Egg parasitoids of Anticarsia gemmatalis Hübner (Lepidoptera: Noctuidae) in soybeans

Parasitóides de ovos de Anticarsia gemmatalis Hübner (Lepidoptera: Noctuidae) na cultura da soja

Insecta; controle biológico; lagarta da soja; Tricho-gramma sp.; Telenomus sp.; Encarsia sp.

SCIENTIFIC NOTE

Egg parasitoids of Anticarsia gemmatalis Hübner (Lepidoptera: Noctuidae) in soybeans

Parasitóides de ovos de Anticarsia gemmatalis Hübner (Lepidoptera: Noctuidae) na cultura da soja

Luís A. Foerster; Marion R.F. Avanci

Dept° de Zoologia, UFPR, Caixa postal 19.020, 81531-990, Curitiba, PR

RESUMO

Levantamentos em lavouras de soja foram conduzidos durante cinco safras (1994/95 a 1998/99) em três localidades no Sul do Paraná, para verificar a ocorrência de parasitismo em ovos de Anticarsia gemmatalis Hübner (Lepidoptera: Noctuidae). Foram encontradas cinco espécies pertencentes a três famílias de Hymenoptera: Trichogramma pretiosum Riley, T. rojasi Nagaraja & Nagarkatti, T. atopovirilia Oatman & Platner (Trichogrammatidae), Telenomus cyamophylax Polaszek (Scelionidae) e Encarsia porteri (Mercet) (Aphelinidae). Destas, T. atopovirilia e E. porteri são citadas pela primeira vez parasitando ovos de A. gemmatalis na América do Sul. O elevado número de espécies encontrado demonstra que os parasitóides de ovos desempenham um papel relevante no controle natural da lagarta da soja; todavia, para o seu potencial ser efetivamente explorado, há necessidade do uso racional de inseticidas seletivos que permitam a sobrevivência desses parasitóides.

Palavras-chave: Insecta, controle biológico, lagarta da soja, Tricho-gramma sp., Telenomus sp., Encarsia sp.

Although the velvetbean caterpillar Anticarsia gemmatalis Hübner is the main defoliator of soybeans in Brazil (Panizzi et al. 1977, Ferreira & Panizzi 1978), studies regarding parasitism on this species have been largely restricted to the larval stage (Panizzi et al. 1977, Foerster & Guillén 1979), with few attempts to survey the occurrence of egg parasitoids. Hohmann et al. (1989) reported Trichogramma pretiosum Riley in eggs of A. gemmatalis and Zucchi & Monteiro (1997) surveyed the literature on Trichogramma in South America. Elsewhere in South America, T. pretiosum and Encarsia sp. were recorded in Argentina on eggs of A. gemmatalis (Frias et al. 1991-93).

Field surveys were carried out during four soybean seasons from 1994/95 to 1998/99 in southern Paraná State, Brazil in areas with a history of low insecticide use, to investigate the occurrence of parasitism in eggs of A. gemmatalis.

Four methods were used to survey A. gemmatalis eggs in the field; l. Random collection of eggs from the plants (40 to 60 eggs/week); 2. Placement of stiff index cards containing 40 eggs obtained in laboratory and tied to the plants; 3. Direct placement of laboratory-obtained eggs on soybean leaves (40 eggs/plant), and 4. Release of A. gemmatalis moths in nylon cages covering the whole plant, and collection of the eggs laid by the caged moths. Except for the collection of naturally laid eggs, the eggs were left in the field for a 3-5 day exposure period and then transferred to the laboratory to assess the incidence of parasitism.

The strips containing glued eggs of A. gemmatalis was the least effective method to detect parasitism, due to the high rate of predation on the exposed eggs; once the strip was found by a predator, all eggs of the batch were consumed. The other three methods were effective in detecting parasitism; the attachment of laboratory-obtained eggs directly to the leaf surface was the most time-consuming, while the collection of naturally laid eggs depended largely on the skill of the collector to detect the small-size eggs of A. gemmatalis on the soybean leaves. Thus, the least time-consuming method was the release of 10 pairs of moths inside a nylon cage containing four soybean plants and the further collection of the eggs 3-5 days after the release of the moths. In this method, the mesh size of the nylon did not preclude the access of adult parasitoids into the cage.

