DRYINIDAE (HYMENOPTERA: CHRYSIDOIDEA) PARASITOIDS OF THE CORN LEAFHOPPER, Dalbulus maidis (DELONG & WOLCOTT) (HEMIPTERA: CICADELLIDAE), IN ARGENTINA, WITH DESCRIPTION OF THE MALE OF Gonatopus moyaraygozai OLMI

Eduardo G. Virla and Massimo Olmi

Eduardo G. Virla. Doctor in Biology (Zoology), Universidad Nacional de La Plata, Argentina. Researcher CONICET. Address: PROIMI-Biotechnology. Av. Belgrano & Pje. Caseros (T4001 MVB) San Miguel de Tucumán, Tucumán, Argentina. e-mail: evirla@proimi.org.ar

Massimo Olmi. Doctor in Agricultural Sciences, Turin University, Italy. Professor, Università degli studi della Tuscia, Viterbo, Italy. e-mail: olmi@unitus.it

SUMMARY

The parasitoids of the Corn Leafhopper, Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Auchenorrhyncha) were studied in Tucumán Province, Argentina. Leafhoppers parasitized by Dryinidae (Hymenoptera: Chrysidoidea) were collected in cornfields from Dec 2003 to Apr 2005. Dryinid adults belonging to three species, Gonatopus caraibicus (Olmi), Gonatopus contortus Olmi, and G. moyaraygozai Olmi, were obtained. G. moyaraygozai is quoted for the first time in Argentina, and the male is described for the first time. This contribution presents the first field host-association record for G. caraibicus and D. maidis; in addition, G. contortus, and G. moyaraygozai are cited for the first time attacking Corn Leafhopper populations. Data on the parasitization rate by G. moyaraygozai are given.

DRYINIDAE (HYMENOPTERA: CHRYSIDOIDEA) PARASITOIDES DE LA CHICHARRITA DEL MAÍZ, Dalbulus maidis (DELONG & WOLCOTT) (HEMIPTERA: CICADELLIDAE), EN ARGENTINA, Y DESCRIPCIÓN DEL MACHO DE Gonatopus moyaraygozai OLMI

RESUMEN

Se estudiaron los parasitoides de la chicharrita del maíz, Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Auchenorrhyncha) en la provincia de Tucumán, Argentina. Las chicharritas atacadas por Dryinidae (Hymenoptera: Chrysidoidea) fueron colectadas en campos de maíz entre dic 2003 y abr 2005. Se obtuvieron driínidos de tres especies diferentes: Gonatopus caraibicus (Olmi), Gonatopus contortus Olmi, y G. moyaraygozai Olmi. Se cita por primera vez a G. moyaraygozai en Argentina, y se describe al macho de dicha especie. Se registra por primera vez en campo la asociación parasitoide-hospedador de G. caraibicus y D. maidis; además, se mencionan por primera vez a G. contortus y G. moyaraygozai como parasitoides de la chicharrita del maíz. Se calculó la tasa de parasitoidización de G. moyaraygozai en campo.

DRYINIDAE (HYMENOPTERA: CHRYSIDOIDEA) PARASITOIDES DA CIGARRINHA DO MILHO, Dalbulus maidis (DELONG & WOLCOTT) (HEMIPTERA: CICADELLIDAE), EM ARGENTINA, E DESCRIÇÃO DO MACHO DE Gonatopus moyaraygozai OLMI

Resumo

Os parasitoides da cigarrinha do milho, Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Auchenorrhyncha) foram estudados na província de Tucumán, Argentina. As cigarrinhas atacadas por Dryinidae (Hymenoptera: Chrysidoidea) foram colectadas em cultivos de milho entre dezembro de 2003 e abril de 2005. Foram obtidos dryínidos de três espécies diferentes: Gonatopus caraibicus (Olmi), Gonatopus contortus Olmi e Gonatopus moyaraygozai Olmi. G. caraibicus, anteriormente obtido de D. maidis sómente em laboratório, foi criado também em campo. Pela primeira vez G. contortus e G. moyaraygozai são citados como parasitoides de D. maidis. De G. moyaraygozai, citado pela primeira vez em Argentina, foram obtidos ambos os sexos; a descrição do macho, anteriormente desconhecido, é feita pela primeira vez. A taxa de parasitismo de G. moyaraygozai foi avaliada em campo.

