Dose Effects of Flubendiamide and Thiodicarb against Spodoptera Species Developing on Bt and Non-Bt Soybean.

An increase in Spodoptera species was reported in Bt soybean fields expressing Cry1Ac insecticidal proteins in Brazil, requiring additional management with chemical insecticides. Here, we evaluated the dose effects of flubendiamide and thiodicarb on Spodoptera cosmioides (Walker, 1858), Spodoptera eridania (Stoll, 1782), Spodoptera albula (Walker, 1857) and Spodoptera frugiperda (J. E. Smith, 1797) (Lepidoptera: Noctuidae) that survived on MON 87751 × MON 87708 × MON 87701 × MON 89788, expressing Cry1A.105, Cry2Ab2 and Cry1Ac; MON 87701 × MON 89788 soybean, expressing Cry1Ac; and non-Bt soybean. On unsprayed Cry1A.105/Cry2Ab2/Cry1Ac soybean, only S. frugiperda showed ~60% mortality after 10 d, whereas S. cosmioides, S. eridania and S. albula showed >81% mortality. The surviving larvae of all species on this Bt soybean showed >80% mortality when exposed to the field label dose of flubendiamide (70 mL/ha) or thiodicarb (400 g/ha) or at 50% of these doses. In contrast, all four species had <25% and <19% mortality on Cry1Ac and non-Bt soybean, respectively. The surviving S. cosmioides, S. eridania and S. albula on these soybean types presented >83% mortality after exposure to both dose levels of flubendiamide and thiodicarb. Some S. frugiperda larvae surviving on Cry1Ac and non-Bt soybean sprayed with a 50% dose of either insecticide developed into adults. However, the L1 larvae developing on Cry1Ac soybean leaves sprayed with flubendiamide and the L2 larvae on this soybean sprayed with thiodicarb had a prolonged immature stage, and the females displayed lower fecundity, which are likely to impact S. frugiperda population growth on soybean.

Performance of cotton expressing Cry1Ac, Cry1F and Vip3Aa19 insecticidal proteins against Helicoverpa armigera, H. zea and their hybrid progeny, and evidence of reduced susceptibility of a field population of H. zea to Cry1 and Vip3Aa in Brazil.

The genetically modified cotton DAS-21023-5 × DAS-24236-5 × SYN-IR102-7 expressing Cry1Ac, Cry1F and Vip3Aa19 from Bacillus thuringiensis Berliner (Bt) has been cultivated in Brazil since the 2020/2021 season. Here, we assessed the performance of DAS-21023-5 × DAS-24236-5 × SYN-IR102-7 cotton expressing Cry1Ac, Cry1F and Vip3Aa19 against Helicoverpa armigera (Hübner), Helicoverpa zea (Boddie), and their hybrid progeny. We also carried out evaluations with DAS-21023-5 × DAS-24236-5 cotton containing Cry1Ac and Cry1F. In leaf-disk bioassays, DAS-21023-5 × DAS-24236-5 × SYN-IR102-7 was effective in controlling neonates from laboratory colonies of H. armigera, H. zea and the hybrid progeny (71.9%-100% mortality). On floral bud bioassays using L2 larvae, H. zea presented complete mortality, whereas H. armigera and the hybrid progeny showed <55% mortality. On DAS-21023-5 × DAS-24236-5 cotton, the mortality of H. armigera on leaf-disk and floral buds ranged from 60% to 73%, whereas mortality of hybrids was <46%. This Bt cotton caused complete mortality of H. zea larvae from a laboratory colony in the early growth stages, but mortalities were <55% on advanced growth stages and on floral buds. In field studies conducted from 2014 to 2019, DAS-21023-5 × DAS-24236-5 × SYN-IR102-7 cotton was also effective at protecting plants against H. armigera. In contrast, a population of H. zea collected in western Bahia in 2021/2022 on Bt cotton expressing Cry1 and Vip3Aa proteins, showed 63% mortality after 30 d, with insects developing into fifth and sixth instars, on DAS-21023-5 × DAS-24236-5 × SYN-IR102-7 cotton. We conclude that H. armigera, H. zea, and their hybrid progeny can be managed with DAS-21023-5 × DAS-24236-5 × SYN-IR102-7 cotton; however we found the first evidence in Brazil of a significant reduction in the susceptibility to DAS-21023-5 × DAS-24236-5 × SYN-IR102-7 cotton of a population of H. zea collected from Bt cotton in Bahia in 2021/2022.

The bioherbicidal potential of isolated fungi cultivated in microalgal biomass.

