Characterizing the differential susceptibility and resistance to insecticides in populations of Chrysodeixis includens and Rachiplusia nu (Lepidoptera: Noctuidae) in Brazil.

BACKGROUND: Chrysodeixis includens (Walker) and Rachiplusia nu (Guenée) are major Plusiinae pests of soybean in the Southern Cone region of South America. In recent decades, C. includens was the main defoliator of soybean in Brazil, but from 2021 onwards, R. nu emerged as an important soybean pest in various regions of the country. Here, we characterize the differential susceptibility and resistance to insecticides in these Plusiinae pests from two soybean regions of Brazil. RESULTS: Except for spinetoram and chlorfenapyr (comparable lethality against both species) and a Bt-based biopesticide (more lethal for C. includens), the tested insecticides showed higher lethality against R. nu than against C. includens, but populations of the same species, even separated by long distances, presented similar resistance levels. For both species, the 90% lethal concentration (LC90) values of most insecticides were higher than the field-recommended dose. Nevertheless, the field-recommended doses of spinetoram, metaflumizone, emamectin benzoate, cyclaniliprole and chlorfenapyr showed comparable control efficacy against both species, whereas indoxacarb, chlorantraniliprole, flubendiamide, teflubenzuron and chlorfluazuron were more lethal for R. nu, and methoxyfenozide and the Bt-based insecticide were more lethal for C. includens. Thiodicarb, methomyl and lambda-cyhalothrin showed low lethality against both species. CONCLUSIONS: Large interspecific differences in the susceptibility to insecticides was found in major Plusiinae pests of soybean in Brazil. Furthermore, variations in susceptibility to insecticides occurred consistently among species and populations, regardless of the collection site and thus despite unequal temporal and spatial exposure to insecticides. These results demonstrate that accurate species identification is essential for effective control of Plusiinae in soybean. © 2024 Society of Chemical Industry.

Predation on sentinel prey increases with increasing latitude in Brassica-dominated agroecosystems.

In natural ecosystems, arthropod predation on herbivore prey is higher at lower latitudes, mirroring the latitudinal diversity gradient observed across many taxa. This pattern has not been systematically examined in human-dominated ecosystems, where frequent disturbances can shift the identity and abundance of local predators, altering predation rates from those observed in natural ecosystems. We investigated how latitude, biogeographical, and local ecological factors influenced arthropod predation in Brassica oleracea-dominated agroecosystems in 55 plots spread among 5 sites in the United States and 4 sites in Brazil, spanning at least 15° latitude in each country. In both the United States and Brazil, arthropod predator attacks on sentinel model caterpillar prey were highest at the highest latitude studied and declined at lower latitudes. The rate of increased arthropod attacks per degree latitude was higher in the United States and the overall gradient was shifted poleward as compared to Brazil. PiecewiseSEM analysis revealed that aridity mediates the effect of latitude on arthropod predation and largely explains the differences in the intensity of the latitudinal gradient between study countries. Neither predator richness, predator density, nor predator resource availability predicted variation in predator attack rates. Only greater non-crop plant density drove greater predation rates, though this effect was weaker than the effect of aridity. We conclude that climatic factors rather than ecological community structure shape latitudinal arthropod predation patterns and that high levels of aridity in agroecosystems may dampen the ability of arthropod predators to provide herbivore control services as compared to natural ecosystems.

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.

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.

Frequency of Cry1F resistance alleles in Spodoptera frugiperda (Lepidoptera: Noctuidae) in Brazil.

BACKGROUND: The frequency of resistance alleles is a major factor influencing the rate of resistance evolution. Here, we adapted the F2 screen procedure for Spodoptera frugiperda (J. E. Smith) with a discriminating concentration assay, and extended associated statistical methods to estimate the frequency of resistance to Cry1F protein in S. frugiperda in Brazil when resistance was not rare. RESULTS: We show that F2 screen is efficient even when the resistance frequency is 0.250. It was possible to screen 517 isoparental lines from 12 populations sampled in five states of Brazil during the first half of 2012. Western Bahia had the highest allele frequency of Cry1F resistance, 0.192, with a 95% confidence interval (CI) between 0.163 and 0.220. All other states had a similar and lower frequency varying from 0.042 in Paraná to 0.080 in Mato Grosso do Sul. CONCLUSION: The high frequency in western Bahia may be related to year-round availability of maize, the high population density of S. frugiperda, the lack of refuges and the high adoption rate of Cry1F maize. Cry1F resistance alleles were not rare and occurred at frequencies that have already compromised the useful life of TC1507 maize in western Bahia. © 2016 Society of Chemical Industry.

