The rise of large scale agriculture in the 20th century created the need for effective strategies to control insect pests. Treatment with chemical insecticides has been a weapon of choice, but the inevitable evolution of resistance has followed in many insect species. Resistance represents a major challenge, not only for agricultural production, but also for environmental preservation and human health. Two major options for resistance have been identified, and these are target-site based and metabolic-based resistance. Much insecticide resistance research focuses on identifying these mechanisms through genetic and molecular analysis. The insecticide lufenuron is the focus of this study. It belongs to a novel insecticidal group called the insect growth regulators, which were introduced in 1970s as highly selective insecticides with low vertebrate toxicity. Resistance to lufenuron in the non-pest species Drosophila melanogaster has been observed in field populations, despite the lack of field usage of lufenuron (Wilson & Cain, 1997; O’Keefe, 1997). This study has taken advantage of this phenomenon to investigate resistance mechanisms in natural populations. At least two detoxification mechanisms were identified. (For complete abstract open document)

Os reguladores de crescimento de insetos têm sido um dos mais importantes grupos de inseticidas recomendados para o controle de Helicoverpa armigera (Hübner) e Spodoptera frugiperda (J. E. Smith) no Brasil, que são consideradas pragas-chave de vários sistemas de produção agrícola. Para implementar programas de manejo da resistência de insetos, o presente trabalho teve como objetivo caracterizar a suscetibilidade a inseticidas reguladores de crescimento de insetos em populações de H. armigera e S. frugiperda do Brasil. A caracterização das linhas-básica de suscetibilidade de H. armigera a lufenuron e methoxifenozide e de S. frugiperda a methoxifenozide foi realizada com bioensaio de tratamento superficial da dieta artificial com inseticida, utilizando-se lagartas de 3º instar. Foram verificadas baixa variabilidade na suscetibilidade de H. armigera a lufenuron, com DL50 variando de 0,30 a 1,02 &mu;g de i.a./cm2 de dieta, e a methoxifenozide, com DL50 de 2,61 a 8,02 &mu;g de i.a./cm2 de dieta, em populações coletadas em diferentes regiões agrícolas na safra 2013/2014. As doses diagnósticas, baseadas na DL99, foram de 6,36 &mu;g de i.a/cm2 de dieta para lufenuron e 31,10 &mu;g de i.a/cm2 de dieta para methoxifenozide. Foram observadas variações geográfica e temporal na suscetibilidade a lufenuron e methoxifenozide em populações de H. armigera coletadas nas safras de 2013/2014 a 2016/2017; contudo, não foi possível isolar linhagens de H. armigera resistentes a estes inseticidas, mediante o uso de técnicas de \"F2 screen\" e seleção massal. Uma baixa variabilidade na suscetibilidade de S. frugiperda a methoxifenozide foi observada para as populações coletadas na segunda safra de 2016, com DL50 variando de 0,5 a 2,1 &mu;g de i.a/cm2 de dieta. A dose diagnóstica (DL99) para monitoramento da suscetibilidade a methoxifenozide em populações de S. frugiperda foi de 6 &mu;g de i.a/cm2 de dieta. Na 2ª safra de 2016, a sobrevivência das populações de S. frugiperda avaliadas foram baixas, com valores inferiores a 10% na dose diagnóstica. Por outro lado, na 1ª safra de 2017, houve aumento na sobrevivência das populações testadas, atingindo valores de até 62%. A linhagem de S. frugiperda resistente a methoxifenozide selecionada em condições de laboratório apresentou uma baixa razão de resistência (&asymp;5 vezes). Os resultados da presente pesquisa confirmaram a alta suscetibilidade de H. armigera a lufenuron e methoxifenozide e de S. frugiperda a methoxyfenozide. As informações obtidas no presente estudo servirão para a implementação