experiment came from D. saccharalis caterpillars reared on artificial diet, and may have different composition in fecal matter of caterpillars fed on sugarcane plants in the natural environment. The searching behavior of the parasitoid Cotesia flavipes (Cameron, 1891) (Hymenoptera: Braconidae) is mediated by a water-soluble substance from the fecal matter of D. saccharalis caterpillars. The contact with this substance induces searching-behavior characterized by reduced locomotion and tapping the feces with its antenna (Van Leerdam et al., 1985). On the other hand, semiochemicals may not be important for Spathius agrili Yang, 2005 (Hymenoptera: Braconidae) to f ind Agrilus planipennis Fairmaire, 1888 (Coleoptera: Buprestidae) by this parasitoid females rely on host-generated vibrations to find suitable hosts (Wang et al., 2010).

Pupae and caterpillars of D. saccharalis together in sugarcane stalks favored parasitism of this pest by T. diatraeae by simulating naturally infested plants. Volatile compounds released from the sugarcane stalks due to D. saccharalis caterpillar-feeding may facilitated searching of pupae of this host by this natural enemy. Cabbage plants infested by Plutella xylostella (Linnaeus, 1758) (Lepidoptera: Plutellidae) (Girling et al., 2011) stimulated searching behavior of females of the larval parasitoid Cotesia vestalis (Haliday, 1834) (Hymenoptera: Braconidae). The parasitoid Trichogramma pretiosum Riley, 1879 (Hymenoptera: Trichogrammatidae) was attracted by volatile compounds released by corn plants damaged by caterpillars of Elasmopalpus lignosellus (Zeller, 1848) (Lepidoptera: Pyralidae) (Xavier et al., 2011).

The presence of D. saccharalis caterpillars in sugarcane stalks increased its searching and parasitism by T. diatraeae - which could be due to the perception and identification of substances released by the caterpillars or to odors from damaged sugarcane stalks. On the other hand, fecal matter from D. saccharalis reduced parasitism, which could be attributed to chemicals such us not identified by T. diatraeae. The origin and compositions of chemical substances that help this parasitoid to search host pupae need to be investigated to understand the efficiency of T. diatraeae to control D. saccharalis in the field.

In summary, T. diatraeae females searched and parasitized D. saccharalis pupae in sugarcane stalks in the laboratory. The presence of D. saccharalis caterpillars favored searching and increased parasitism of pupae of this pest in sugarcane stalks. Fecal matter from D. saccharalis caterpillars reduced parasitism by T. diatraeae.

ACKNOWLEDGMENTS

To Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for financial support.

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