Research optimizes biological control of pests that affect soybean crops

Article published in the magazine Insects accurately determines the dispersal distance of a type of wasp that neutralizes a common pest in soybean production areas – the euschistus heros, an insect known as the brown stink bug. This is a serious challenge to soybean production in South America and its control is difficult due to resistance to chemical insecticides, say the authors of the article. The solution, the telenomus podisi, is a species of parasitoid microwasp, described by the North American entomologist William Harris Ashmead in 1893.

With the study conducted by scientists from Universidade Estadual Paulista (Unesp) and Oklahoma State University (United States), it is possible to improve the release of the wasp to ensure biological control of the stink bug, which also affects cotton and sunflower growing areas, in addition to pastures.

Scientific research has received various support from Fapesp (projects 18/02317-5, 19/10736-0 and 18/19782-2).

The females of T. podisi locate eggs E. heroes on plants and lay their own eggs there, interrupting the development of the brown stink bug at the beginning of the development cycle.

“The pest eggs become dark in color and give rise to new wasps instead of new bed bugs. Subsequently, these wasps will parasitize more pest eggs”, details Regiane Cristina de Oliveira, professor in the Department of Plant Protection at the Faculty of Agricultural Sciences (FCA) at Unesp, Botucatu campus. To offer producers the correct way to use the natural agricultural pesticide, several studies were carried out to understand how it should be released – the number of wasps and the best distance between the release points, among other aspects.

The group of researchers verified under field conditions that the dispersion capacity of T. podisi, influenced by the soybean growth stage, it varied between 31 and 39 meters. The maximum parasitism rate of bed bug eggs was about 60%. Based on these results, the authors recommend that wasp release points be spaced no more than 30 meters apart to provide effective control of the pest, one of the most aggressive in soybean crops. O E. heroes causes damage to the pods (can cause loss of up to 30% of productive potential). In autumn, the insect pest begins looking for shelter under the straw, where it remains until summer. During this time, it accumulates lipids and does not feed, remaining in a state of quiescence (physiological state of low metabolic activity).

As the effectiveness of the parasitoid depends on the ability to find hosts, knowledge of its dispersal capacity makes it possible to adjust the logistics and release technique. “This optimizes the management of bedbugs through biological control programs applied in extensive areas of monoculture,” says Oliveira, who is an agronomist with a degree from the Federal University of Espírito Santo, a master’s degree in agricultural entomology from Unesp and a PhD in entomology from the Escola Superior de Agricultura Luiz de Queiroz from the University of São Paulo (Esalq-USP), with a postdoctoral degree at Mississippi State University (United States).

In addition to Oliveira, the article is written by William Wyatt Hoback and Rafael Hayashida, from the Department of Entomology and Plant Pathology at the University of Oklahoma, and Gabryele Ramos, Daniel Mariano Santos and Daniel de Lima Alvarez, from FCA-Unesp.

The article received the following summary (free translation):

"An augmentative biological control program using egg parasitoid Telenomus podisi Ashmead (Hymenoptera: Platygastridae) is a promising tool for managing the brown stink bug, euschistus heros (Fabricius) (Hemiptera: Pentatomidae) in soybeans. You T. podisi are released as adults or pupae in eggs of E. heroes created in the laboratory. Due to the parasitoid's small size and potentially limited dispersal ability, determining the optimal release pattern is critical for biological control of the target pest. This study used sentinel eggs from E. heroes to investigate the dispersion of T. podisi in soybean crops during two distinct phenological stages: the beginning of flowering (Vn – R1) and the grain filling phase (R5 – R6). Data were analyzed using semivariograms and kriging maps. The results indicate significant differences in parasitism rates between the two stages of plant growth and between different matrices. The maximum dispersion range for T. podisi was calculated at 39 m in stage Vn-R1 with a maximum parasitism rate of 42%, while in stage R5-R6, the maximum dispersal range was calculated at 30,9 m with a maximum parasitism of 73%. Therefore, it is recommended that the release points of T. podisi are not spaced more than 30 m apart. These results provide valuable information for future research and applications in biological control strategies, including adjusting logistics and release technique depending on the phenological stage of the crop."

The full text can be read at doi.org/10.3390/insects15030192