This study evaluated the bioherbicidal potential of wild fungi grown on microalgal biomass from the digestate treatment of biogas production. Four fungal isolates were used and the extracts were evaluated for the activity of different enzymes and characterized by gas chromatography coupled with mass spectrometry. The bioherbicidal activity was assessed by application on Cucumis sativus, and the leaf damage was visually estimated. The microorganisms showed potential as agents producing an enzyme pool. The obtained fungal extracts presented different organic compounds, most acids, and when applied to Cucumis sativus, showed high levels of leaf damage (80-100 ± 3.00%, deviation relative to the observed average damage). Therefore, the microbial strains are potential biological control agents of weeds, which, together with the microalgae biomass, offer the appropriate conditions to obtain an enzyme pool of biotechnological relevance and with favorable characteristics to be explored as bioherbicides, addressing aspects within the environmental sustainability.

Characterizing the lethal and sub-lethal effects of genetically modified soybean expressing Cry1A.105, Cry2Ab2, and Cry1Ac insecticidal proteins against Spodoptera species (Lepidoptera: Noctuidae) in Brazil.

BACKGROUND: MON 87701 × MON 89788 × MON 87751 × MON 87708 soybean, that expresses Cry1A.105, Cry2Ab2, and Cry1Ac insecticidal proteins and confers tolerance to glyphosate and dicamba, is a potential tool for managing Spodoptera species in soybean fields in Brazil. In this study, we characterized the lethal and sub-lethal effects of Cry1A.105/Cry2Ab2/Cry1Ac soybean against Spodoptera species and genotypes of Spodoptera frugiperda resistant and susceptible to Cry1 and Cry2 proteins. These evaluations were also conducted with MON 87701 × MON 89788 soybean, which expresses Cry1Ac protein. RESULTS: Cry1A.105/Cry2Ab2/Cry1Ac soybean caused high lethality in neonates of Spodoptera cosmioides and Spodoptera albula. However, it showed low lethality in S. frugiperda genotypes homozygous for resistance to Cry1 and Cry2 proteins but reduced their population growth potential. No relevant lethal effects of Cry1Ac soybean were detected in the Spodoptera species and genotypes evaluated. Spodoptera frugiperda genotypes heterozygous for Cry1 and Cry2 resistance were controlled by Cry1A.105/Cry2Ab2/Cry1Ac soybean, with no insects developing into adults. This Bt soybean also caused intermediate mortality of neonates of Spodoptera eridania (60%-83%) but no surviving larvae developed to adulthood, resulting in population suppression. CONCLUSIONS: Cry1A.105/Cry2Ab2/Cry1Ac soybean caused high mortality of S. cosmioides, S. albula, and S. frugiperda genotypes susceptible to Cry1 and Cry2 and heterozygous for Cry1 and Cry2 resistance. This Bt soybean also suppressed population growth of S. eridania but had minimal impact on S. frugiperda homozygous for resistance to Cry1 and Cry2 proteins. Cry1Ac soybean had minimal impact on all Spodoptera species and genotypes evaluated. © 2022 Society of Chemical Industry.

Development and biological evaluation of nanoencapsulated-based pyrethroids with synergists for resistance management of two soybean pests: insights for new insecticide formulations.

BACKGROUND: Chemical control is commonly used against Euschistus heros (F.) and Chrysodeixis includens (Walker) in soybean fields in South America. However, previous studies reported that these pests have reduced susceptibility to pyrethroids in Brazil. On this basis, we developed and evaluated nanoencapsulated-based bifenthrin (BFT) and λ-cyhalothrin (LAM) with the synergists piperonyl butoxide (PBO) and diethyl maleate (DEM) for insect resistance management (IRM). RESULTS: Nanoformulations of BFT and LAM with PBO and DEM presented good physical-chemical characteristics and were stable. The spherical morphology of all systems and the encapsulation efficiency in nanostructured lipid carriers did not change when synergists were added. Nanoencapsulated BFT with DEM applied topically increased the susceptibility of E. heros to BFT by 3.50-fold. Similarly, nanoencapsulated BFT and LAM with PBO in diet-overlay bioassays increased the susceptibility of C. includens to both chemicals by up to 2.16-fold. Nanoencapsulated BFT and LAM with synergists also improve control efficacy of both species, causing higher mortality than commercial products containing these chemistries. CONCLUSIONS: It is possible to develop nanoencapsulated-based formulations of BFT and LAM with PBO or DEM, and these nanoformulations have the potential to improve control of E. heros and C. includens with recognized low susceptibility to pyrethroids. This study provides updates for designing new insecticide formulations for IRM. © 2022 Society of Chemical Industry.

