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Simple Summary: The beet armyworm Spodoptera exigua (Hübner) is a polyphagous pest of numerous cultivated crops including potatoes, beans, asparagus, cotton, etc., causing considerable economic losses in crop production worldwide. Currently, the use of chemical insecticides is the most commonly used method to control this pest, however, the overuse of them results in insecticide resistance, environmental pollution and toxicity to other non-target organisms. Our results indicated that S. exigua field populations had developed resistance to almost half of the eleven commonly used insecticides with different modes of action. Thus, it is extremely urgent to seek an efficient strategy for insecticide resistance management. We found that the combined application of the specific entomopathogen of S. exigua (Spodoptera exigua multiple nucleopolyhedrovirus, SeMNPV) reduced insecticide resistance or even recovered the susceptibility to insecticides and enhanced the toxicity obviously in both laboratory experiments and field trials. These findings are valuable to provide a promising efficient way for improving insecticide resistance management strategy and an environmentally friendly approach for pest management with the combined application of nucleopolyhedroviruses and insecticides. Spodoptera exigua is a polyphagous pest of diverse crops and causes considerable economic losses. The overuse of chemical insecticides for controlling this pest results in insecticide resistance, environmental pollution and toxicity to other non-target organisms. Therefore, a sustainable and efficient way for pest management is urgently required. In this study, laboratory bioassays of eleven commonly used insecticides, the specific entomopathogen of S. exigua (Spodoptera exigua multiple nucleopolyhedrovirus, SeMNPV), and SeMNPV-insecticide combinations against the S. exigua laboratory population and two field populations were tested. Our results indicated that the two field populations had developed resistance to almost half of the tested insecticides, while SeMNPV had good virulence in all populations. Interestingly, the combined use of SeMNPV enhanced the toxicity of the tested insecticides against all populations to a different extent and considerably reduced the insecticide resistance of S. exigua field populations or even recovered the susceptibility to above insecticides. Furthermore, the field trial showed that the combined application of SeMNPV contributed to promoting the control efficacy of emamectin benzonate and chlorfenapyr. These results provide a promising efficient way for pest resistance management and an environmentally friendly approach for controlling S. exigua with the combined application of nucleopolyhedroviruses and insecticides. [ABSTRACT FROM AUTHOR]

Many species of devastating insect pests have acquired a high degree of resistance to insecticides in the field during the last few decades. Spodoptera exigua, for example, is the most damaging pests of economic crops with a worldwide spread. In a present study, the comparative growth, reproduction, and detoxification enzyme activity were evaluated along with exposure to three insecticides at low lethal doses of lufenuron, indoxacarb, and spinosad as compared to the control. Results indicate that the larval developmental time was significantly extended on lufenuron (21.5 ± 29 days) followed by indoxacarb (20.28 ± 0.24 days) and spinosad (19.74 ± 0.23 days) as compared to that on the control (18.13 ± 0.13 days). Similarly, the lowest number of eggs of S. exigua females were recorded on lufenuron (328.75 ± 50.81 eggs) followed by spinosad (367 ± 36.4 eggs) and indoxacarb (411.58 ± 42.38 eggs) as compared to that on the control (560.2 ± 13.47). Interestingly, the lowest intrinsic rate of increase (r) (0.121 ± 0.009) and highest mean generation time (T) (36.2 ± 0.35 days) were observed when larvae were treated to a low lethal concentration (LC20) of lufenuron as compared to that of indoxacarb, spinosad, and control. In addition, considerably lower activity of all detoxification enzymes in larvae was recorded on lufenuron after control as compared to that on indoxacarb and spinosad. Our study serves as a reference and basis for the toxicity and low lethal evaluation of lufenuron, indoxacarb, and spinosad on life table parameters and enzymatic properties in S. exigua, which may contribute to identifying targets for effective control of S. exigua. [ABSTRACT FROM AUTHOR]

The beet armyworm (Spodoptera exigua) is a highly polyphagous agricultural pest that is distributed worldwide. However, the adaptive mechanisms of S. exigua for various insecticides and defensive substances in host plants are unknown. Insect P450 monooxygenases play an important role in the detoxification of plant toxins and insecticides, leading to insecticides resistance. We investigated the induced effects of xanthotoxin exposure on detoxification enzyme activity and larval tolerance to α-cypermethrin in S. exigua. Our results showed that the lethal concentration (LC 50) of α-cypermethrin for xanthotoxin-exposed larvae was 2.1-fold higher than in the control. Moreover, cytochrome P450 enzyme activity was significantly elevated by upregulation of P450 genes in treated larvae. RT-qPCR results showed that CYP9A10 expression level was significantly increased in all treatments, while maximal expression level was observed in xanthotoxin+α-cypermethrin-fed larvae. RNAi-mediated silencing of CYP9A10 further increased mortality by 18%, 26% and 35% at 48 h and by 27%, 43% and 55% at 72 h when larvae were exposed to diets containing chemicals as compared to the control. The results show that CYP9A10 might play an important role in xanthotoxin and α-cypermethrin detoxification in S. exigua. RNAi-mediated silencing could provide an effective synergistic agent for pest control or insecticide resistance management. Unlabelled Image • Plant secondary metabolites induce insecticide resistance in S. exigua and the activity of insect P450 detoxification enzymes • Xanthotocin induced up-regulation of P450s gene in α-cypermethrin fed Spodoptera exigua larvae • This systematic study enlightening the effect of plant secondary metabolite xanthotoxin on α-cypermethrin sensitivity of S. exigua • Exposure of S. exigua larvae to xanthotocin from host plants may compromise the efficacy of α-cypermethrin insecticides. [ABSTRACT FROM AUTHOR]

