New records of natural enemies of Plutella xylostella (L.) (Lepidoptera: Plutellidae) in Pernambuco, Brazil

SCIENTIFIC NOTE

Depto de Agronomia-Entomologia, Univ Federal Rural de Pernambuco, Av Dom Manoel de Medeiros s/n, Dois Irmãos, 52171-900, Recife, PE, Brasil; [e-mail]

ABSTRACT

We report the occurrence of natural enemies of Plutella xylostela (L.) in organically farmed kale in Pernambuco, Brazil. Seven natural enemies were observed parasitizing or preying on larvae and pupae of P. xylostella - three parasitoids: Cotesia plutellae Kurdjumov (Hym.: Braconidae), Conura pseudofulvovariegata (Becker) (Hym.: Chalcididae) and Tetrastichus howardi (Olliff) (Hym.: Eulophidae), and four predators: Cheiracanthium inclusum (Hentz) (Araneae: Miturgidae), Pheidole sp.Westwood (Hym.: Formicidae), nymphs and adults of Podisus nigrispinus (Dallas) (Hem.: Pentatomidae), and one unidentified species of solitary wasp. Beyond recording these natural enemies, data on predation of P. xylostella larvae in the field and laboratory by C. inclusum are presented.

Key words: Natural biological control, Cotesia, Conura, Tetrastichus, Cheiracanthium, Podisus, Pheidole

The diamondback moth (DBM), Plutella xylostella (L.), is the most destructive pest of crucifers worldwide. The estimated average control cost for DBM is greater than one billion dollars per year (Talekar 1992, Haseeb et al 2004). Intensive insecticide use continues to be the primary method of control against P. xylostella (Barros et al 1993, França & Medeiros 1998, Cheng et al 2008). As a result of biological and behavioral traits of DBM (e.g., great ability to disperse, high fecundity and short life cycle) and conditions offered by the environmental sites (e.g., availability of various crucifers in neighbor fields and throughout the year), P. xylostella has been considered as difficult to control. Thus, use of biological control methods is important for the management of this pest, and augmentation of biological control agents already present is prominent because it has minimum or no cost to growers.

In this work we report natural enemies of P. xylostella on an organic farm of kale crop (~90 days old) located in Chã Grande, Pernambuco State, Brazil (08º15'14.4''S and 35º30'0.3''W with an altitude of 505 m). To sample the natural enemies we exposed sentinel 3^rd-instar DBM larvae at the rate of 30 larvae per kale plant in the field. The exposure system consisted of 15 plants distributed along two transects marked in the study area. Selected plants were eight meters apart and distributed throughout the kale field. Eight out of 15 plants monitored were confined using cylindrical cages (50 cm diameter x 80 cm high) made with 4 mm mesh nylon fastened with wood sticks. Three days after infestation, all remaining DBM larvae were collected, and held for rearing until either an adult DBM or a parasitoid emerged. Predators observed directly preying on larvae or pupae in the field were noted.

Because there were significantly fewer P. xylostella larvae recovered in the uncaged plants, and the caged plants excluded spiders and predatory wasps, a study was conducted in the field and in the laboratory to measure the predation rates of the spider species on DBM larvae. The spider species found preying upon DBM larvae in the field was identified as Cheiracanthium inclusum (Hentz) (Araneae: Miturgidae).

In the laboratory, potted cabbage plants at 5-7 leaves developmental stage were infested with 3^rd-4^th instar DBM larvae at rate of 10 larvae per plant. To cage the spider on the plants, we used 2 L plastic bottles, inverted over the plants. A single female C. inclusum spider was released into the cage 1h after the DBM larvae infestation and 20 replicates established. Spiders used in the experiments were unfed for 48h to equalize the hunger level. After 48h the number of DBM larvae alive per cage was recorded. To measure natural mortality 20 caged plants containing only DBM larvae were established.

The predation of DBM larvae by spiders was also studied in the field using 22 kale plants caged with organdy (60 x 40 cm) tied to the base of the plants. The cages had a 25cm-long lateral zipper allowing access to the inside. Ten DBM larvae per plant were carefully released over the leaves; following that, one female spider was released in each of 17 cages. The five remaining cages served as controls to measure natural mortality in the absence of the spiders. After 72h, each caged plant was fully inspected and the number of live DBM larvae-pupae was recorded.