Influence of adjuvants added to teflubenzuron spray on resistant and susceptible strains of the soybean looper Chrysodeixis includens (Lepidoptera: Noctuidae) / Influência da adição de adjuvantes à calda de pulverização de teflubenzuron em linhagens resistentes e suscetíveis da lagarta falsa-medideira Chrysodeixis includens em soja (Lepidoptera: Noctuidae)

The soybean looper (SBL), Chrysodeixis includens (Walker, [1858]) (Lepidoptera: Noctuidae), is a soybean and cotton pest in South America countries. Field-evolved resistance of SBL to inhibitors of chitin biosynthesis has been reported in Brazil; however, this mode of action is still widely used against SBL. On this basis, we conducted laboratory bioassays to investigate if adjuvants (Nimbus®, TA 35®, Break-Thru® S 240, and Rizospray Extremo®) added to the teflubenzuron spray increase the mortality of SBL strains (resistant, heterozygous, and susceptible to chitin biosynthesis inhibitors). Using chromatography analysis, we also evaluated the amount of teflubenzuron on soybean leaves when applied alone or in combination with adjuvants. In laboratory bioassays, the biological activity of teflubenzuron increased against the susceptible SBL strain when adjuvants were added. In contrast, no relevant effects of adjuvants added to the teflubenzuron spray against heterozygous and resistant SBL larvae were detected. In leaf bioassays, even leaves from the upper third part of the plants containing a significantly higher amount of teflubenzuron (3.4 mg/kg vs 1.7 and 0.6 mg/kg); the mortality of SBL strains was similar when teflubenzuron was applied alone or in mixture with adjuvants. Our findings indicated that adjuvants added to teflubenzuron spray do not provide a substantial increase in the mortality of SBL strains resistant to chitin biosynthesis inhibitors. Therefore, it is necessary to reduce the use of this mode-ofaction insecticide against SBL and to give preference to other insecticides or control tactic.

A lagarta falsa-medideira, Chrysodeixis includens (Walker, [1858]) (Lepidoptera: Noctuidae), é uma praga da soja e do algodão nos países da América do Sul. A resistência de C. includens a inibidores da biossíntese de quitina tem sido relatada no Brasil. Entretanto, esse modo de ação ainda é amplamente utilizado para controle de C. includens. Com base nisso, conduzimos bioensaios em laboratório para investigar se adjuvantes (Nimbus®, TA 35®, Break-Thru® S 240 e Rizospray Extremo®) adicionados à calda inseticida de teflubenzuron aumentam a mortalidade de linhagens de C. includens (resistentes, heterozigotos e suscetíveis a inibidores da biossíntese de quitina). Usando análise cromatográfica, também avaliamos a quantidade de teflubenzuron em folhas de soja quando aplicado isolado ou em combinação com adjuvantes. Em bioensaios de laboratório, a atividade biológica do teflubenzuron aumentou para a linhagem suscetível quando os adjuvantes foram adicionados à calda inseticida. Em contraste, nenhum efeito relevante de adjuvantes adicionados ao teflubenzuron foi detectado para os heterozigotos e resistentes. Em bioensaios de folhas, mesmo naquelas do terço superior das plantas, as quais apresentaram uma maior deposição de teflubenzuron (3,4 mg/kg vs 1,7 e 0,6 mg/kg); a mortalidade das linhagens de C. includens foi semelhante quando o teflubenzuron foi aplicado isolado ou com adjuvantes. Nossos resultados indicam que os adjuvantes adicionados ao teflubenzuron não fornecem um aumento substancial na mortalidade de linhagens de C. includens resistentes aos inibidores da biossíntese de quitina. Portanto, é necessário reduzir o uso desse modo de ação para o manejo de C. includens e dar preferência a outros inseticidas ou tática de controle.

Regional pest suppression associated with adoption of Cry1Ac soybean benefits pest management in tropical agriculture.

BACKGROUND: Bacillus thuringiensis (Bt) crops have been adopted worldwide, providing high-level protection from insect pests. Furthermore, Bt crops preserve natural enemies, promote higher yield, and economically benefit farmers. Although regional pest suppression by widespread Bt crop adoption has been observed in temperate regions, this possibility remains uncertain in tropical areas due to the high diversity of alternative hosts and mild winters. RESULTS: Evidence of regional reduction in insecticide use across areas was observed in Brazil where Cry1Ac soybean has been grown since 2013, with up to 50% reduction in the number of insecticide sprays for managing lepidopteran pests on non-Bt soybean observed at specific locations from 2012 to 2019. Pest monitoring data from four mesoregions across 5 years of commercial plantings of Cry1Ac soybean from December 2014 to July 2019 showed reduced numbers of Chrysodeixis includens moths captured in pheromone traps across years at all locations. The number of Helicoverpa spp. moths captured also was reduced at three locations. CONCLUSION: We provide evidence for regional suppression of lepidopteran pests and reduced insecticide use with the widespread adoption of Cry1Ac soybean in Brazil, bringing economic, social and environmental benefits. © 2022 Society of Chemical Industry.

