Reduced neuronal sensitivity and susceptibility of the fall armyworm, Spodoptera frugiperda, to pyrethroids in the absence of known knockdown mutations

https://doi.org/10.1016/j.pestbp.2020.104652Get rights and content

Highlights

  • Insecticide resistance is well documented in Spodoptera frugiperda

  • A neurophysiological assay was developed to bolster molecular genetic data

  • Reduced neural sensitivity corresponded to reduced toxicity to pyrethroids in field populations

  • No known knockdown mutations were identified in field population

  • Management strategies will benefit from combining neurophysiological recordings and molecular genetics

Abstract

Neurophysiological recordings were employed to quantify neuronal sensitivity to neurotoxic insecticides and assessed toxicity across field and laboratory fall armyworm (FAW) populations. Topical toxicity resistance ratios (RR) in field-collected FAW was 767-fold compared to laboratory strains and, importantly, a 1750-fold reduction in potency was observed for λ-cyhalothrin in neurophysiological assays. Field collected FAW were found to have a RR of 12 to chlorpyrifos when compared to the susceptible strain and was 8-fold less sensitive in neurophysiological assays. Surprisingly, there were no point mutations identified in the voltage-gated sodium channel known to cause pyrethroid resistance. For acetylcholinesterase, FAW had more than 80% of their nucleotide sequences consistent with A201 and F290 of the susceptible strains although 60% of the tested population was heterozygous for the G227A mutation. These data indicate that point mutations did not contribute to the high level of pyrethroid resistance and nerve insensitivity in this population of field collected FAW. Additionally, these data suggest the kdr phenotype only explains a portion of the heritable variation in FAW resistance and indicates kdr is not the only predictor of high pyrethroid resistance. Phenotypic assays, such as toxicity bioassays or neurophysiological recordings, using field-collected populations are necessary to reliably predict resistant phenotypes and product failures.

Introduction

The fall armyworm (FAW), Spodoptera frugiperda (Lepidoptera: Noctuiidae), is a polyphagous herbivore that is known to be a major insect pest of multiple economically important row crops, such as corn, cotton, sorghum, and rice (Koffi et al., 2020; Montezano et al., 2018). The ability of FAW to feed on a wide range of host plants, the occurrence of multiple generations in a single growing season, and their ability to migrate make FAW one of the most significant economic pests of the Western Hemisphere. If left uncontrolled, FAW has been documented to cause up to 100% crop yield loss and global economic losses have been estimated to be upwards of $6 billion USD annually (Blanco et al., 2016; C. C. F. A. A. B. International, 2017). In addition to the economic damage, FAW is a serious threat to the food security of millions of people as FAW populations have recently become established across Africa, India, and China (Koffi et al., 2020; Goergen et al., 2016; Sharanabasappa et al., 2018; Wu et al., 2019), which rely heavily on maize and rice as staple food crops. To mitigate these global economic and food security concerns, synthetic insecticides remain a significant component of FAW control programs (Blanco et al., 2016; Brookes and Barfoot, 2016; Gutierrez-Moreno et al., 2019) despite the use of Bacillus thuringiensis technologies. Unfortunately, insecticide use rates have been documented to be extreme as is evidenced by Mexican maize farmers using an estimated 3000 tons of synthetic insecticides per year to control FAW (Blanco et al., 2014) and African countries using copious amounts of synthetic insecticides as an emergency response to slow immigration into new regions of the continent (Fotso Kuate et al., 2019).

As with other insect pests, the evolution of insecticide resistance is likely to be amplified in FAW by the high use rates and limited availability of registered mechanisms of action. Thus, current resistance management practices suggest alternating between five foliar insecticide mechanism of actions based on pre-planting, planting, vegetative, and reproductive stages of the plant as well as incorporating seed treatments and transgenic technologies (I. I. R. A. Committee, 2016). However, despite the implementation of resistance management practices, field-evolved resistance to multiple classes of synthetic insecticides has occurred in many populations across the world (Gutierrez-Moreno et al., 2019), which threatens the efficacy of current FAW control paradigms. Furthermore, although multiple insecticidal classes are available and suggested for use in FAW control programs, pyrethroids and organophosphates remain the most commonly used chemical insecticide classes (B. M. O. Agriculture, 2013).