KEYWORDS / Argentina / Corn / Corn Leafhopper / Dryinidae / Parasitoids / Vector /

Received: 02/05/2007. Modified:10/05/2007. Accepted:10/08/2007.

Introduction

The Corn Leafhopper, Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Auchenorrhyncha) is the most common leafhopper feeding on corn in northern Argentina (Paradell et al., 2001). It causes great losses to corn crops in most parts of the tropical and subtropical Americas because it is able to transmit the following pathogens (Nault and Ammar, 1989): Corn stunt spiroplasm (CSS), Maize bushy stunt phytoplasm (MBSP) and Maize rayado fino virus (MRFV). The diseases caused by these pathogens seriously affect corn crops in Argentina (Giménez Pecci et al., 2002; Virla et al., 2004).

Dryinid wasps (Hymenoptera: Dryinidae) are highly specialized parasitoids of Hemiptera Auchenorrhyncha (treehoppers, leafhoppers, and planthoppers) nymphs and adults (Guglielmino and Olmi, 1997, 2006). Representatives of the family have been successfully utilized in several instances for the biological control of crop pests (Swezey, 1928; Olmi, 2000).

The Dryinidae species known in the Americas as parasitoids of D. maidis are Gonatopus bartletti Olmi 1984, Gonatopus caraibicus (Olmi, 1986) and Gonatopus desantisi Olmi and Virla 1993 (for references see Guglielmino and Olmi, 1997). Gonatopus bicolor (Haliday), quoted by Maes and Godoy (1993), cannot be a parasitoid of D. maidis because it is a European species not present in other continents and attacking only Delphacidae (Olmi, 1999). Agonatopus sp., quoted by Quezada (1979), is a mysterious species that has never been identified, but probably corresponds to Gonatopus bartletti Olmi.

Thirty five species of the genus Gonatopus Ljungh occur in Argentina (Virla and Olmi, 1998, 2007) and only two of them, G. caraibicus and G. desantisi, were mentioned as affecting D. maidis populations. The development of a research project on the natural enemies of Corn Leafhopper in northern Argentina resulted in the discovery of new parasitoids of D. maidis and permitted to obtain the new biological data reported below.

Material and Methods

Nymphs and adults of D. maidis were sampled by sweeping with a standard entomological net. Samples were collected in both subsistence and commercial cornfields in Tucumán province from Dec 2003 to Apr 2005.

Several individuals of the Corn Leafhopper parasitized by Dryinidae were obtained, as evidenced by the possession of the typical larval sac. Most of the specimens died as prepupa or pupa in laboratory, probably due to experimental environmental conditions (temperature and humidity). However, some Dryinid adults emerged, allowing the specific identification.

In order to estimate the rate of parasitism affecting the Corn Leafhopper population inhabiting a cornfield in Horco Molle, Tucumán, Argentina, site (26°47’29.3’’S and 65°19’39.7’’W; 636masl), a trial of three replicates of 10 sweep beating over the corn plants was done on Jan 28^th, 2004. All collected individuals were isolated in glass tubes containing corn leaves. Leaves were changed as needed, and leafhoppers were checked daily, looking for parasitization evidences. After 12 days, individuals without parasitization symptoms were considered as healthy.

Dried voucher, host as well as parasitoid specimens studied were deposited in the collection of Fundación e Instituto Miguel Lillo in San Miguel de Tucumán, Argentina.

Results

The following three species of Dryinidae parasitizing D. maidis were obtained: Gonatopus caraibicus (Olmi 1986), G. contortus Olmi 1984, and G. moyaraygozai Olmi 1991.

Gonatopus caraibicus Olmi

Reared specimens: One female specimen of G. caraibicus was obtained from a female adult of D. maidis on 14/VI/2004 in San Miguel de Tucumán (26°48’35.8’’S, 65°14’24.8’’W; 464masl).