Intra- and Interspecific Variation in the Susceptibility to Insecticides of Stink Bugs (Hemiptera: Pentatomidae) That Attack Soybean and Maize in Southern Brazil.

This study evaluated intra- and interspecific variation regarding the susceptibility to insecticides of key pentatomid pests of soybean (Glycine max L.) and maize (Zea mays L.) crops in Brazil. To perform bioassays, populations of Euschistus heros (F.), Diceraeus (=Dichelops) furcatus (F.), Nezara viridula (L.), and Piezodorus guildinii (Westwood) (Hemiptera: Pentatomidae) were collected in soybean fields in Southern Brazil during the 2020/2021 crop season. Then, stink bugs were exposed to doses of commercial insecticides commonly applied for its control in dip-test bioassays using fresh green bean pods. In general, all stink bug species and populations studied were susceptible to acephate, acetamiprid + bifenthrin, imidacloprid + bifenthrin, and ethiprole, with mortality rates > 80%. Most populations of E. heros and D. furcatus, considered the main stink bugs that attack soybean and maize, respectively, presented low or intermediate susceptibility to acetamiprid + α-cypermethrin, ζ-cypermethrin + bifenthrin, dinotefuran + λ-cyhalothrin, and bifenthrin + carbosulfan. Except for bifenthrin + carbosulfan (mortality < 57%), secondary stink bugs species that attack soybean (N. viridula and P. guildinii) showed pronounced susceptibility to all insecticides tested, with mortality rates > 70%. In summary, the populations of E. heros and D. furcatus showed diminished susceptibility to various insecticides formulated with the mixture of neonicotinoids + pyrethroids, whereas N. viridula and P. guildinii were most susceptible to the insecticides evaluated. The implications of these findings to integrated and resistance management programs are discussed.

The Effect of Synergistic Compounds on the Susceptibility of Euschistus heros (Hemiptera: Pentatomidae) and Chrysodeixis includens (Lepidoptera: Noctuidae) to Pyrethroids.

The Neotropical brown stink bug, Euschistus heros (F.), and the soybean looper, Chrysodeixis includens (Walker), are key pests of soybean in South America. Low susceptibility to pyrethroids has been reported for both species in Brazil. Here, we evaluate the addition of synergistic compounds piperonyl butoxide (PBO) and diethyl maleate (DEM) to manage E. heros and C. includens with resistance to λ-cyhalothrin and bifenthrin. The LD50 of technical grade and commercial products containing λ-cyhalothrin and bifenthrin decreased against field-collected E. heros exposed to PBO and DEM relative to unexposed insects; synergistic ratios up to 4.75-fold. The mortality also increased when E. heros were exposed to commercial formulations containing λ-cyhalothrin (from 4 to 44%) and bifenthrin (from 44 to 88%) in the presence of synergists. There was also a higher susceptibility of field-collected C. includens to technical grade λ-cyhalothrin when PBO was used; synergistic ratio of 5.50-fold. High lethally of technical grade λ-cyhalothrin was also verified in the presence of PBO, with mortality increasing from 6 to 57%. Our findings indicate the potential utility of synergists in reversing the resistance to λ-cyhalothrin and bifenthrin in E. heros and C. includens and suggest a significant role of metabolic mechanisms underlying the detoxification of both pyrethroids.

Interspecific Variation in Susceptibility to Insecticides by Lepidopteran Pests of Soybean, Cotton, and Maize Crops From Brazil.

The interspecific variation in susceptibility to insecticides by lepidopteran species of soybean [Glycine max L. (Merr.)], cotton (Gossypium hirsutum L.), and maize (Zea mays L.) crops from Brazil were evaluated. Populations of Anticarsia gemmatalis (Hübner) (Lepidoptera: Erebidae), Chrysodeixis includens (Walker), Helicoverpa armigera (Hübner), Spodoptera frugiperda (Smith), Spodoptera eridania (Stoll), Spodoptera cosmioides (Walker), and Spodoptera albula (Walker) (Lepidoptera: Noctuidae) were collected from 2019 to 2021. Early L3 larvae (F2 generation) were exposed to the formulated insecticides methoxyfenozide, indoxacarb, spinetoram, flubendiamide, and chlorfenapyr in diet-overlay bioassays. The median lethal concentrations (LC50) were used to calculate tolerance ratios (TR) of each species in relation to the most susceptible species to each insecticide. The lowest LC50 values were verified for A. gemmatalis to all insecticides tested. Chrysodeixis includens and most of the Spodoptera species were moderately tolerant to methoxyfenozide (TR < 8.0-fold) and indoxacarb (TR < 39.4-fold), whereas H. armigera was the most tolerant species to methoxyfenozide (TR = 21.5-fold), and indoxacarb (TR = 106.4-fold). Spodoptera cosmioides, S. eridania, and S. albula showed highest tolerance to spinetoram (TR > 1270-fold), S. eridania, S. frugiperda, and S. albula to flubendiamide (TR from 38- to 547-fold), and S. albula to indoxacarb (TR = 138.6-fold). A small variation in susceptibility to chlorfenapyr (TR < 4.4-fold) was found among the lepidopteran evaluated. Our findings indicate a large variation in susceptibility to indoxacarb, spinetoram, and flubendiamide and a relatively low variation in susceptibility to methoxyfenozide and chlorfenapyr by lepidopteran species of soybean, cotton, and maize from Brazil.

