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Background: Molecular genetic approaches have become vital to understanding the evolutionary processes that act on insect pest populations. From mapping the development of resistance to monitoring and predicting pest movement, genomic tools can inform and enhance pest management programs. Here, we used whole genome sequencing population genomics to unravel novel patterns of population structure, linkage, and selection across the genome of a notorious agricultural pest, the fall armyworm. Results: Our data strongly support the existence of two genetically distinct strains of fall armyworm in North America, which have previously been referred to as the C-strain and the R-strain. Although these strains have diverged genetically, we find that differentiation is not uniform across the genome. The Z-chromosome appears to drive divergence between strains with high levels of linkage observed across this chromosome. We also show that a region of the Z-chromosome containing a circadian clock gene implicated in allochronic reproductive isolation is under strain-specific selection. Our data indicates that strains differ in their geographic distributions and exhibit distinct patterns of geographic sub-structuring indicative of unique dispersal patterns. We provide the first evidence for nuclear genomic differentiation between the two major overwintering populations of fall armyworm in the US. Finally, our data reveal population-specific patterns of selection on genomic regions containing putative insecticide resistance alleles, which could relate to their biogeography. Conclusions: Our results support the existence of the fall armyworm as a pest dyad in the US, with genetically-distinct strains differing in their population structure, dispersal patterns, and genomic signatures of selection on regions likely involved reproductive isolation and insecticide resistance. These differences should be considered when devising and implementing management strategies. [ABSTRACT FROM AUTHOR]

We investigated select transgenic lines of Gossypium hirsutum that over-express AtRAV1 or AtABI5 transcription factors. The hypothesis is that these lines have enhanced responses to abscisic acid (ABA) resulting in greater water use efficiencies (WUE). We measured leaf surface temperatures (LST), stomatal density, absolute and relative sizes of guard cell apertures, and ABA concentrations in cotyledons. We characterized transgene protein expression and activities in transient assays in Nicotiana benthamiana, in transgenic cotton seeds by immunoblot and by endogenous expression in leaves of an effector of ABA responses (GhDREB). AtRAV11-1-5 and AtABI51-1-1 over-expression lines had trends of lower levels of ABA in well-watered and drought-stressed cotyledons, and all events tested had higher leaf stomatal conductance and photosynthesis rates under drought in greenhouse, and lower LSTs than control Coker 312 under drought stress conditions. Notably, AtRAV11-1-5 cotyledons had significantly higher stomatal densities and 26% smaller guard cell apertures than Coker 312 under drought stress, providing a plausible explanation why LSTs across lines were lower concordant with smaller stomatal apertures. These traits may contribute to intrinsic WUE and assimilate traits of larger leaf areas and longer boll fibers previously shown in these and several independent AtRAV1 and AtABI5 events in the greenhouse and field. These results are consistent with the hypothesis that over-expression of AtRAV1 results in an ABA-hypersensitive phenotype manifest as reduced expression of endogenous GhDREB effector, and lower levels of endogenous ABA in cotyledons associated with greater reductions in pore apertures during stress and increased stomatal density.

The fall armyworm, Spodoptera frugiperda (J.E. Smith), is comprised of two genetically distinct strains that are morphologically identical yet exhibit differences in their behavior and physiology (C-strain and R-strain). Evidence of ongoing genetic differentiation between strains highlights the importance of considering strain identity in research and management of fall armyworm populations, but the logistical and technical burden of genotyping limits strain-specific applications. Controlled experiments with laboratory colonies have shown that the strains engage in allochronic ("allo" – different, "chronic" – time) mating behavior, with C-strain mating early in the evening (0–5 hours after sunset) and R-strain mating late in the evening (5–10 hours after sunset). Using temporal field collections and genotype data, we show that strain-specific variation in allochronic male mating behavior occurs across Texas and Florida fall armyworm populations, both of which act as primary source populations for annual migrations of this pest into the continental United States. Time of capture in pheromone traps was significantly different between strains in both Texas and Florida, with the R-strain males consistently being collected in the traps late in the night. The C-strain males were generally captured earlier in the night than their R-strain counterparts, though there was notable variation in the timing between nights and across locations. Allochronic behavior in field populations is consistent with previous laboratory studies reporting differences in the timing of mating between the strains, however increased variability in behavior within and across native populations was observed. Although allochronic behavior in local populations may partially contribute to reproductive isolation between the strains, the behavior is not consistent enough to serve as a complete reproductive barrier. Furthermore, the observed variability in behavior both within and between independent sampling events, especially in the C-strain, poses a challenge to the development of models that utilize time of capture as a predictive phenotype for monitoring strain identity in local populations. [ABSTRACT FROM AUTHOR]

