Release of the egg parasitoid Telenomus podisi to manage the Neotropical Brown Stink Bug, Euschistus heros, in soybean production

Highlights

• Telenomus podisi pupae released either encapsulated or unprotected have similar efficacy.

• 18750 pupae of Telenomus podisi/hectare significantly increases stink bug egg parasitism.

• Telenomus podisi release should be done with first stink bugs adults in the field.

• Telenomus podisi release and insecticide spray have similar stink bug control.

Abstract

Eushistus heros is one of the major pests in soybean in South America. Not only has insecticides constantly failed on its control but also triggered different negative side effects related to the overuse of chemicals. Among the biocontrol agents that can be used in Augmentative Biological Control, Telenomus podisi stands out due to its high parasitism capacity on eggs of its hosts. Therefore, this study aimed to assess T. podisi release strategies and moments (release done together with the detection of first E. heros adults in the area as well as together with fungicide sprays), in order to reach optimal parasitoid field performance. For this purpose, a replicated experiment was conducted with a soybean crop located in Londrina, Paraná, Brazil, during 2017/18 and 2018/19 crop seasons. Treatments consisted of 18750 released T. podisi pupae (released either inside cardboard capsules or as unprotected pupae sprinkled in bulk, at different moments) and were evaluated against insecticide spraying strategies. At harvest, yield and quality of the seeds were measured. Overall, our results clearly indicate that T. podisi pupae can be released either encapsulated or unprotected, with similar efficacy. Their release in the field increased E. heros egg parasitism to 70% and 50%, in 2017/2018 and 2018/2019, respectively. Thus, T. podisi can be efficiently used to control stink bug eggs. However, since the number of stink bugs ≥0.5 cm in the field highly depends on its migration from neighboring fields, it is important to use T. podisi inside integrated pest management.

Introduction

Stink bugs are the most important pest group causing soybean (Glycine max) yield loss in South America (Bueno et al., 2015). They are piercing-sucking insects, feeding directly from soybean pods, seriously affecting crop yields by impairing the physiological and sanitary quality of the seeds (increased percentage of dead embryos, fungi contamination besides weight and size reduction of seeds and grains) (Corrêa-Ferreira and Azevedo, 2002). Of this group, the Neotropical Brown Stink Bug, Euschistus heros (Hemiptera: Pentatomidae) is the most important species due to its high frequency, abundance and management difficulties (Panizzi and Corrêa-Ferreira, 1997; Panizzi, 2013). Currently, soybean growers can only rely on chemical insecticides to control this pest. However, the overuse of insecticides has trigged rapid selection of resistant populations, reduction of biological control agents, and outbreaks of secondary pests, among other undesirable consequences (Sosa-Gómez et al., 2001; Sosa-Gómez and Silva, 2010). Therefore, a more sustainable stink bug management is of major theoretical and practical interest.

Among the most environment-friendly and sustainable pest management tools available, augmentative biological control stands out, a method that has been applied for over 100 years (Cock et al., 2010) on more than 30 million ha worldwide (van Lenteren et al., 2018). Egg parasitoids have wide use in augmentative biological control and can be considered the most important stink bug biocontrol agents (Koppel et al., 2009; Laumann et al., 2010). Among the different species of egg parasitoids that can be used in augmentative biological control of E. heros, Telenomus podisi (Hymenoptera: Platygastridae) is noteworthy due to its high parasitism and control efficacy against its hosts (Peres and Corrêa-Ferreira, 2004; Queiroz et al., 2018; Silva et al., 2018). Despite its huge potential to control stink bugs, large-scale field release of T. podisi is still limited due to the lack of information regarding release technologies such as how and when the parasitoids are best released (Pinto and Parra, 2002), especially when extensive crops such as soybean are concerned.

Ground release of parasitoid pupae was the first standard method in countries where parasitoid production and labor costs were low (Huffaker, 1977). Later, this method was replaced by aerial release of parasitoid pupae in larger areas (Bouse and Morrison, 1985). Egg parasitoid pupae can be either released inside capsules, which are usually made of cardboard or other organic material, or spread directly, without protection, over the field in bulk (Smith, 1994; Pinto and Parra, 2002; Pinto et al., 2003). Parasitoid field success highly depends on climatic conditions, the number of released parasitoids, time and frequency of releases, as well as the parasitoid distribution method (Hassan, 1994), which is virtually undeveloped for T. podisi release to control E. heros in soybean fields. Better understanding of these interacting parameters may help growers to choose the optimal T. podisi release strategy. Therefore, this study was carried out to evaluate different T. podisi release strategies at different moments, in order to reach the best T. podisi field performance.