Pyrethroid resistance in lepidopteran pests is multifactorial and considered to be due to reduced penetration, increased metabolism, and altered target-site sensitivity (Carvalho et al., 2013; Ottea et al., 1995; Nicholson and Miller, 1985; Yu et al., 2003). Furthermore, lambda (λ)-cyhalothrin resistance in FAW was shown to be driven by multiple recessive genes and additional studies have identified three different kdr- and super kdr-type mutations (Carvalho et al., 2013; Rios-Diez and Saldamando-Benjumea, 2011) that are analogous to known house fly gene regions causing insensitivity to pyrethroid insecticides (Miyazaki et al., 1996; Soderlun and Lee, 2001). Although metabolic and non-metabolic mechanisms are known to contribute to reduced pyrethroid susceptibility, the majority of efforts to determine mechanisms of resistance have focused on genetic analyses that identify target-site mutations analogous to kdr mutations established in model arthropod pests. Although this is a general predictor of insecticide sensitivity within that arthropod population, the presence or absence of target-site mutations does not necessarily predict the neuronal sensitivity or resistance ratios (RR) to the insecticide within the population of interest. Therefore, this study aimed to develop an electrophysiological assay to measure the spontaneous activity of the FAW central nervous system and provide a proof-of-concept method for the rapid quantification of reduced potency within a field-collected population of FAW at the level of the nerve.

Section snippets

Compounds and compound synthesis

Permethrin, λ-cyhalothrin, and dichlorvos were all purchased from Sigma-Aldrich Chemical Co. (St. Louis, MO, USA). The organophosphates chlorpyrifos and chlorpyrifos-oxon were purchased through ChemService Inc. (West Chester, PA, USA). All compounds were > 95% purity. Karate Z was generously donated by Dr. Sebe Brown (Assistant Professor, Louisiana State University). The solvents dimethyl sulfoxide (DMSO) and absolute ethanol were purchased from Sigma-Aldrich Chemical Co. A molecular sieve OP

Spontaneous firing rate of thoracic and abdominal ganglia of 3rd-instar FAW

To determine the ideal ganglia to use for determinations of potency for insecticides, we compared the spontaneous discharge frequency of abdominal and thoracic ganglia over a 60-min period. For thoracic ganglia, the mean firing rate was found to be 25 ± 6 Hz at 0–10 min and increased to an average firing rate of 31 ± 5 Hz, 31 ± 4 Hz, 29 ± 3 Hz for 10–20 min, 20–30 min, and 30–40 min, respectively, which were not significantly different from each other (Fig. 1C). A significant (p < .05)

Discussion

Previous studies have investigated the biochemical, molecular, and genomic characteristics of pyrethroid and organophosphate resistance in FAW with data indicating multiple mechanisms for insecticide resistance (Carvalho et al., 2013; Yu et al., 2003). Multiple mechanisms of pyrethroid resistance of other lepidopteran pests, such as H. virescens, has also been documented and it was suggested that expression of enhanced metabolism in the absence of reduced target-site sensitivity is inadequate

Declaration of Competing Interest

The authors declare no conflicts of interest.

Acknowledgements

We thank Dr. Sebe Brown (LSU, Entomology) from Macon Ridge Research Station in Winnsboro, Louisiana for providing farm plots of late corn to collect S. frugiperda and for providing Karate Z. We also thank Dr. Mike Stout (LSU, Entomology) for assistance with rearing S. frugiperda. Funding provided by USDA Hatch grant number CT-0273 (project # 94313), Louisiana Board of Regents (LEQSF(2016–2019)-RD-A-26; PI Swale).

References (46)

  • J.R. Bloomquist et al.

    Reduced neuronal sensitivity to dieldrin and picrotoxinin in a cyclodiene-resistant strain of Drosophila melanogaster (Meigen)

    Arch. Insect Biochem. Physiol.