Remarks: G. caraibicus is a broadly distributed species cited in Puerto Rico and Argentina (Olmi, 1984; Virla and Olmi, 1998; Virla, 2000). This species is known to parasitize the following leafhoppers (Cicadellidae): Exitianus obscurinervis Stål (De Santis et al., 1988); Amplicephalus simpliciusculus Linnavuori, Haldorus sexpunctatus Berg (Virla, 1992); Chlorotettix sp. (Virla and Olmi, 1998); Planicephalus flavicosta (Stål), Amplicephalus (Mendozellus) dubius (Linnavuori) and Graminella stelliger viridescens Linnavuori (Virla, 2000). Virla (1992) verified that G. caraibicus parasitized D. maidis in the laboratory, but the dryinid was not able to complete the development. Thus, this is the first field record confirming this host-species relationship.

Gonatopus contortus Olmi

Reared specimens: Female specimens of G. contortus Olmi were obtained from adults of D. maidis on 19/XII/2003 (1 ) and 23/II/2004 (2 ) in Ranchillos, Tucumán, Argentina (26°57’37.7’’S, 65°03’03.1’’W; 387masl). With these specimens, a small laboratory colony was established. The reproduction of this species was parthenogenetically telitokous.

Remarks: This species is known from Puerto Rico, Bolivia, Paraguay, and Argentina (Olmi, 1984; Virla and Olmi, 1998; Olmi et al., 2000; Garcete Barrett, 2001). It was previously mentioned as a parasitoid of Cicadellidae Deltocephalinae (Virla, 2001).

Gonatopus moyaraygozai Olmi 1991

Reared specimens: Two females and a male of G. moyaraygozai Olmi were obtained from parasitized corn leafhoppers collected on 28/I/2004 in Horco Molle, Tucumán, Argentina site. Later, two females were further bred from the same place on 13/II and 24/II/2004.

Remarks: This species was known only from México (Olmi, 1990) and it is now mentioned for the first time in Argentina. Cicadellidae was the previously known host of this parasitoid (Guglielmino and Olmi, 1997) and in México it was found attacking Dalbulus quinquenotatus De Long and Nault (Olmi, 1990), so that this is the first quotation of this species affecting D. maidis populations.

Only female specimens of G. moyaraygozai were known. The male reared during this study is the first known male of this species. It may be described as follows:

MALE: fully winged; length 1.62mm. Head brown, with mandibles testaceous; antennae brown; mesosoma black; gaster brown; legs brown. Antennae filiform; antennal segment 3 approximately twice as long as broad (6.3); antennal segments in the following proportions: 5:5:6:6:6:6:5.5:5.5:5:8. Head shiny, smooth, without sculpture; frontal line absent; occipital carina absent; POL= 5; OL= 1; OOL= 2.5; greatest diameter of posterior ocelli= 2. Scutum, scutellum and metanotum shiny, finely punctate, without sculpture among the punctures. Notauli complete, posteriorly separated; minimum distance between notauli much shorter than greatest diameter of posterior ocelli (1:2). Propodeum dull, completely reticulate rugose. Forewing hyaline, without dark transverse bands; marginal cell open; stigmal vein regularly curved. Dorsal process of the parameres (Figure 1) short, with proximal part slender and distal apex broadened. Palpal formula 5/2. Tibial spurs 1, 1, 2.

Parasitization rate

At a cornfield in Horco Molle site (Jan 28^th, 2004), a total of 217 corn leafhoppers were captured (68 nymphs, 101 females and 48 males). Mean of D. maidis individuals/10 sweep beating was 72.3 (SD= 9.3). Eleven individuals were parasitized by dryinid wasps (6 nymphs, 4 females and only one male), but only 3 adults of G. moyaraygozai Olmi emerged (2 females and 1 male). So, the parasitization rate measured on that day was 5.1%.

Acknowledgements

The research described in the present paper was partially supported by FONCYT-PICT project Nº 08-15029, and by the bilateral cooperation grant IT-PA05-AYE/XV/040.

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