BACKGROUND Understanding the genetic basis of insect resistance to insecticides can help to implement insecticide resistance management (IRM) strategies. In this study, we selected a strain of Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) resistant to chlorantraniliprole using the F2 screen method, characterized the inheritance of resistance and evaluated patterns of cross‐resistance to other diamide insecticides. RESULTS The chlorantraniliprole‐resistant strain (Chlorant‐R) was selected from a field‐collected population with an estimated allele frequency of 0.1316. The estimated median lethal concentration (LC50) values were 0.011 and 2.610 µg a.i. cm–2 for the susceptible (Sus) and Chlorant‐R strains, respectively, resulting in a resistance ratio (RR) of 237‐fold. The LC50 values of the reciprocal crosses were 0.155 and 0.164 µg a.i. cm–2, indicating that resistance is autosomally inherited. Resistance was characterized as incompletely recessive and monogenic at concentrations close to the recommended field rates of chlorantraniliprole. Survival of the resistant strain and heterozygous larvae in maize plants treated at the field rate was ∼ 60 (similar to the susceptible strain on untreated maize) and 15%, respectively. The Chlorant‐R strain showed low cross‐resistance to cyantraniliprole (RR ∼ 27‐fold) and very high cross‐resistance to flubendiamide (RR > 42 000‐fold). CONCLUSIONS The frequency of chlorantraniliprole resistance allele was moderately high in a field‐collected population of S. frugiperda. The inheritance of chlorantraniliprole resistance was characterized as autosomal, incompletely recessive and monogenic. S. frugiperda showed cross‐resistance to other diamide insecticides. These results provide essential information for the implementation of IRM programs to preserve the useful life of diamide insecticides for controlling S. frugiperda in Brazil. © 2019 Society of Chemical Industry

BACKGROUNDThe use of spinosyn insecticides is one of the major control strategies of the fall armyworm, Spodoptera frugiperda (J. E. Smith) in Brazil. In this study, we selected a spinetoram‐resistant strain from a field‐population of S. frugiperda to characterize the inheritance of the resistance and cross‐resistance relationship between spinosyn insecticides.RESULTSThe values of LC50 (95% CI) obtained from concentration–response bioassays were 0.63 (0.55–0.73) μg spinetoram mL−1 for the susceptible strain (SUS), and 1170.96 (1041.61–1323.89) μg spinetoram mL−1 for the strain resistant to spinetoram (SPT‐R). These values resulted in a resistance ratio of 1844‐fold. The SPT‐R strain showed cross‐resistance with spinosad (resistance ratio = 1196‐fold). The reciprocal crosses showed LC50 values of 3.91 (2.97–5.84) and 5.37 (4.52–6.52) μg spinetoram mL−1, suggesting that the resistance of S. frugiperda to spinetoram is autosomal and incompletely recessive. The backcrosses of the F1 progeny with the SPT‐R strain suggest a resistance with polygenic effect. Estimates of the effective number of loci with equal contributions to the resistance effect were from 1.18 to 1.76, suggesting that resistance to spinetoram is associated with a few genes.CONCLUSIONThe inheritance pattern of resistance of S. frugiperda to spinetoram was characterized as autosomal, incompletely recessive and polygenic. Cross‐resistance between spinosyns was confirmed in S. frugiperda. The importance of this information for implementing insect resistance management strategies is discussed in this paper. © 2020 Society of Chemical Industry

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.

