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Spodoptera frugiperda (J.E. Smith) is one of the key cross-crop pests in Brazilian agroecosystems. Field-evolved resistance of S. frugiperda to some conventional insecticides and Bt proteins has already been reported. Thus, the use of insecticides with new mode of action such as sodium channel blockers (indoxacarb and metaflumizone) could be an important tool in insecticide resistance management (IRM) programs. To implement a proactive IRM, we conducted baseline response and monitoring to indoxacarb and metaflumizone in 87 field populations of S. frugiperda collected from major maize-growing regions of Brazil from 2017 to 2020, estimated the frequency of resistance alleles to indoxacarb, and evaluated cross-resistance of indoxacarb and metaflumizone to some selected insecticides and Bt proteins. Low variation in susceptibility to indoxacarb (4.6-fold) and metaflumizone (2.6-fold) was detected in populations of S. frugiperda in 2017. The frequency of the resistance allele to indoxacarb was 0.0452 (0.0382-0.0527 CI 95%), by using F2 screen method. The mean survival at diagnostic concentration, based on CL99, varied from 0.2 to 12.2% for indoxacarb and from 0.0 to 12.7% for metaflumizone, confirming high susceptibility of S. frugiperda to these insecticides in Brazil. No cross-resistance was detected between sodium channel blocker insecticides and other insecticides (organophosphate, pyrethroid, benzoylurea, spinosyn, and diamide) and Bt proteins. These findings showed that sodium channel blocker insecticides are important candidates to be exploited in IRM strategies of S. frugiperda in Brazil.

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ABSTRACT Leaf-cutting ants are controlled with toxic baits. For the method's greater efficiency, the baits must be distributed and processed by workers during fungus cultivation. To test hypotheses whether the mode of action of the active ingredients, which blocks the sodium channels and interrupts the production of ATP in the mitochondria, interferes with fragment distribution in nests; the dispersion of pellets fragments during fungus cultivation by workers was assessed, spatially referencing the fragment onto the fungus garden. Pellets fragments were randomly distributed, but the amount pellets fragments was influenced by the way that the active ingredient acts in the colony.

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Abstract Diamondback moth (DBM), Plutella xylostella (Linnaeus), is a notorious pest of brassica crops worldwide and is resistant to all groups of insecticides. The insect system harbors diverse groups of microbiota, which in turn helps in enzymatic degradation of xenobiotic-like insecticides. The present study aimed to determine the diversity of gut microflora in DBM, quantify esterase activity and elucidate their possible role in degradation of indoxacarb. We screened 11 geographic populations of DBM in India and analyzed them for bacterial diversity. The culturable gut bacterial flora underwent molecular characterization with 16S rRNA. We obtained 25 bacterial isolates from larvae (n = 13) and adults (n = 12) of DBM. In larval gut isolates, gammaproteobacteria was the most abundant (76%), followed by bacilli (15.4%). Molecular characterization placed adult gut bacterial strains into three major classes based on abundance: gammaproteobacteria (66%), bacilli (16.7%) and flavobacteria (16.7%). Esterase activity from 19 gut bacterial isolates ranged from 0.072 to 2.32 µmol/min/mg protein. Esterase bands were observed in 15 bacterial strains and the banding pattern differed in Bacillus cereus – KC985225 and Pantoea agglomerans – KC985229. The bands were characterized as carboxylesterase with profenofos used as an inhibitor. Minimal media study showed that B. cereus degraded indoxacarb up to 20%, so it could use indoxacarb for metabolism and growth. Furthermore, esterase activity was greater with minimal media than control media: 1.87 versus 0.26 µmol/min/mg protein. Apart from the insect esterases, bacterial carboxylesterase may aid in the degradation of insecticides in DBM.

Assuntos

RESUMO

Diamondback moth (DBM), Plutella xylostella (Linnaeus), is a notorious pest of brassica crops worldwide and is resistant to all groups of insecticides. The insect system harbors diverse groups of microbiota, which in turn helps in enzymatic degradation of xenobiotic-like insecticides. The present study aimed to determine the diversity of gut microflora in DBM, quantify esterase activity and elucidate their possible role in degradation of indoxacarb. We screened 11 geographic populations of DBM in India and analyzed them for bacterial diversity. The culturable gut bacterial flora underwent molecular characterization with 16S rRNA. We obtained 25 bacterial isolates from larvae (n = 13) and adults (n = 12) of DBM. In larval gut isolates, gammaproteobacteria was the most abundant (76%), followed by bacilli (15.4%). Molecular characterization placed adult gut bacterial strains into three major classes based on abundance: gammaproteobacteria (66%), bacilli (16.7%) and flavobacteria (16.7%). Esterase activity from 19 gut bacterial isolates ranged from 0.072 to 2.32 µmol/min/mg protein. Esterase bands were observed in 15 bacterial strains and the banding pattern differed in Bacillus cereus KC985225 and Pantoea agglomerans KC985229. The bands were characterized as carboxylesterase with profenofos used as an inhibitor. Minimal media study showed that B. cereus degraded indoxacarb up to 20%, so it could use indoxacarb for metabolism and growth. Furthermore, esterase activity was greater with minimal media than control media: 1.87 versus 0.26 µmol/min/mg protein. Apart from the insect esterases, bacterial carboxylesterase may aid in the degradation of insecticides in DBM.(AU)

