Trichogramma pretiosum in field release and under different temperatures in laboratory

Rosana Matos De Morais,Ricardo Bemfica Steffen,Tamires Silveira Moro,Gerusa Pauli Kist Steffen,Cleber Witt Saldanha,Joseila Maldaner,Evandro Luiz Missio

doi:10.1590/1808-1657001152018

Abstract

ABSTRACT This study aimed to evaluate a strain of Trichogramma pretiosum native to the central region of the state Rio Grande do Sul, Brazil, under different temperatures in laboratory and the parasitism of Helicoverpa zea after releases in corn field. Trichogramma pretiosum females were kept at 18, 25 and 30 °C and had their parasitism potential evaluated. Nine plots (400 m2) of maize were installed in randomized blocks under the treatments: 1) staggered release of parasitoids in three different occasions, at three-day intervals; 2) a single release of parasitoids; 3) no release of parasitoids. Ears were collected every four days and the number of caterpillars and eggs of H. zea in the maize silk and the number of damaged ears were estimated. Evaluation started after the tassels growth and ended with the drying of the styles-stigmas. To estimate the grain mass and the ear number and mass, two lines in each plot were delimited and reserved at the end of the cultivation cycle. In laboratory, the highest parasitism rate occurred at 25 °C (35.54%) and the lowest longevity at 30 °C (6.8 days). A total of 1,063 H. zea eggs were collected in the field, 69.52% were parasitized. The mean parasitism rate was higher in T1 (staggered release, 82.77%) than in control (51.87%), but there was no difference in grain yield. Based on the parasitism capacity of the studied strain, it can be potentially used in programs of biological control of H. zea in corn crops of Rio Grande do Sul.

Highlights

MATERIAL AND METHODSParasitoids of the genus Trichogramma Westwood (Hymenoptera: Trichogrammatidae) are an important group of natural enemies and comprise the most numerous genus within the Trichogrammatidae family
This study aimed to evaluate a strain of Trichogramma pretiosum native to the central region of the state Rio Grande do Sul, Brazil, under different temperatures in laboratory and the parasitism of Helicoverpa zea after releases in corn field
This study aims to evaluate the reproductive capacity of a Trichogramma pretiosum strain from the Central region of Rurais – Santa Maria (RS) (Brazil) under different temperatures in laboratory conditions

Summary

Introduction

MATERIAL AND METHODSParasitoids of the genus Trichogramma Westwood (Hymenoptera: Trichogrammatidae) are an important group of natural enemies and comprise the most numerous genus within the Trichogrammatidae family. The natural parasitism of Helicoverpa zea (Boddie) eggs (earworm) (Lepidoptera: Noctuidae) by T. pretiosum in corn crops often reaches 50%, but can occasionally reach over 90% of eggs (SÁ; PARRA, 1994). According to FORESTI et al (2012), the parasitism rate can be increased with releases of the agent in the field. The use of commercial strains of T. pretiosum for caterpillar control is a widespread technique among farmers since, compared with chemical insecticides, it is an efficient and low-price method that aims to restrict pesticide use (PARRA, 2010; FIGUEIREDO et al, 2015). The lack of information regarding the field release of these strains often results in unsuccessful outcomes and the technique is frequently disbelieved. It is crucial to establish the most appropriate release interval depending on the locality and infestation degree (SÁ; PARRA, 1993)

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