Assessing fitness costs of the resistance of Spodoptera frugiperda (Lepidoptera: Noctuidae) to pyramided Cry1 and Cry2 insecticidal proteins on different host plants.

Fall armyworm (FAW), Spodoptera frugiperda (Smith), is one of the major pests targeted by transgenic crops expressing insecticidal proteins from Bacillus thuringiensis (Bt) Berliner. However, FAW presents a high capacity to develop resistance to Bt protein-expressing crop lines, as reported in Brazil, Argentina, Puerto Rico and the southeastern U.S. Here, FAW genotypes resistant to pyramided maize events expressing Cry1F/Cry1A.105/Cry2Ab2 (P-R genotype) and Cry1A.105/Cry2Ab2 (Y-R genotype) from Brazil were used to investigate the interactions between non-Bt hosts (non-Bt maize, non-Bt cotton, millet and sorghum) and fitness costs. We also tested a FAW genotype susceptible to Bt maize and F1 hybrids of the resistant and susceptible genotypes (heterozygotes). Recessive fitness costs (i.e., costs affecting the resistant insects) were observed for pupal and neonate to adult survival of the P-R genotype on non-Bt cotton; larval developmental time of the P-R genotype on millet and sorghum; larval and neonate-to-adult developmental time of the Y-R genotype on non-Bt cotton and sorghum; the fecundity of the Y-R genotype on non-Bt cotton; and mean generation time of both resistant genotypes. However, on non-Bt cotton and non-Bt maize, the P-R genotype had a higher fitness (i.e., fitness benefits), displaying greater fecundity and rates of population increases than the Sus genotype. Non-recessive fitness costs (i.e., costs affecting heterozygotes) were found for fecundity and population increases on millet and sorghum. These findings suggest that, regardless of the disadvantages of the resistant genotypes in some hosts, the resistance of FAW to Cry1 and Cry2 Bt proteins is not linked with substantial fitness costs, and may persist in field conditions once present.

Resistance status of lepidopteran soybean pests following large-scale use of MON 87701 × MON 89788 soybean in Brazil.

Widespread adoption of MON 87701 × MON 89788 soybean, expressing Cry1Ac Bt protein and glyphosate tolerance, has been observed in Brazil. A proactive program was implemented to phenotypically and genotypically monitor Cry1Ac resistance in Chrysodeixis includens (Walker). Recent cases of unexpected injury in MON 87701 × MON 89788 soybean were investigated and a large-scale sampling of larvae on commercial soybean fields was performed to assess the efficacy of this technology and the distribution of lepidopteran pests in Brazil. No significant shift in C. includens susceptibility to Cry1Ac was observed eight years after commercial introduction of this technology in Brazil. F2 screen results confirmed that the frequency of Cry1Ac resistance alleles remains low and stable in C. includens. Unexpected injury caused by Rachiplusia nu (Guenée) and Crocidosema aporema (Walsingham) in MON 87701 × MON 89788 soybean was detected during the 2020/21 season, and studies confirmed a genetically based alteration in their susceptibility to Cry1Ac. MON 87701 × MON 89788 soybean remains effective against Anticarsia gemmatalis (Hübner), C. includens, Chloridea virescents (Fabricius) and Helicoverpa armigera (Hübner) in Brazil. However, there is evidence of field-evolved resistance to MON 87701 × MON 89788 soybean by the secondary soybean pests R. nu and C. aporema.

Pathogenic Assessment of SfMNPV-Based Biopesticide on Spodoptera frugiperda (Lepidoptera: Noctuidae) Developing on Transgenic Soybean Expressing Cry1Ac Insecticidal Protein.