Near-Isogenic Cry1F-Resistant Strain of Spodoptera frugiperda (Lepidoptera: Noctuidae) to Investigate Fitness Cost Associated With Resistance in Brazil.

Field-evolved resistance to Cry1F maize in Spodoptera frugiperda (J.E. Smith) populations in Brazil was reported in 2014. In this study, to investigate fitness costs, we constructed a near-isogenic S. frugiperda-resistant strain (R-Cry1F) using Cry1F-resistant and Cry1F-susceptible strains sharing a close genetic background. A near-isogenic R-Cry1F strain was obtained by eight repeated backcrossings, each followed by sib-mating and selection among resistant and susceptible strains. Fitness cost parameters were evaluated by comparing the biological performance of resistant, susceptible, and heterozygous strains on artificial diet. Fitness parameters monitored included development time and survival rates of egg, larval, pupal, and egg-to-adult periods; sex ratio; adult longevity; timing of preoviposition, oviposition, and postoviposition; fecundity; and fertility. A fertility life table was also calculated. The near-isogenic R-Cry1F strain showed lower survival rate of eggs (32%), when compared with Sus and reciprocal crosses (41 and 55%, respectively). The number of R-Cry1F insects that completed the life cycle was reduced to ∼25%, compared with the Sus strain with ∼32% reaching the adult stage. The mean generation time (T) of R-Cry1F strain was ∼2 d shorter than R-Cry1F♂×Sus♀ and Sus strains. The reproductive parameters of R-Cry1F strain were similar to the Sus strain. However, fewer females were produced by R-Cry1F strain than R-Cry1F♀×Sus♂ and more females than R-Cry1F♂×Sus♀. In summary, no relevant fitness costs are observed in a near-isogenic Cry1F-resistant strain of S. frugiperda, indicating stability of resistance to Cry1F protein in Brazilian populations of this species in the absence of selection pressure.

Dominance of Cry1F resistance in Spodoptera frugiperda (Lepidoptera: Noctuidae) on TC1507 Bt maize in Brazil.

BACKGROUND: Dominance of resistance has been one of the major parameters affecting the rate of evolution of resistance to Bt crops. High dose is the capacity of Bt crops to kill heterozygous insects and has been an essential component of the most successful strategy to manage resistance to these crops. Experiments were conducted to evaluate directly and indirectly whether the TC1507 event is high dose to Spodoptera frugiperda (JE Smith). RESULTS: About 8% of heterozygote neonate larvae were able to survive, complete larval development and emerge as normal adults on TC1507 leaves, while susceptible larvae could not survive for 5 days. The estimated dominance of resistance was 0.15 ± 0.09 and significantly higher than zero; therefore, the resistance to Cry1F expressed in TC1507 was not completely recessive. A 25-fold dilution of TC1507 maize leaf tissue in an artificial diet was able to cause a maximum mortality of only 37%, with growth inhibition of 82% at 7 days after larval infestation. CONCLUSION: Resistance to Cry1F in TC1507 maize is incompletely recessive in S. frugiperda. TC1507 maize is not high dose for S. frugiperda. Additional or alternative resistance management strategies, such as the replacement of single-trait Bt maize with pyramided Bt maize, which produces multiple proteins targeting the same insect pests, should be implemented wherever this technology is in use and S. frugiperda is the major pest.

Geographical and Temporal Variability in Susceptibility to Cry1F Toxin From Bacillus thuringiensis in Spodoptera frugiperda (Lepidoptera: Noctuidae) Populations in Brazil.

The genetically modified maize TC1507 event with the cry1F gene (Cry1F maize) has been used to control Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) in Brazil since the 2009-2010 cropping season. As part of the insect resistance management program, we conducted studies to determine the baseline susceptibility to Cry1F before the widespread planting of Cry1F maize. Subsequently, we evaluated the geographical and temporal variability of susceptibility to this toxin in populations of S. frugiperda collected from major maize-growing regions in Brazil. The baseline susceptibility to Cry1F was determined using a diet-overlay bioassay for a susceptible reference population and four field populations of S. frugiperda. We then monitored the susceptibility to Cry1F in 43 populations of S. frugiperda sampled in nine States of Brazil between 2011 and 2013. In the baseline study, the MIC50 (the concentration that inhibits molting to second instars in 50% of individuals) ranged from 3.59 to 72.47 ng Cry1F toxin per centimeter square. Based on the upper limit of the MIC99 value of the joint analysis from the baseline susceptibility data, the concentrations of 200 and 2,000 ng of Cry1F toxin per centimeter square were defined as diagnostic concentrations for potentially resistant individuals, and these were used to monitor the susceptibility of S. frugiperda to Cry1F. Survival at 2,000 ng Cry1F toxin per centimeter square increased significantly throughout the cropping seasons in S. frugiperda populations from São Paulo, Santa Catarina, Rio Grande do Sul, Bahia, Mato Grosso, Goiás, Mato Grosso do Sul, and Paraná. The highest survival (>50%) was reached in populations collected from Bahia, Mato Grosso, Goiás, Mato Grosso do Sul, and Paraná during the 2012-2013 cropping season. Therefore, a significant decrease in susceptibility to Cry1F was detected in S. frugiperda throughout cropping seasons, especially in regions with intensive maize production in Brazil, according to field-evolved resistance that has been demonstrated in Brazilian populations.