de programas proativos de manejo da resistência a esses inseticidas. / Insect growth regulators have been one of the most important group of insecticides recommended for controlling Helicoverpa armigera (Hübner) and Spodoptera frugiperda (J. E. Smith) in Brazil which are considered key pests of several crop production systems. To implement insect resistance management programs, the objective of this research was to characterize the susceptibility to insect growth regulators in H. armigera and S. frugiperda populations from Brazil. Baseline susceptibilities of H. armigera to lufenuron and methoxifenozide and S. frugiperda to methoxifenozide were conducted with artificial diet overlay bioassays using 3rd instar larvae. There was low variability in the susceptibility of H. armigera to lufenuron, with LD50 ranging from 0.30 to 1.02 &mu;g of a.i./cm2 of diet, and to methoxifenozide, with LD50 of 2.61 to 8.02 &mu;g of a.i./cm2 of diet across populations collected in different agricultural regions in 2013/2014 growing season. The diagnostic doses, based on DL99, were 6.36 &mu;g of a.i./cm2 of diet for lufenuron and 31.10 &mu;g of a.i./cm2 of diet for methoxifenozide. Geographic and temporal variations in susceptibility to lufenuron and methoxifenozide were observed in populations of H. armigera collected from 2013/2014 to 2016/2017 growing seasons; however, it was not possible to isolate resistant strains to these insecticides using F2 screen and massal selection approaches. There was also a low variability in the susceptibility of S. frugiperda to methoxifenozide across populations collected in the 2nd crop season in 2016, with LD50 ranging from 0.5 to 2.1 &mu;g of a.i./cm2 of diet. The diagnostic dose (DL99) for monitoring the susceptibility to methoxifenozide in S. frugiperda populations was 6 &mu;g of a.i./cm2 of diet. In the 2nd crop season of 2016, the survival at diagnostic dose of S. frugiperda populations evaluated was low (< 10%). On the other hand, in the 1st crop season of 2017, there was a significant increase in the survival across the populations tested, with values reaching up to 62% at diagnostic dose. The laboratory-selected resistant strain of S. frugiperda to methoxifenozide showed a low resistance ratio (&asymp;5 times). We confirmed the high susceptibility of H. armigera to lufenuron and methoxifenozide and S. frugiperda to methoxifenozide in Brazil. The information collected in this study will be important for implementing a proactive resistance management programs to these insecticides.

Os reguladores de crescimento de insetos têm sido um dos mais importantes grupos de inseticidas recomendados para o controle de Helicoverpa armigera (Hübner) e Spodoptera frugiperda (J. E. Smith) no Brasil, que são consideradas pragas-chave de vários sistemas de produção agrícola. Para implementar programas de manejo da resistência de insetos, o presente trabalho teve como objetivo caracterizar a suscetibilidade a inseticidas reguladores de crescimento de insetos em populações de H. armigera e S. frugiperda do Brasil. A caracterização das linhas-básica de suscetibilidade de H. armigera a lufenuron e methoxifenozide e de S. frugiperda a methoxifenozide foi realizada com bioensaio de tratamento superficial da dieta artificial com inseticida, utilizando-se lagartas de 3º instar. Foram verificadas baixa variabilidade na suscetibilidade de H. armigera a lufenuron, com DL50 variando de 0,30 a 1,02 &mu;g de i.a./cm2 de dieta, e a methoxifenozide, com DL50 de 2,61 a 8,02 &mu;g de i.a./cm2 de dieta, em populações coletadas em diferentes regiões agrícolas na safra 2013/2014. As doses diagnósticas, baseadas na DL99, foram de 6,36 &mu;g de i.a/cm2 de dieta para lufenuron e 31,10 &mu;g de i.a/cm2 de dieta para methoxifenozide. Foram observadas variações geográfica e temporal