Insect crop pests threaten global food security. This threat is amplified through the spread of nonnative species and through adaptation of native pests to control measures. Adaptations such as pesticide resistance can result from selection on variation within a population, or through gene flow from another population. We investigate these processes in an economically important noctuid crop pest, Helicoverpa zea , which has evolved resistance to a wide range of pesticides. Its sister species Helicoverpa armigera , first detected as an invasive species in Brazil in 2013, introduced the pyrethroid-resistance gene CYP337B3 to South American H. zea via adaptive introgression. To understand whether this could contribute to pesticide resistance in North America, we sequenced 237 H. zea genomes across 10 sample sites. We report H. armigera introgression into the North American H. zea population. Two individuals sampled in Texas in 2019 carry H. armigera haplotypes in a 4 Mbp region containing CYP337B3. Next, we identify signatures of selection in the panmictic population of nonadmixed H. zea , identifying a selective sweep at a second cytochrome P450 gene: CYP333B3. We estimate that its derived allele conferred a ∼5% fitness advantage and show that this estimate explains independently observed rare nonsynonymous CYP333B3 mutations approaching fixation over a ∼20-year period. We also detect putative signatures of selection at a kinesin gene associated with Bt resistance. Overall, we document two mechanisms of rapid adaptation: the introduction of fitness-enhancing alleles through interspecific introgression, and selection on intraspecific variation. [ABSTRACT FROM AUTHOR]

Nearly all herbivorous arthropods make foraging-decisions on individual leaves, yet systematic investigations of the adaptive significance and ecological factors structuring these decisions are rare with most attention given to chewing herbivores. This study investigated why an intracellular feeding herbivore, Western flower thrips (WFT) Frankliniella occidentalis Pergande, generally avoids feeding on the adaxial leaf surface of cotton cotyledons. WFT showed a significant aversion to adaxial-feeding even when excised-cotyledons were turned up-side (abaxial-side 'up'), suggesting that negative-phototaxis was not a primary cause of thrips foraging patterns. No-choice bioassays in which individual WFT females were confined to either the abaxial or adaxial leaf surface showed that 35% fewer offspring were produced when only adaxial feeding was allowed, which coincided with 32% less plant feeding on that surface. To test the hypothesis that leaf biomechanical properties inhibited thrips feeding on the adaxial surface, we used a penetrometer to measure two variables related to the 'toughness' of each leaf surface. Neither variable negatively co-varied with feeding. Thus, while avoiding the upper leaf surface was an adaptive foraging strategy, the proximate cause remains to be elucidated, but is likely due, in part, to certain leaf properties that inhibit feeding.

BACKGROUND: Nonpathogenic fungi associated with plants can enhance plant defenses against stress factors, including herbivory. This study assessed whether cotton plants grown from seeds treated with different fungi affected boll weevil, Anthonomus grandis grandis Boheman, development and reproduction along with plant tolerance. We used whole plants grown from seeds treated with different fungi (Chaetomium globosum TAMU520 and TAMU559, Phialemonium inflatum TAMU490, and Beauveria bassiana) versus non‐treated controls to test insect growth, reproduction, and plant tolerance assays in a greenhouse. RESULTS: Regarding boll weevil reproduction, fewer larvae hatched and fewer adults emerged from fungal‐treated plants. In addition, the developmental time from oviposition to adult emergence was delayed in the plants treated with all fungi. For plant tolerance, B. bassiana‐treated plants attacked by boll weevils shed fewer squares than nonfungal‐treated plants. CONCLUSION: Fungal treatments can affect boll weevil performance and reproduction on cotton plants, with potentially negative effects on population growth. Collectively, these results support the potential for cottonseed treatments with fungi as a novel tool for boll weevil management in the field. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]