Owlet moths (Lepidoptera: Noctuoidea) associated with Bt and non- Bt soybean in the brazilian savanna

The role of genetically engineered soybean and Amaranthus weeds on biological and reproductive parameters of Spodoptera cosmioides (Lepidoptera: Noctuidae)

BACKGROUND

In soybean fields containing insecticide- and herbicide-resistant genetically engineered varieties, some weed species have increasingly become difficult to manage and may favor the population growth of secondary pests like Spodoptera cosmioides (Walker) (Lepidoptera: Noctuidae). To test this hypothesis, we measured life-history traits, population growth parameters and adult nutrient content of S. cosmioides reared on foliage from four Amaranthus species, from Cry1Ac Bt and non-Bt soybean varieties, and on meridic artificial diet.

RESULTS

Larvae reared on A. palmeri and A. spinosus had a shorter development time (5-7 days) than larvae raised on the soybean varieties and A. hybridus. Armyworm survival probability was zero on A. viridis and highest (80% and 71%) on soybeans and A. palmeri. The latter and the artificial diet produced the heaviest larvae and pupae, in contrast to the non-Bt soybean variety. Body nutrient content diverged mostly for adults reared on artificial diet compared with those raised on the soybean varieties. The intrinsic rate of population increase (overall fitness) was 27.88% higher for the armyworms on A. palmeri, Cry1Ac Bt soybean and artificial diet compared with those on non-Bt soybean, A. spinosus and A. hybridus.

CONCLUSIONS

Cry1Ac soybean fields infested by some Amaranthus weeds, especially A. palmeri, are conducive to the population growth of S. cosmioides. Integrated pest management programs may be needed to properly manage S. cosmioides in soybean fields, with surveillance for population peaks and judicious control measures when needed. © 2022 Society of Chemical Industry.

Large-scale assessment of lepidopteran soybean pests and efficacy of Cry1Ac soybean in Brazil

The soybean technology MON 87701 × MON 89788, expressing Cry1Ac and conferring tolerance to glyphosate, has been widely adopted in Brazil since 2013. However, pest shifts or resistance evolution could reduce the benefits of this technology. To assess Cry1Ac soybean performance and understand the composition of lepidopteran pest species attacking soybeans, we implemented large-scale sampling of larvae on commercial soybean fields during the 2019 and 2020 crop seasons to compare with data collected prior to the introduction of Cry1Ac soybeans. Chrysodeixis includens was the main lepidopteran pest in non-Bt fields. More than 98% of larvae found in Cry1Ac soybean were Spodoptera spp., although the numbers of Spodoptera were similar between Cry1Ac soybean and non-Bt fields. Cry1Ac soybean provided a high level of protection against Anticarsia gemmatalis, C. includens, Chloridea virescens and Helicoverpa spp. Significant reductions in insecticide sprays for lepidopteran control in soybean were observed from 2012 to 2019. Our study showed that C. includens and A. gemmatalis continue to be primary lepidopteran pests of soybean in Brazil and that Cry1Ac soybean continues to effectively manage the target lepidopteran pests. However, there was an increase in the relative abundance of non-target Spodoptera spp. larvae in both non-Bt and Cry1Ac soybeans.

The hotter the better? Climate change and voltinism of Spodoptera eridania estimated with different methods

Substantial increases in global temperature are projected for the coming decades due to climate change. Considering that temperature has a strong influence on insect voltinism (i.e., number of generations per year), climate change may affect the population growth of insects, with potential consequences for food production. The southern armyworm, Spodoptera eridania, is a multivoltine species native to the American tropics that causes severe damage to several crops. In this context, this study evaluated the impacts of climate change on the voltinism of S. eridania in southern Brazil. Current and future daily temperature data were combined with non-linear and degree-day models to estimate the voltinism of this pest. Under current climate conditions, the voltinism of S. eridania ranged from 2.9 to 9.2 generations, with fewer cohorts in colder regions and more in warmer ones. A higher number of generations was predicted for the future climate scenarios evaluated, reaching up to 12.1 annual generations in certain regions by 2070. Most of the variation in voltinism was explained by location (87.7%) and by the interaction between location and mathematical model (3.0%). The degree-day model estimated an increase in the number of generations in the entire study area, while the non-linear model predicted a decrease in voltinism in the warmer regions under future climate change scenarios. Given these differences between the predictions provided by degree-day and non-linear models, the selection of the best method to be used in climate change studies should be carried out carefully, considering how species respond to temperature. A considerable increase in the number of generations of S. eridania was projected for most of the study area under the climate change scenarios evaluated, suggesting a possible rise in pest incidence levels in the coming decades.

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) in Brazil: the Big Outbreak Monitored by Light Traps

The first detection of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) in Brazil pointed to a gloomy future for South American agriculture in the 2012/2013 harvest, and insecticide sales increased exponentially during 2013 and 2014. However, after this outbreak, the population of this insect returned to manageable levels. This study documents data on H. armigera moth collection using light traps during the outbreak in two locations: (a) western region of the state of Bahia, including population levels of H. armigera and main noctuid pests during the big outbreak (February and March 2013); (b) Federal District, including monthly data for five growing seasons (July 2012-June 2017). During the outbreak, an average of 527.3 moths were collected per trap (cotton crop, March) in the western region of Bahia each night, while the maximum average in the Federal District was 75.4 moths (January). The number of moths decreased in the following growing seasons, and in October 2016, the maximum number was 2.8 moths per trap. Aspects related to the variations of H. armigera and Helicoverpa zea (Boddie) populations, including the study of phenology and relationship with climatic factors and Oceanic Niño Index, were analyzed and discussed. All aspects are approached to contribute to the management of lepidopteran pests, especially H. armigera, in the productive systems of the Brazilian Cerrado.

Survival and development of Spodoptera eridania, Spodoptera cosmioides and Spodoptera albula (Lepidoptera: Noctuidae) on genetically-modified soybean expressing Cry1Ac and Cry1F proteins

BACKGROUND

Spodoptera eridania (Stoll), S. cosmioides (Walker) and S. albula (Walker) (Lepidoptera: Noctuidae) are considered secondary pests of soybean in South America. The genetically-modified soybean DAS-444Ø6-6 × DAS-81419-2 with tolerance to 2,4-dichlorophenoxyacetic acid (2,4-D), glyphosate and ammonium glufosinate herbicides (event DAS-444Ø6-6) and insect-resistance due to expression of Cry1Ac and Cry1F Bt proteins (event DAS-81419-2) may provide a potential tool for integrated pest management (IPM) of these species in soybean fields. Based on this, we conducted bioassays to evaluate the survival and development of S. eridania, S. cosmioides and S. albula fed on Cry1Ac/Cry1F-soybean leaf tissue.

RESULTS

Spodoptera eridania and S. cosmioides fed on Cry1Ac/Cry1F-soybean showed longer developmental time, lower larval and egg to adult survival compared to those fed on non-Bt soybean, reducing the population growth of these species. Spodoptera albula also had lower larval survival and number of insects that reached adulthood on Cry1Ac/Cry1F-soybean. However, no significant effects of Cry1Ac/Cry1F-soybean on population growth parameters were detected in this species.

CONCLUSIONS

Soybean with stacked events DAS-444Ø6-6 × DAS-81419-2 expressing Cry1Ac/Cry1F Bt proteins provide population suppression of S. eridania and S. cosmioides. However, this Bt soybean had minimal effects on S. albula, and is unlikely to have negative population-level effects on this species. It is expected that under field conditions, other control tactics must be integrated with Cry1Ac/Cry1F-soybean for the management of these Spodoptera species. © 2020 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.