Assuntos

RESUMO

Diamondback moth (DBM), Plutella xylostella (Linnaeus), is a notorious pest of brassica crops worldwide and is resistant to all groups of insecticides. The insect system harbors diverse groups of microbiota, which in turn helps in enzymatic degradation of xenobiotic-like insecticides. The present study aimed to determine the diversity of gut microflora in DBM, quantify esterase activity and elucidate their possible role in degradation of indoxacarb. We screened 11 geographic populations of DBM in India and analyzed them for bacterial diversity. The culturable gut bacterial flora underwent molecular characterization with 16S rRNA. We obtained 25 bacterial isolates from larvae (n=13) and adults (n=12) of DBM. In larval gut isolates, gammaproteobacteria was the most abundant (76%), followed by bacilli (15.4%). Molecular characterization placed adult gut bacterial strains into three major classes based on abundance: gammaproteobacteria (66%), bacilli (16.7%) and flavobacteria (16.7%). Esterase activity from 19 gut bacterial isolates ranged from 0.072 to 2.32µmol/min/mg protein. Esterase bands were observed in 15 bacterial strains and the banding pattern differed in Bacillus cereus - KC985225 and Pantoea agglomerans - KC985229. The bands were characterized as carboxylesterase with profenofos used as an inhibitor. Minimal media study showed that B. cereus degraded indoxacarb up to 20%, so it could use indoxacarb for metabolism and growth. Furthermore, esterase activity was greater with minimal media than control media: 1.87 versus 0.26µmol/min/mg protein. Apart from the insect esterases, bacterial carboxylesterase may aid in the degradation of insecticides in DBM.

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Background: Pesticides are substances used for pest control. Due to their persistence in the environment, they can induce toxicity in humans and animals. Indoxacarb is an oxadiazine insecticide that acts against insects of the order Lepidoptera. Choice of rats and cats used in this study is based on factors such as these animals have a high count of micronucleated polychromatic erythrocytes and the product is intended for use in cats. Limited data in literature pertaining to the mutagenic effects of this product motivated this study. The aim of this study was to evaluate the effect of the micronucleus test on the mutagenicity of indoxacarb when administered in one and tenfold therapeutic doses in rats and cats.Materials, Methods & Results: Forty male Wistar rats aged 70 days and weighing 280 ± 10 g and 20 mixed breed male and female adult cats weighing 4 ± 0.2 kg were selected. These animals were obtained from the central animal facility and cattery, respectively, of the university of origin. Rats were reared in individual cages with a controlled temperature of 22°C ± 2°C, humidity of 55% ± 5% and 12-h light–dark cycle. Cats were reared in individual stalls with water and food ad libitum. Animals were randomly distributed into four groups comprising 10 rats and 5 cats in respective groups: negative control group, which received 0.9% sodium chloride solution as a single topical administration; positive control group, which received 50 mg/kg cyclophosphamide as a single intra-peritoneal (rats) or intravenous injection (cats); indoxacarb group, which received indoxacarb as a single topical dose according to the manufacturer’s recommendations; and high dose indoxacarb group, which also received indoxacarb in a single topical dose, but at a tenfold concentration. Rats were evaluated 24 h after indoxacarb administration. After euthanasia, rat femurs were obtained and their medullary canals were washed using fetal bovine serum.[...]

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Background: Pesticides are substances used for pest control. Due to their persistence in the environment, they can induce toxicity in humans and animals. Indoxacarb is an oxadiazine insecticide that acts against insects of the order Lepidoptera. Choice of rats and cats used in this study is based on factors such as these animals have a high count of micronucleated polychromatic erythrocytes and the product is intended for use in cats. Limited data in literature pertaining to the mutagenic effects of this product motivated this study. The aim of this study was to evaluate the effect of the micronucleus test on the mutagenicity of indoxacarb when administered in one and tenfold therapeutic doses in rats and cats.Materials, Methods & Results: Forty male Wistar rats aged 70 days and weighing 280 ± 10 g and 20 mixed breed male and female adult cats weighing 4 ± 0.2 kg were selected. These animals were obtained from the central animal facility and cattery, respectively, of the university of origin. Rats were reared in individual cages with a controlled temperature of 22°C ± 2°C, humidity of 55% ± 5% and 12-h light–dark cycle. Cats were reared in individual stalls with water and food ad libitum. Animals were randomly distributed into four groups comprising 10 rats and 5 cats in respective groups: negative control group, which received 0.9% sodium chloride solution as a single topical administration; positive control group, which received 50 mg/kg cyclophosphamide as a single intra-peritoneal (rats) or intravenous injection (cats); indoxacarb group, which received indoxacarb as a single topical dose according to the manufacturers recommendations; and high dose indoxacarb group, which also received indoxacarb in a single topical dose, but at a tenfold concentration. Rats were evaluated 24 h after indoxacarb administration. After euthanasia, rat femurs were obtained and their medullary canals were washed using fetal bovine serum.[...](AU)

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