RESUMO Estudos realizados com Brassica sp. demonstram que o estresse salino afeta a qualidade fisiológica e o vigor das sementes. Assim, a busca por substâncias que minimizem os efeitos provocados pelo estresse salino durante a germinação são de grande importância. Objetivou-se com este trabalho avaliar a ação de substâncias liberadoras de óxido nítrico durante a germinação de sementes de repolho cultivado sob condições de salinidade. As sementes foram pré-embebidas em soluções de nitrato de potássio (KNO3) e nitroprus siato de sódio (SNP) nas concentrações de zero (controle), 0,01, 0,10, 1,00 e 10,00 mmol L-1, por 30 minutos. Posteriormente, distribuídas sobre papel germitest em placas de Petri, umedecido com solução salina de NaCl nos potenciais de zero, -0,6 e -1,2 MPa. Foram avaliados a germinação, primeira contagem de germinação, índice de velocidade de germinação, tempo médio de germinação, comprimento de parte aérea, comprimento de raiz e massa seca das plântulas. Não houve germinação no potencial osmótico de -1,2 MPa. O potencial de -0,6 MPa reduz a germinação e o desenvolvimento das plântulas de repolho. Os resultados sugerem que houve ação positiva do KNO3 e do SNP na concentração de 0,01 mmol L-1, revertendo o estresse provocado pela salinidade (-0,6 MPa de NaCl).

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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Resumo. O objetivo deste trabalho foi estudar a influência da temperatura sobre parametros demográficos do parasitóide de ovos, Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae), criados em ovos da lagarta falsa-medidera-das-crucíferas, Trichoplusia ni Hübner (Lepidoptera: Noctuidae), em condições de laboratório. Para tal foram confeccionadas cartelas azuis celeste contendo ovos de T. ni que foram oferecidos ao parasitismo de T. pretiosum por 24 horas nas temperaturas de 18, 21, 24, 27, 30 e 33 °C. Após esse período, os parasitóides foram retirados e as cartelas mantidas nos mesmos condicionamentos térmicos até a emergência dos descendentes. A partir da emergência dos descendentes, fêmeas de T. pretiosum foram individualizadas em tubos tipo Eppendorf sendo alimentadas com mel e mantidas nas temperaturas de origem. A duração do período ovo-adulto e a longevidade das fêmeas foram fortemente influenciadas pelo regime térmico estudado, sendo inversos ao seu aumento (16,5 a 4,5 dias, para o período ovo-adulto; e 11,9 a 5,5 dias, para longevidade das fêmeas). O percentual de emergência dos descendentes, número de descendentes por ovo e a razão de sexos não sofreram influencia estatisticamente significativa. A sobrevivência (L x ) de T. pretiosum foi mais influenciada nas temperaturas 27, 30 e 33 °C. A esperança de vida dos adultos (e x ) foi maior nas temperaturas inferiores (18, 21 e 24 °C) verificando-se, em média, expectativas de vida de 32, 28 e 26 dias, respectivamente. Desta maneira verificou-se que a temperatura pode ser o fator limitante para o desenvolvimento e sobrevivência de T. pretiosum em programas de controle biológico de T. ni.Palavras-chave: Insecta; Parasitoide de ovos; Tabela de vida; Temperatura. Table of Life Expectancy of Trichogramma pretiosum Riley in Eggs of Trichoplusia ni Hübner Different Thermal ConditioningAbstract. The objective of this work was to study the influence of temperature on demographic parameters of the egg parasitoid, Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) reared on eggs of cabbage looper, Trichoplusia ni Hübner (Lepidoptera: Noctuidae) in conditions the laboratory. To this end, we made sky blue cards containing eggs of T. ni that were offered to the parasitism of T. pretiosum for 24 hours at temperatures of 18, 21, 24, 27, 30 and 33 °C. After this period, the parasitoids were removed and kept the cards in the same thermal constraints to the emergence of offspring. From the emergence of offspring, females of T. pretiosum were individually placed in Eppendorf tubes being fed honey and kept at temperatures of origin. The duration of egg-adult period and female longevity were strongly influenced by thermal regime, being opposite to its increase (16.5 to 4.5 days, for the duration of egg-adult period; and 11.9 to 5.5 days, for and female longevity). The percentage of emergence of offspring, number of offspring per egg and sex ratio were not influenced statistically significant. The survival (L x ) of T. pretiosum was more influenced at temperatu...

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