Abstract The beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) is a highly polyphagous pest which causes considerable economic losses to cotton and many vegetable crops. Tannins are among the most important secondary metabolites in cotton plants. We show that tannic acid enhances the toxic effect of chlorantraniliprole on S. exigua when presented in combination. Bioassays using third-instar S. exigua larvae on an artificial diet showed that consumption of tannic acid with chlorantraniliprole at the concentration of (2 mg/g and LC 50 0.018 mg/L) had higher toxicity when compared to either chlorantraniliprole or tannic acid alone (LC 50 0.027 mg/L). The diet containing tannic acid with chlorantraniliprole significantly prolonged larval and pupal developmental time and extended mean generation time and total pre-oviposition period compared to either chemical alone. Moreover, fecundity, survival rate, reproductive value, intrinsic rate of increase, finite rate of increase and net reproduction rate declined significantly when exposed to the combined treatment. No difference was observed between tannic acid and the control. Meanwhile, tannic acid with chlorantraniliprole had markedly antifeedant effects; causing significant decline in the relative growth rate (RGR), the relative consumption rate (RCR), the efficiency of conversion of ingested food (ECI), the efficiency of conversion of digested food and an increase in the approximate digestibility (AD) compared to either chemical alone. Tannic acid with chlorantraniliprole also decreased the insect's carbohydrate, lipid and protein contents significantly. The results showed that the interaction between tannic acid and chlorantraniliprole on the growth inhibition of larvae was additive and tannic acid increased the toxicity of chlorantraniliprole to insects. The results of this study provide information useful in integrated pest management programs for S. exigua and show that tannic acid combined with chlorantraniliprole may be a route to reducing the use of synthetic pesticides. Graphical abstract Unlabelled Image Highlights • Tannic acid enhances toxicity of chlorantraniliprole against S. exigua. • Dietary tannic acid & chlorantraniliprole reduces fecundity and fitness of S exigua. • Additive effects decreased the carbohydrate, lipid and protein contents of pest. • Enhancement effect observed in combination tannic acid with insecticide [ABSTRACT FROM AUTHOR]

Beet armyworm Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) is one of the most devastating pests of different key crops. The present study deals with the toxic effect of fenvalerate insecticide on the development, reproduction and the detoxification enzyme's activity of S. exigua feeding on tomato, cabbage, and artificial diet. The developmental period of the second instar to adult emergence was prolonged (16.74 days) reared on tomato followed by cabbage (15.97 days) and artificial diet (15.62 days). The fecundity of S. exigua was lowest on the tomato plant (279 eggs), followed by an artificial diet (347 eggs), while the highest number of eggs was observed on cabbage after the control diet (421eggs). Moreover, the lowest survival rate of the second to the third instar, fourth to the fifth instar, and hatchability were recorded in insects reared on tomato (70.89%) compared to that reared on cabbage (77.08%) and artificial diet (79.66%). S. exigua reared on tomato had the lowest intrinsic rate of increase (r : 0.133) and the highest mean generation time (T: 31.36). Furthermore, detoxifying enzyme activity in S. exigua was much lower on tomato than on cabbage and diet. Moreover, the fenvalerate toxicity was synergized by either piperonyl butoxide (PBO) or S,S,S tributylphosphorotrithioate (DEF) due to the likely participation of monooxygenases or esterase; this suggests a general metabolic resistance. This research provides a solid base for devising an applicable and successful strategy for the controlling the resistance development in beet armyworms. [ABSTRACT FROM AUTHOR]