The overall average (± SE) numbers of recovered larvae (Fig 1) from uncaged and caged plants were 3.0 ± 0.58 and 9.4 ± 0.67, respectively, and was significantly higher on caged plants [F_{df = 1, 151} = 63.96, P < 0.0001; repeated measures analysis of variance using SAS package (SAS Institute 2001)]. The loss by natural mortality across the study period was up to 89.9 ± 1.95% and 6.6 ± 2.25% on uncaged and caged plants, respectively. On the other hand, there was no significant effect of the interaction between treatments (caged and uncaged plants) and survey dates (P = 0.4287).

Seven species of natural enemies were collected including three parasitoid wasps and four predator species (Fig 2). The parasitoids emerging from recovered P. xylostella were: Cotesia plutellae Kurdjumov (Hym.: Braconidae), Conura pseudofulvovariegata (Becker) (Hym.: Chalcididae) and Tetrastichus howardi (Olliff) (Hym.: Eulophidae). The predators observed directly attacking DBM larvae and pupae were: the spider C. inclusum, nymphs and adults of the predator Podisus nigrispinus (Dallas) (Hem.: Pentatomidae), ants of the genus Pheidole sp. (Hym.: Formicidae), and one unidentified solitary wasp species (Hymenoptera). This unidentified wasp built a mud nest inside the vial (1 x 7.5 cm) used for Oomyzus sokolowkii (Kurdjumov) (Hym.: Eulophidae) being released in this field. Two vials held one mud cell each and contained 10 and 14 DBM pre-pupae larvae, respectively. In each cell containing DBM larvae there was one egg deposited by the solitary wasp. Although the egg hatched it failed to reach the pupal stage in the laboratory; therefore, we did not obtain adults to submit for species identification but based on the nesting habit it seemed to be a sphecid wasp.

Among the parasitoids found in this study, C. pseudofulvovariegata and C. plutellae were previously found in Brasília, DF by Guilloux et al (2003) and Monnerat et al (2000), respectively. Therefore, this is only the second time they are reported in Brazil parasitizing DBM. Meanwhile, this is the first report of T. howardi.

Among the predators found, P. nigrispinus is known to feed on P. xylostella in the laboratory; however this is the first report of field observation of P. nigrispinus preying on DBM larvae. In addition, ants of the genus Pheidole sp. have also been reported as predator of DBM in India, contributing with 58.8% of DBM larvae losses in a cauliflower field (Agarwal et al 2007).

When C. inclusum spiders were offered DBM larvae on caged plants; they consumed an average of 4.8 ± 0.88 and 5.9 ± 0.53 larvae under laboratory and field conditions during 48h and 72h, respectively. In both cases, there was no mortality of DBM larvae in the cages lacking spiders; therefore we can infer that larval mortality was caused by spiders' predation since no other natural enemies had access inside the cages.

Acknowledgments

We thank Marcelo Tavares (UFES), John La Salle (CSIRO), Alexandre Bonaldo (UFPA), Dominique Bordat (CIRAD) and Rodrigo M Feitosa (USP) for the identification of Conura pseudofulvovariegata, Tetrastichus howardi, Cheiracanthium inclusum, Cotesia plutellae and Pheidole sp., respectively. To Júlio Correia Alves and Miguel Raimundo de Aguiar Filho for providing the study area and the production of plants in the field, and Antônio Carlos Florêncio de Souza (SFA-MAPA, Recife, PE) for helping with the photos, and Robert W Matthews (UGA) for significant suggestions in the manuscript. This work was partially funded by CAPES Foundation project PROCAD No. 83054.

Received 15/IV/09.

Accepted 15/VII/09.

Edited by Roberto A Zucchi - ESALQ/USP

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New records of natural enemies of Plutella xylostella (L.) (Lepidoptera: Plutellidae) in Pernambuco, Brazil

Christian S A Silva-Torres; Itillio V A F Pontes; Jorge B Torres; Reginaldo Barros

Publication Dates

• Publication in this collection
  19 Nov 2010
• Date of issue
  Oct 2010

History

• Received
  15 Apr 2009
• Accepted
  15 July 2009