Pathogenic assessment of a baculovirus-based biopesticide containing Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV: Baculoviridae: Alphabaculovirus) infecting fall armyworm, Spodoptera frugiperda (J. E. Smith, 1797) (Lepidoptera: Noctuidae) is reported. In the bioassays, neonates were infected with different doses of SfMNPV applied on Cry1Ac Bt soybean and non-Bt soybean. Our findings indicated that S. frugiperda neonates did not survive at 10 d post infection or develop into adults on Bt and non-Bt soybean sprayed with the field recommended dose of SfMNPV. In contrast, a proportion of the infected neonates developed into adults when infected with lower doses of SfMNPV (50%, 25%, and 10% of field dose) in both Bt and non-Bt soybean. However, S. frugiperda neonates surviving infection at the lowest virus doses on both soybean varieties showed longer neonate-to-pupa and neonate-to-adult periods, lower larval and pupal weights, reduced fecundity, and increased population suppression. Nevertheless, more pronounced pathogenicity of SfMNPV infecting neonates of S. frugiperda were verified on larvae that developed on Bt soybean. These findings revealed that, beyond mortality, the biopesticide containing SfMNPV also causes significant sublethal pathogenic effects on neonates of S. frugiperda developing on Bt and non-Bt soybean and suggested an additive effect among SfMNPV and Cry1Ac insecticidal protein expressed in Bt soybean.

Inheritance patterns, cross-resistance and synergism in Spodoptera frugiperda (Lepidoptera: Noctuidae) resistant to emamectin benzoate.

BACKGROUND: Fall armyworm, Spodoptera frugiperda (J. E. Smith), is a relevant global pest due to severe damage caused on agricultural crops and its capacity to evolve resistance to insecticides. Here, we selected a strain of S. frugiperda resistant to emamectin benzoate under laboratory conditions to understand the inheritance patterns, cross-resistance and synergism involved in the resistance. RESULTS: The emamectin benzoate-resistant (Ben-R) strain was isolated by using F2 screen in a field population collected in Lucas do Rio Verde, Mato Grasso state, Brazil. After ten generations of selection pressure with emamectin benzoate, the estimated LC50 of the Ben-R strain was 678.38 µg a.i. mL-1 whereas that of the susceptible (Sus) strain was 0.29 µg a.i.mL-1 , resulting in a resistance ratio (RR) of ~ 2340-fold. The LC50 values of the offspring from reciprocal crosses of Sus and Ben-R strains were 93.37 and 105.32 µg a.i. mL-1 , suggesting that resistance is an autosomal incompletely dominant trait. The high survival of heterozygous and Ben-R strains (>92%) on non-Bt maize sprayed with the field rate of emamectin benzoate confirmed that resistance is functionally dominant. The minimum number of segregations influencing resistance was 3.55, suggesting a polygenic effect. Low cross-resistance was detected between emamectin benzoate and the insecticides methomyl, chlorpyrifos, lambda-cyhalothrin, spinetoram, indoxacarb and chlorantraniliprole (RR <5.75-fold). There was no effect of synergists piperonyl butoxide, diethyl maleate and S, S, S-tributyl phosphorotrithiotate on the Ben-R strain, suggesting a minor role of metabolic resistance. CONCLUSIONS: Our results showed a high risk of resistance evolution of S. frugiperda to emamectin benzoate, based on incompletely dominant inheritance. Rotation of insecticides with different modes of action can be one of the resistance management strategies to be implemented to delay the evolution of resistance of S. frugiperda to emamectin benzoate in Brazil.

Field-evolved resistance to chlorpyrifos by Spodoptera frugiperda (Lepidoptera: Noctuidae): Inheritance mode, cross-resistance patterns, and synergism.

BACKGROUND: Fall armyworm (FAW), Spodoptera frugiperda (Smith), is an economically important pest worldwide. In this study, we selected a genotype of FAW resistant to chlorpyrifos from a field-collected population, characterized the genetic basis of resistance, and evaluated cross-resistance and mechanisms of resistance using synergists. RESULTS: The LD50 values of chlorpyrifos for the resistant (Clorp-R) and susceptible (Sus) FAW genotypes were 24.26 and 0.023 µg per larva, respectively, representing a resistance ratio > 1050-fold. The LD50 values of chlorpyrifos against heterozygotes were 3.34 and 4.00 µg per larva, suggesting that resistance is autosomally inherited. The chlorpyrifos resistance in FAW was influenced by few genes, with the minimum numbers of segregations being 1.74 and 1.88. On chlorpyrifos-sprayed plants and leaves, Clorp-R and heterozygote genotypes showed >95% and >52% survival, respectively, whereas the Sus genotype had no survival, indicating that the resistance is incompletely dominant at the field rate of chlorpyrifos. The Clorp-R genotype presented some cross-resistance to acephate, but low cross-resistance to thiodicarb, methomyl, chlorfenapyr, flubendiamide, methoxyfenozide, spinetoram, and teflubenzuron. The synergists piperonyl butoxide, diethyl maleate, and S,S,S-tributyl phosphorotrithiotate did not have relevant effects on the Clorp-R genotype, suggesting a minor role for metabolic resistance. CONCLUSIONS: The inheritance of chlorpyrifos resistance in FAW was characterized as autosomal, incompletely dominant, and polygenic, with metabolic resistance playing a small role in the detoxification of chlorpyrifos. Low cross-resistance between chlorpyrifos and other mode of action (MoA) insecticides occurs in FAW, highlighting the importance of considering the rotation of MoA as a strategy to delay resistance. © 2021 Society of Chemical Industry.