    (1992)
  • L.P. Brito et al.

    Levels of resistance to Pyrethroid among distinct kdr alleles in Aedes aegypti laboratory lines and frequency of kdr alleles in 27 natural populations from Rio de Janeiro, Brazil

    Biomed. Res. Int.

    (2018)
  • G. Brookes et al.

    Environmental impacts of genetically modified (GM) crop use 1996-2014: impacts on pesticide use and carbon emissions

    GM Crops Food

    (2016)
  • C. C. F. A. A. B. International

    New Report Reveals Cost of Fall Armyworm to Farmers in Africa, Provides Recommendations for Control

    (2017)
  • R.A. Carvalho et al.

    Investigating the molecular mechanisms of organophosphate and pyrethroid resistance in the fall armyworm Spodoptera frugiperda

    PLoS One

    (2013)
  • R. Chen et al.

    Inwardly rectifying potassium (Kir) channels represent a critical ion conductance pathway in the nervous systems of insects

    Sci. Rep.

    (2018)
  • G.I. Diez-Rodriguez et al.

    Heranc ̧a da re- sisteˆncia de Spodoptera frugiperda (J.E. Smith) (Lepi- doptera: Noctuidae) a lambda-cialotrina

    Neotrop. Entomol.

    (2001)
  • K. Dong

    Insect sodium channels and insecticide resistance

    Invertebr. Neurosci.: IN

    (2007)
  • R.H. ffrench-Constant et al.

    Why are there so few resistance-associated mutations in insecticide target genes?

    Philos. Trans. R. Soc. Lond. Ser. B Biol. Sci.

    (1998)
  • S.P. Foster

    A mutation (L1014F) in the voltage-gated sodium channel of the grain aphid, Sitobion avenae, is associated with resistance to pyrethroid insecticides

    Pest Manag. Sci.

    (2014)
  • A. Fotso Kuate

    Spodoptera frugiperda smith (Lepidoptera: Noctuidae) in Cameroon: case study on its distribution, damage, pesticide use, genetic differentiation and host plants

    PLoS One

    (2019)
  • G. Goergen et al.

    First report of outbreaks of the fall armyworm Spodoptera frugiperda (J E smith) (Lepidoptera, Noctuidae), a new alien invasive Pest in west and Central Africa

    PLoS One

    (2016)
  • J.W. Gordy et al.

    Comparative effectiveness of potential elicitors of plant resistance against Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) in four crop plants

    PLoS One

    (2015)
  • Cited by (9)

    • Toxicological analysis of stilbenes against the fall armyworm, Spodoptera frugiperda

      2021, Pesticide Biochemistry and Physiology
      Citation Excerpt :

      The laboratory colony of FAW used in this study, referred to as LSU-Lab-1 (McComic et al., 2020), was initially established in 2005 from cotton fields at the Macon Ridge Research Station in Winnsboro, Louisiana. LSU-Lab-1 was genetically confirmed as being the corn-strain (McComic et al., 2020) and was maintained as previously described (McComic et al., 2020; Gordy et al., 2015). Caterpillars were reared on artificial diet (Stonefly Heliothis Diet, Ward's Natural Science, Rochester, NY, USA) in 30-mL plastic cups.

    • Identification of yellow gene family and functional analysis of Spodoptera frugiperda yellow-y by CRISPR/Cas9

      2021, Pesticide Biochemistry and Physiology
      Citation Excerpt :

      The results showed that CRISPR/Cas9 system was efficient availability for this species. This also could be helpful for studying functional roles of detoxification genes or modes of action of insecticides in this insect pest, such as pyrethroids resistance mechanism in the absence of known knockdown mutations (McComic et al., 2020), ABC genes which related to Bt toxins resistance (Boaventura et al., 2020b), the relationship between AChE point mutation and organophosphates resistance (Zhao et al., 2020). Besides, the further results showed that yellow-y gene played important roles not only in cuticle pigmentation at both larval and adult stages, and also in the normal development and reproduction respectively for larvae and adults.

    View all citing articles on Scopus
    View full text