Five species of Hymenoptera belonging to three families were found parasitizing eggs of A. gemmatalis in the three areas surveyed (Table 1). Three species of Trichogramma were identified: T. pretiosum was the most common, being found in all four seasons and in all localities; T. rojasi Nagaraja & Nagarkatti was collected in Quatro Barras (1995/96) and Fazenda Rio Grande (1996/99), but not in Lapa, while T. atopovirilia Oatman & Platner was found in 1997/98 in Fazenda Rio Grande (Table 1). Neither T. rojasi nor T. atopovirilia had been previously found in eggs of A. gemmatalis. Nagaraja & Nagarkatti (1973) described T. rojasi collected in Chile, from eggs of Tatochila sp. (Lepidoptera: Pieridae) on Trifolium sp. and from Rachiplusia ou Guén. (Lepidoptera: Noctuidae) on alfalfa and beans. In Cuba, T. rojasi was found parasitizing eggs of Mocis latipes (Guén.) (Lepidoptera: Noctuidae) (Galán & Rodríguez 1991). In Brazil, T. rojasi is cited by Zucchi & Monteiro (1997) from the specimens collected in this survey in Southern Paraná and identified by Dr. John Pinto from the University of California, Riverside. In Brazil, T. atopovirilia was previously recorded from eggs of Helicoverpa zea (Boddie) and Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) collected on maize and from Erinnyis ello (L.) (Lepidoptera: Sphingidae) on cassava (Zucchi & Monteiro 1997). Although T. pretiosum is the prevalent species of Trichogramma in eggs of lepidopterous pests, in Brazil only Hohmann et al. (1989) have previously reported its incidence in eggs of A. gemmatalis. In Argentina, T. pretiosum was observed in eggs of A. gemmatalis by Frías et al. (1991-93).

In the 1994/95 soybean season, a new species of Telenomus (Hymenoptera: Scelionidae) was found parasitizing eggs of A. gemmatalis in Lapa; this species was described by Polaszek & Foerster (1997) as Telenomus cyamophylax Polaszek. In 1998/99, T. cyamophylax was also collected in Fazenda Rio Grande.

In 1997/98, the survey revealed in Fazenda Rio Grande a species of Aphelinidae not previously cited parasitizing eggs of A. gemmatalis in Brazil: Encarsia porteri (Mercet). Species of Encarsia may have different ontogenies between males and females; some are heterotrophic parasitoids, in which the females develop as primary parasitoids of whiteflies and the males develop in lepidopterous hosts (Stoner & Butler 1965, Gauld & Bolton 1988). In the present survey, only males of E. porteri emerged from eggs of A. gemmatalis. In Chile, E. porteri was found parasitizing eggs of Rachiplusia nu (Guenée) (Arretz et al. 1994) and H. zea (Guerrero et al. 1993), and in Argentina, Frías et al. (1991-93) reported Encarsia sp. in eggs of A. gemmatalis in soybeans.

The relative incidence among parasitoid species was not quantified in Lapa and Quatro Barras (1994 until 1997). In 1998/99, in Fazenda Rio Grande, the relative abundance of each parasitoid was assessed, and T. pretiosum accounted for over 90%, followed by T. atopovirilia (3.6%), T. rojasi (2.5%), T. cyamophylax (1,5%) and E. porteri (0.5%). Despite the strong predominance of T. pretiosum during this season, the other parasitoid species may be important under different climatic conditions or at different host densities.

The results show that eggs of A. gemmatalis are attacked by a complex of parasitoid species that may have a significant role in the control of the velvetbean caterpillar. However, the indiscriminate use of non-selective insecticides in areas under continuous insecticide pressure may be suppressing the action of these natural enemies. In all localities evaluated in this survey, insecticide use has been restricted; in two of the areas (Fazenda Rio Grande and Quatro Barras), soybean had been recently introduced, and in Lapa, although with a long history of soybean cropping, the study area had been under pest management during the past 12 years, thus with restricted and selective use of insecticides. The large variety of parasitoid species found in these circumstances clearly illustrates the importance of environmental quality on the abundance of beneficial species.

Acknowledgements

The authors are grateful to Dr. John D. Pinto, University of California, Riverside, Dr. Gregory Evans, University of Florida, Gainesville and Dr. Roberto A. Zucchi, University of São Paulo, Piracicaba for the identification of T. rojasi, E. porteri and T. atopovirilia, respectively. This research was conducted under CNPq grant number 521096/95.

Literature Cited

Received 06/VII/98. Accepted 21/VI/99.

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Publication Dates

• Publication in this collection
  11 May 2006
• Date of issue
  Sept 1999

History

• Accepted
  21 June 1999
• Received
  06 July 1998