na suscetibilidade a lufenuron e methoxifenozide em populações de H. armigera coletadas nas safras de 2013/2014 a 2016/2017; contudo, não foi possível isolar linhagens de H. armigera resistentes a estes inseticidas, mediante o uso de técnicas de \"F2 screen\" e seleção massal. Uma baixa variabilidade na suscetibilidade de S. frugiperda a methoxifenozide foi observada para as populações coletadas na segunda safra de 2016, com DL50 variando de 0,5 a 2,1 &mu;g de i.a/cm2 de dieta. A dose diagnóstica (DL99) para monitoramento da suscetibilidade a methoxifenozide em populações de S. frugiperda foi de 6 &mu;g de i.a/cm2 de dieta. Na 2ª safra de 2016, a sobrevivência das populações de S. frugiperda avaliadas foram baixas, com valores inferiores a 10% na dose diagnóstica. Por outro lado, na 1ª safra de 2017, houve aumento na sobrevivência das populações testadas, atingindo valores de até 62%. A linhagem de S. frugiperda resistente a methoxifenozide selecionada em condições de laboratório apresentou uma baixa razão de resistência (&asymp;5 vezes). Os resultados da presente pesquisa confirmaram a alta suscetibilidade de H. armigera a lufenuron e methoxifenozide e de S. frugiperda a methoxyfenozide. As informações obtidas no presente estudo servirão para a implementação de programas proativos de manejo da resistência a esses inseticidas. / Insect growth regulators have been one of the most important group of insecticides recommended for controlling Helicoverpa armigera (Hübner) and Spodoptera frugiperda (J. E. Smith) in Brazil which are considered key pests of several crop production systems. To implement insect resistance management programs, the objective of this research was to characterize the susceptibility to insect growth regulators in H. armigera and S. frugiperda populations from Brazil. Baseline susceptibilities of H. armigera to lufenuron and methoxifenozide and S. frugiperda to methoxifenozide were conducted with artificial diet overlay bioassays using 3rd instar larvae. There was low variability in the susceptibility of H. armigera to lufenuron, with LD50 ranging from 0.30 to 1.02 &mu;g of a.i./cm2 of diet, and to methoxifenozide, with LD50 of 2.61 to 8.02 &mu;g of a.i./cm2 of diet across populations collected in different agricultural regions in 2013/2014 growing season. The diagnostic doses, based on DL99, were 6.36 &mu;g of a.i./cm2 of diet for lufenuron and 31.10 &mu;g of a.i./cm2 of diet for methoxifenozide. Geographic and temporal variations in susceptibility to lufenuron and methoxifenozide were observed in populations of H. armigera collected from 2013/2014 to 2016/2017 growing seasons; however, it was not possible to isolate resistant strains to these insecticides using F2 screen and massal selection approaches. There was also a low variability in the susceptibility of S. frugiperda to methoxifenozide across populations collected in the 2nd crop season in 2016, with LD50 ranging from 0.5 to 2.1 &mu;g of a.i./cm2 of diet. The diagnostic dose (DL99) for monitoring the susceptibility to methoxifenozide in S. frugiperda populations was 6 &mu;g of a.i./cm2 of diet. In the 2nd crop season of 2016, the survival at diagnostic dose of S. frugiperda populations evaluated was low (< 10%). On the other hand, in the 1st crop season of 2017, there was a significant increase in the survival across the populations tested, with values reaching up to 62% at diagnostic dose. The laboratory-selected resistant strain of S. frugiperda to methoxifenozide showed a low resistance ratio (&asymp;5 times). We confirmed the high susceptibility of H. armigera to lufenuron and methoxifenozide and S. frugiperda to methoxifenozide in Brazil. The information collected in this study will be important for implementing a proactive resistance management programs to these insecticides.

