TWN Info Service on Biosafety
26 October 2021
Third World Network
www.twn.my
Dear Friends and Colleagues
Bt Toxins Targeting Fall Armyworm Affect Its Predator
The fall armyworm, Spodoptera frugiperda, is an agricultural pest from tropical and subtropical regions that causes significant losses in various crops (e.g. maize, cotton, and soybean). The widespread use of Bt crops has resulted in the rapid occurrence of resistance of S. frugiperda to genetically modified (GM) Cry1F maize (TC 1507), affecting field control of this pest in Argentina, Brazil, Puerto Rico and the US. Target insect resistance may be delayed with the use of biological control, including the predator Podisus nigrispinus.
This study evaluated the indirect effects of different Cry proteins on the predatory stink bug P. nigrispinus, with the prey S. frugiperda fed on simple or pyramided Bt maize genotypes. The results showed that different Cry proteins were transferred to P. nigrispinus and promoted histopathological changes in midgut cells of P. nigrispinus. Typical features of cellular degeneration were observed along with the release of cell fragments into the midgut lumen of P. nigrispinus. The latter implies cytotoxic effects causing apoptosis, a morphological pattern of programmed cell death, which may compromise predator fitness.
Conserving natural enemies to improve pest control is a challenge in integrated pest management programmes. Thus, the use of Bt plants needs to be evaluated due to its possible adverse effects on non-target organisms, including beneficial predators.
With best wishes,
Third World Network
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SPODOPTERA FRUGIPERDA (NOCTUIDAE) FED ON TRANSGENIC MAIZE CAN TRANSFER BT PROTEINS TO PODISUS NIGRISPINUS (PENTATOMIDAE)
Michael Willian Rocha de Souza, Marcus Alvarenga Soares,José Eduardo Serrão, Marinalva Martins dos Santos, Caique Menezes de Abreu, Márcia Regina da Costa
Entomology – Sci. agric. (Piracicaba, Braz.) 79 (4) – 2022
https://doi.org/10.1590/1678-992X-2021-0044
23 July 2021
* The fall armyworm, Spodoptera frugiperda, is an agricultural pest original from tropical and subtropical regions and causes significant losses in various crops (e.g. maize, cotton, and soybean). The widespread use of Bt results in the rapid occurrence of resistance of S. frugiperda to Cry1F maize (TC 1507) affecting field control of this pest in Argentina, Brazil, Puerto Rico, and the United States.
ABSTRACT
An important concern with the use of genetically modified plants expressing Bacillus thuringiensis (Bt) insecticidal toxins is the deleterious effect on non-target organisms. The predatory stink bug Podisus nigrispinus (Dallas) is used in biological control programs and may be exposed to Bt toxins. This study evaluated the indirect effects of different Cry proteins on P. nigrispinus with the prey Spodoptera frugiperda, fed on simple or pyramided Bt maize genotypes.
The experiment was carried out in a completely randomized design with three treatments: i) Isohybrid (not Bt), ii) Herculex (transgenic maize encoding Cry1F protein) and iii) PowerCore (pyramidal transgenic maize encoding the Cry1F, Cry1A.105, and Cry2Ab2 proteins), which were used to feed S. frugiperda for 48 h. The caterpillars were used as prey by P. nigrispinus females. We evaluated the presence of Cry proteins, consumed prey biomass (predation), oviposition period, number of postures, number of eggs, number of eggs per posture, number of nymphs, egg viability, embryonic period, female longevity and development, and survival rates of immature.
The results show that different Cry proteins move through the food chain of P. nigrispinus and provide evidence that the ingestion of three different proteins does not lead to unexpected synergistic effects. However, Cry toxins promoted histopathological changes in midgut cells of P. nigrispinus.
Conclusion
Conserving natural enemies to improve pest control is a challenge in integrated pest management programs. Thus, the use of Bt plants needs to be evaluated due to its possible adverse effects on non-target organisms. Our results show that different Cry proteins move through the P. nigrispinus food chain. Besides, the study provides evidence that exposure period of P. nigrispinus females to S. frugiperda that consumed maize leaves expressing Bt toxins has no synergistic effects on the non-target species investigated. However, the Cry1F, Cry1A.105, and Cry2Ab2 toxins consumed by S. frugiperda cause histopathological changes in the midgut of P. nigrispinus (3rd trophic level), which may compromise the predator fitness.