The beet armyworm, Spodoptera exigua , is a highly polyphagous pest originated from Southeast Asia but has spread globally, attacking economically important crops and fruits. Bistrifluron insecticide is one of the highly active insect growth regulators that has been reported to inhibit development and longevity in other lepidopteran species and could be used in the control of S. exigua. In the present study, the age-stage, two-sex life table technique was applied to assess the sublethal effects of bistrifluron on biological traits and vitellogenin gene (SeVg) expression when 2nd instar larvae fed to sublethal concentrations (LC 10 , LC 20 and LC 40) of bistrifluron. Mean generation time from eggs to adults was longer at LC 40 (37.79 ± 0.81 d) and LC 20 (37.04 ± 0.72) compared to the LC 10 (36.89 ± 0.63 d) and control groups (36.07 ± 0.38 d). Fecundity of female at LC 40 (279.17 ± 42.8 eggs), LC 20 (347 ± 35.4 eggs) and LC 10 (411.58 ± 42.38 eggs) were significantly lower than the control treatment (532.47 ± 7.13). Furthermore, the lower intrinsic rates of increase (LC 40 ; r = 0.1207 ± 0.009, LC 20 ; r = 0.1329 ± 0.009 and LC 10 ; r = 0.14398 ± 0.009 compared to the control r = 0.164 ± 0.0076), was observed along with significantly extended mean generation times (LC 40 ; T = 34.825 ± 0.317 days, LC 20 ; T = 33.27 ± 0.368 days and LC 10 ; T = 31.899 ± 0.398 days compared to the control 30.927 ± 0.255 days). Furthermore, the contents of energy reserve macronutrients (carbohydrate, lipid and protein) significantly reduced in dose and time dependent manner in treated insects as compared to control. Furthermore, the expression level of SeVg mRNA significantly decreased by 43.8% in the female adults when one-day-old second instar larvae were treated with sublethal concentrations of bistrifluron in comparison with the control. Documenting these sublethal effects is a vital, and often overlooked factor, in assessing the overall efficacy of insecticides in the management of pest populations. [Display omitted] • Sublethal effects of bistrifluron insecticide on Spodoptera exigua. • Sublethal concentrations negatively affected key life-history traits of Spodoptera exigua. • The contents of macronutrients (carbohydrate, lipid and protein) significantly reduced in dose and time dependent manner. • Expression level of SeVg gene significantly reduced at sublethal concentrations of bistrifluron. [ABSTRACT FROM AUTHOR]

Plants employ an intricate and dynamic defense system that includes physiological, biochemical, and molecular mechanisms to counteract the effects of herbivorous attacks. In addition to their tolerance to phytotoxins, beet armyworm has quickly developed resistance to deltamethrin; a widely used pyrethroid insecticide in cotton fields. The lethal concentration (LC50) required to kill 50% of the population of deltamethrin to gossypol-fed Spodoptera exigua larvae was 2.34-fold higher than the control group, suggesting a reduced sensitivity as a consequence of the gossypol diet. Piperonyl butoxide (PBO) treatment was found to synergize with deltamethrin in gossypol-fed S. exigua larvae. To counteract these defensive plant secondary metabolites, beet armyworm elevates their production of detoxification enzymes, including cytochrome P450 monooxygenases (P450s). Gossypol-fed beet armyworm larvae showed higher 7-ethoxycoumarin-O-deethylase (ECOD) activities and exhibited enhanced tolerance to deltamethrin after 48 and 72 h when compared to the control. Moreover, gossypol pretreated S. exigua larvae showed faster weight gain than the control group after transferring to a deltamethrin-supplemented diet. Meanwhile, gossypol-induced P450s exhibited high divergence in the expression level of two P450 genes: CYP6AB14 and CYP9A98 in the midgut and fat bodies contributed to beet armyworm tolerance to deltamethrin. Knocking down of CYP6AB14 and CYP9A98, via double-stranded RNAs (dsRNA) in a controlled diet, rendered the larvae more sensitive to the insecticide. These data demonstrate that generalist insects can exploit secondary metabolites from host plants to enhance their defense systems against other toxic chemicals. Impairing this defense pathway by RNA interference (RNAi) holds a potential to eliminate the pest's tolerance to insecticides and, therefore, reduce the required dosages of agrochemicals in pest control. [ABSTRACT FROM AUTHOR]

The beet armyworm, Spodoptera exigua (Hubner), is one of the major crop pests and is a target for current pest control approaches using insecticides. S. exigua melanic mutants (SEM) spontaneously occurred in the S. exigua wild type (SEW) strain and have been maintained under laboratory conditions on an artificial diet. Scanning electron microscopy showed that the inner cuticle of the SEM had a denser and less orderly structure. We investigated the cuticle protein genes using RNA-seq at three different developmental stages of both SEM and SEW. Comparison of cDNA libraries showed that 7257 CPs were significantly up-regulated and 664 genes were significantly downregulated in SEM at the developmental stage of 46-h in the fifth instar. In addition, 460 genes were significantly up-regulated and 439 genes were significantly down-regulated in the SEM at the development stage of 4-h before pupation. Moreover, 162 genes were significantly up-regulated and 293 genes were significantly downregulated in the SEM, just after pupation. Two genes CPR63 and CPR97 were identified from RNA sequences to verify the differentially expressed gene (DEG) results through quantitative real-time PCR (qRT-PCR). The results show that expression of both CPR63 and CPR97 structural cuticular proteins were significantly different between SEM and SEW. This functional analysis may help in understanding the role that these genes play in the cuticle pattern of the SEM. [ABSTRACT FROM AUTHOR]