Fitness Cost of Chlorpyrifos Resistance in Spodoptera frugiperda (Lepidoptera: Noctuidae) on Different Host Plants.

Spodoptera frugiperda (J. E. Smith, 1797) is a polyphagous pest of global relevance due to the damage it inflicts on agricultural crops. In South American countries, this species is one of the principal pests of maize and cotton. Currently, S. frugiperda is also emerging as an important pest of soybeans and winter cereals in Brazil. Chemical control is one of the main control tactics against S. frugiperda, even though resistance against numerous modes of action insecticides has been reported. To support insect resistance management programs, we evaluated the fitness costs of resistance of S. frugiperda to the acetylcholinesterase inhibitor chlorpyrifos. Fitness costs were quantified by comparing biological parameters of chlorpyrifos-resistant and -susceptible S. frugiperda and their F1 hybrids (heterozygotes) on non-Bt cotton, non-Bt maize, non-Bt soybean, and oats. The results revealed that the chlorpyrifos-resistant genotype showed lower pupa-to-adult and egg-to-adult survivorship and reduced larval weights on oats; longer neonate-to-pupa and egg-to-adult developmental periods, and lower pupal weights and fecundity on maize; lower pupal weights on soybean; and reduced fecundity on cotton compared with the chlorpyrifos-susceptible genotype. Fitness costs also affected fertility life table parameters of the resistant genotype, increasing the mean length of a generation on cotton and maize and reducing the potential for population growth on all hosts. These findings suggest fitness costs at the individual and population levels of chlorpyrifos resistance in S. frugiperda, indicating that removal of the selective agent from the environment would result in reduced resistance and opportunities for the restoration of susceptibility.

Susceptibility of Brazilian Populations of Anastrepha fraterculus, Ceratitis capitata (Diptera: Tephritidae), and Drosophila suzukii (Diptera: Drosophilidae) to Selected Insecticides.

Anastrepha fraterculus (Wiedemann), Ceratitis capitata (Wiedemann), and Drosophila suzukii (Matsumura) are the main fruit pests in Brazil. Here, we evaluated the susceptibility of Brazilian populations of A. fraterculus, C. capitata, and D. suzukii to selected insecticides. In ingestion bioassays, adults from a laboratory susceptible population of each species were exposed to five different modes of action of insecticide. Then, field populations of each species were exposed to the diagnostic concentrations to evaluate possible changes in susceptibility. Our findings indicate that lambda-cyhalothrin, malathion, and spinosad had similar levels of toxicity against a susceptible laboratory population of A. fraterculus, with LC50 values of 6.34, 6.54, and 8.76 µg a.i./ml, respectively. Ceratitis capitata had similar susceptibilities to spinosad (1.30 µg a.i./ml), spinetoram (2.76 µg a.i./ml), and malathion (7.10 µg a.i./ml), but a lower susceptibility to lambda-cyhalothrin (76.55 µg a.i./ml). For D. suzukii, the LC50 values of deltamethrin (0.67 µg a.i./ml), malathion (3.30 µg a.i./mL), spinosad (4.16 µg a.i./ml), and spinetoram (4.75 µg a.i./ml) were lower than for abamectin (15.02 µg a.i./ml), acetamiprid (39.38 a.i./ml), and thiamethoxam (70.15 µg a.i./ml). The diagnostic concentrations, based on LC99 values of the insecticides, caused more than 99% mortality for most field populations of each species. For lambda-cyhalothrin the populations RS-1 (A. fraterculus) and SC (C. capitata) showed approximately 10% of live insects. These differences represent the natural variation in population susceptibility and not due to insecticide selection pressure. The diagnostic concentrations defined here should be used in future resistance monitoring programs in Brazil.

Transcriptome Analysis of Pyrethroid-Resistant Chrysodeixis includens (Lepidoptera: Noctuidae) Reveals Overexpression of Metabolic Detoxification Genes.