Managing the sugarcane borer, Diatraea saccharalis, and corn earworm, Helicoverpa zea, using Bt corn and insecticide treatments.

The sugarcane borer, Diatraea saccharalis (Fabricius) (Lepidoptera: Crambidae) and the corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), are important pests of corn in Brazil and have not been successfully managed, because of the difficulty of managing them with pesticides. The objective of this study was to evaluate the effect of Bt corn MON810, transformed with a gene from Bacillus thuringiensis Berliner (Bacillales: Bacillaceae) insecticide seed treatment, and foliar insecticide spray using treatments developed for control of the fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), which is the major pest of corn. The experiments were done under field conditions in early- and late-planted corn in the state of Rio Grande do Sul, Brazil, and in the laboratory. The MON810 corn reduced infestations and damage by D. saccharalis and H. zea. The insecticides used in seed treatments or foliar sprays did not affect D. saccharalis and H. zea infestations or damage levels. The exception was the insecticide seed treatment in non-transformed corn, which reduced early infestations of D. saccharalis. The MON810 corn, therefore, can be used for managing these two pest species, especially D. saccharalis.

[Host weeds of Rhopalosiphum rufiabdominalis (Sasaki) (Hemiptera: Aphididae) in areas of irrigated rice]. / Plantas infestantes hospedeiras de Rhopalosiphum rufiabdominalis (Sasaki) (Hemiptera: Aphididae) em áreas de cultivo de arroz irrigado.

Rhopalosiphum rufiabdominalis (Sasaki) is an insect of world-wide distribution that damages irrigated rice. From September, 2004 to February, 2005, nymphs and adults of this aphid were collected in several host weeds of rice farms in Alegrete, Quaraí and Uruguaiana, located in Western of State of Rio Grande do Sul, and Restinga Seca, in Central region of this State, Brazil. The insect was found in the root of Andropogon bicornis (West Indian foxtail), Echinochloa colona (jungle rice), Oryza sativa (volunteer rice and red-rice), Paspalum sp. (paspalum) and Soliva pterosperma (lawn burweed).

Plantas infestantes hospedeiras de Rhopalosiphum rufiabdominalis (Sasaki) (Hemiptera: Aphididae) em áreas de cultivo de arroz irrigado / Host weeds of Rhopalosiphum rufiabdominalis (Sasaki) (Hemiptera: Aphididae) in areas of irrigated rice

Rhopalosiphum rufiabdominalis (Sasaki) é um inseto que causa dano à cultura do arroz-irrigado e tem ampla distribuição pelo mundo. Durante o período de setembro de 2004 a fevereiro de 2005, foram coletados ninfas e adultos desse afídeo em diversas plantas daninhas presentes em lavouras arrozeiras nos municípios de Alegrete, Quaraí e Uruguaiana, na região da fronteira oeste do Rio Grande do Sul, e Restinga Seca, na Região Central do Estado. O inseto foi encontrado nas raízes de Andropogon bicornis (capim-rabo-de-burro), Echinochloa colona (capim-arroz), arroz espontâneo e Oryza sativa (arroz-vermelho), Paspalum sp. (paspalum) e Soliva pterosperma (roseta).

Rhopalosiphum rufiabdominalis (Sasaki) is an insect of world-wide distribution that damages irrigated rice. From September, 2004 to February, 2005, nymphs and adults of this aphid were collected in several host weeds of rice farms in Alegrete, Quaraí and Uruguaiana, located in Western of State of Rio Grande do Sul, and Restinga Seca, in Central region of this State, Brazil. The insect was found in the root of Andropogon bicornis (West Indian foxtail), Echinochloa colona (jungle rice), Oryza sativa (volunteer rice and red-rice), Paspalum sp. (paspalum) and Soliva pterosperma (lawn burweed).