El lufenuron un insecticida del grupo de los benzilureas, el cual interfiere con la síntesis de la quitina que causa una inhibición en la muda de los insectos. Se evaluó el efecto tóxico del lufenuron sobre seis organismos bioindicadores de calidad ambiental. Se desarrollaron los bioensayos con el lufenuron sobre seis organismos bioindicadores de calidad ambiental: Chlorella vulgaris (Beijerinck, 1890), Artemia franciscana (Kellogg, 1906), Daphnia magna (Straus, 1820), Carassius auratus (Linnaeus, 1758), Microorganismos de Suelo y Eisenia foetida (Savigny, 1826). Se utilizó el análisis de varianza (ANDEVA) con prueba de Tukey y con el Probit se calcularon los parámetros ecotoxicológicos. Los resultados son los siguientes, C. vulgaris (CI50<2,46 mg i.a.·L-1 a 96 h), A. franciscana (CL50= 11,41 μg i.a.·L-1 a 48 h), D. magna (CL50= 0,05 μg i.a.·L-1 a 48h), D. magna (NOEC= 0,00005 mg i.a.·L-1 / LOEC= 0,0001 mg i.a.·L-1 para el numero de crías vivas a 21 d), C. auratus (NOEC= 0, 061 mg i.a.·L-1/ LOEC= 0.122 mg i.a.·L-1 para el porcentaje de mortalidad acumulada a 26 d), Microorganismos de Suelo (NOEC= 1820 mg i.a.·g-1 / LOEC> 1820 mg i.a.·g-1) y E. foetida (DL50= 206,31 mg i.a.·Kg-1 a 14 d ; NOEC< 21,2 mg i.a.·Kg-1 / LOEC= 21,2 mg i.a.·Kg-1 a 14 d). Se observó la siguiente secuencia de ecotoxicidad decreciente mediado por los efectos letales y subletales producidos durante los bioensayos con los seis organismos: D. magna > A. franciscana > C. vulgaris > C. auratus > E. foetida > Microorganismos del suelo. Daphnia magna fue el organismo bioindicador más sensible al lufenuron y el más resistente fueron los microorganismos del suelo. El lufenuron presentó mayores porcentajes de mortalidad e inhibición en los organismos acuáticos que en los terrestres. Se concluyó que los seis organismos escogidos para evaluar los posibles daños ambientales del insecticida lufenuron, ayudaron a clarificar que este compuesto daña principalmente la cadena trófica acuática que la terrestre, siendo más sensibles los ecosistemas acuáticos que los terrestres que presentan riesgo bajo.Lufenuron is an insecticide from the group of benzylureas, which interferes with the synthesis of chitin causing inhibition of insect moulting. The toxic effect of lufenuron on six environmental quality bioindicator organisms was evaluated. Bioassays with lufenuron were developed on six environmental quality bioindicators: Chlorella vulgaris (Beijerinck, 1890), Artemia franciscana (Kellogg, 1906), Daphnia magna (Straus, 1820), Carassius auratus (Linnaeus, 1758) and Eisenia foetida (Savigny, 1826). The analysis of variance (ANDEVA) was used with Tukey's test and with the Probit we calculated the ecotoxicological parameters. The results are as follows: C. vulgaris (IC50 <2,46 mg i.a.·L-1 at 96 h), A. franciscana (LC50 = 11,41 μg i.a.·L-1 at 48 h), D. magna LC50 = 0,05 μg i.a.·L-1 at 48 h), D. magna (NOEC = 0,00005 mg i.a.·L-1 / LOEC = 0,0001 mg i.a.·L-1 for the number of live offspring at 21 d), C. auratus (NOEC = 0,061 mg i.a.·L-1 / LOEC = 0.122 mg i.a.·L-1 for the percentage of accumulated Mortality at 26 d), Soil Microorganisms (NOEC = 1820 mg i.a.·g-1/ LOEC> 1820 mg i.a.·g-1) and E. foetida (LD50 = 206,31 mg i.a.·kg-1 at 14 d; NOEC <21,2 mg i.a.·kg-1 / LOEC = 21,2 mg i.a.·kg-1 at 14 d). The following sequence of decreasing ecotoxicity mediated by the lethal and sublethal effects produced during the bioassays with the six organisms was observed: D. magna> A. franciscana> C. vulgaris> C. auratus> E. foetida> Soil microorganisms. Daphnia magna was the most bioindicator organism of lufenuron, and the most resistant soil microorganisms. Lufenuron had higher rates of mortality and inhibition in aquatic organisms than in terrestrial organisms. It was concluded that the six organisms chosen to evaluate the possible environmental damages of the insecticide lufenuron, helped to clarify that this compound damages mainly the trophic chain aquatic that the terrestrial chain, being more sensitive aquatic ecosystems that the terrestrial ones.