Chrysodeixis includens (Walker, [1858]) is one of the most important defoliator of soybean in Brazil because of its extensive geographical distribution and high tolerance to insecticides compared with other species of caterpillars. Because of this, we conducted bioassays to evaluate the efficacy of pyrethroid λ-cyhalothrin on a C. includens resistant strain (MS) and a susceptible (LAB) laboratory strain. High throughput RNA sequencing (RNA-seq) of larval head and body tissues were performed to identify potential molecular mechanisms underlying pyrethroid resistance. Insecticide bioassays showed that MS larvae exhibit 28.9-fold resistance to pyrethroid λ-cyhalothrin relative to LAB larvae. RNA-seq identified evidence of metabolic resistance in the head and body tissues: 15 cytochrome P450 transcripts of Cyp6, Cyp9, Cyp4, Cyp304, Cyp307, Cyp337, Cyp321 families, 7 glutathione-S-transferase (Gst) genes, 7 α-esterase genes from intracellular and secreted catalytic classes, and 8 UDP-glucuronosyltransferase (Ugt) were overexpressed in MS as compared with LAB larvae. We also identified overexpression of GPCR genes (CiGPCR64-like and CiGPCRMth2) in the head tissue. To validate RNA-seq results, we performed RT-qPCR to assay selected metabolic genes and confirmed their expression profiles. Specifically, CiCYP9a101v1, CiCYP6ae149, CiCYP6ae106v2, CiGSTe13, CiCOE47, and CiUGT33F21 exhibited significant overexpression in resistant MS larvae. In summary, our findings detailed potential mechanisms of metabolic detoxification underlying pyrethroid resistance in C. includens.

Performance of Genetically Modified Soybean Expressing the Cry1A.105, Cry2Ab2, and Cry1Ac Proteins Against Key Lepidopteran Pests in Brazil.

The pyramided genetically modified (GM) soybean [Glycine max L. (Merr.)] MON87751 × MON87708 × MON87701 × MON89788, expressing Cry1A.105, Cry2Ab2, and Cry1Ac from Bacillus thuringiensis Berliner, was approved for commercial use in Brazil. We conducted laboratory, greenhouse, and field studies to assess the efficacy of this Bt soybean against key soybean lepidopteran pests. Neonates of Anticarsia gemmatalis (Hübner) (Lepidoptera: Erebidae), Chrysodeixis includens (Walker), and Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) were exposed to Bt proteins in diet-overlay bioassays. MON87751 × MON87708 × MON87701 × MON89788 soybean and individual components were evaluated in laboratory (leaf disc), greenhouse (high artificial infestations), and in field conditions (natural infestations). Neonates of A. gemmatalis, C. includens, and H. armigera were highly susceptible to Cry1A.105 (LC50 from 0.79 to 48.22 ng/cm2), Cry2Ab2 (LC50 from 1.24 to 8.36 ng/cm2), and Cry1Ac (LC50 from 0.15 to 5.07 ng/cm2) in diet-overlay bioassays. In laboratory leaf disc bioassays and greenhouse trials, MON87751 × MON87708 × MON87701 × MON89788 soybean as well as the individual components were highly effective in controlling A. gemmatalis, C. includens, and H. armigera. Similarly, under field conditions, the pyramided genotypes expressing Cry1A.105, Cry2Ab2, and Cry1Ac were highly effective at protecting soybean against C. includens. We concluded that the individual Bt proteins expressed by GM soybean MON87751 × MON87708 × MON87701 × MON89788 killed all or nearly all the susceptible A. gemmatalis, C. includens, and H. armigera, fulfilling one important criterion for successfully delaying resistance to pyramided Bt crops.

Performance of Seed Treatments Applied on Bt and Non-Bt Maize Against Fall Armyworm (Lepidoptera: Noctuidae).

Fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), is the main pest of maize in Brazil, attacking plants from emergence to reproductive stages. Here, we conducted studies to evaluate the efficacy of two seed treatments (chlorantraniliprole alone and imidacloprid combined with thiodicarb) on Bt and non-Bt maize in laboratory bioassays with distinct FAW strains that are susceptible, selected for resistance to Bt-maize single (Cry1F) or pyramided (Cry1A.105 + Cry2Ab2) events and F1 hybrids of the selected and susceptible strains (heterozygotes), and in the field against a natural infestation. In the laboratory, leaf-discs from seed treated Bt-maize plants at 7 d after emergence (DAE) increased the mortality of FAW resistant, heterozygote, and susceptible strains up to 24.8%, when compared with the respective maize grown without a seed treatment. In the field against natural infestations of FAW, Bt maize with a seed treatment had ~30% less FAW damage than non-Bt maize with the same seed treatment at 7 and 14 DAE. No differences in FAW damage was observed between Bt and non-Bt maize grown with and without a seed treatment at 21 DAE. Maize seeds treated with chlorantraniliprole alone or imidacloprid and thiodicarb combined presented limited protection against early infestations of FAW strains under laboratory and field studies.