Root-Associated Entomopathogenic Fungi Modulate Their Host Plant’s Photosystem II Photochemistry and Response to Herbivorous Insects

The escalating food demand and loss to herbivores has led to increasing interest in using resistance-inducing microbes for pest control. Here, we evaluated whether root-inoculation with fungi that are otherwise known as entomopathogens improves tomato (Solanum lycopersicum) leaflets’ reaction to herbivory by Spodoptera exigua (beet armyworm) larvae using chlorophyll fluorescence imaging. Plants were inoculated with Metarhizium brunneum or Beauveria bassiana, and photosystem II reactions were evaluated before and after larval feeding. Before herbivory, the fraction of absorbed light energy used for photochemistry (ΦPSII) was lower in M. brunneum-inoculated than in control plants, but not in B. bassiana-inoculated plants. After herbivory, however, ΦPSII increased in the fungal-inoculated plants compared with that before herbivory, similar to the reaction of control plants. At the same time, the fraction of energy dissipated as heat (ΦNPQ) decreased in the inoculated plants, resulting in an increased fraction of nonregulated energy loss (ΦNO) in M. brunneum. This indicates an increased singlet oxygen (1O2) formation not detected in B. bassiana-inoculated plants, showing that the two entomopathogenic fungi differentially modulate the leaflets’ response to herbivory. Overall, our results show that M. brunneum inoculation had a negative effect on the photosynthetic efficiency before herbivory, while B. bassiana inoculation had no significant effect. However, S. exigua leaf biting activated the same compensatory PSII response mechanism in tomato plants of both fungal-inoculated treatments as in control plants.

Diversity of Insect Pests and Ecofriendly Fauna Inhabiting Chickpea (Cicer arietinum L.) Agro-Ecosystem in Bundelkhand Region of Uttar Pradesh

An experiment was conducted at Agricultural Research Farm of Brahmanand Post Graduate College, Rath, Hamirpur (U.P.) during 2016-17 and 2019-20 cropping season. In the Bundelkhand agro climatic region seventeen species of insect belonging to seven orders and twelve families were recorded from chickpea agro ecosystem. Among which six species from Lepidoptera, four species from hymenoptera, two species from coleoptera and odonata and one species from hemiptera, isoptera, and dyctyoptera were identified. On the basis of economic importance nine species were insect pests, five species were predators, two species were insect parasitoids and one species was insect pollinator. Among the nine species of insect pests, chickpea pod borer, Helicoverpa armigera Hub. and gram cut worm, Agrotis ipsilon (Huf.) occurred regularly and chickpea pod borer was designated as a major pest while, gram cut worm infested with very low population density and considered as minor insect pest of chickpea. The five species of insect pest occurred occasionally i.e. armyworm, Mythmina separate (walker), tobacco caterpillar, Spodoptera litura (Fab), cow pea aphid, Aphis craccivora (Koch), termite, Odentotermes obesus (Rambur) and black flea beetle, Altica Species (unidentified species) were designated as minor pest of chickpea. While, two species namely, Bihar hairy caterpillar, Spilarctia obliqua (Walker) and beet armyworm, Spodoptera oxiqua (Hub) occurred intermittently in sporadic manner and designated as stray pest of chickpea. The eight species of insect’s ecofriendly fauna inhabiting chickpea agro ecosystem were observed, among which five species of predators, two species of parasitoids and one species of pollinators foraged on chickpea crop occasionally in very low population density. The maximum number of ecofriendly fauna was of the order hymenoptera, two species of parasitoids, one species of predators and pollinator i.e. Trichogrammatid wasp, Trichogramma chilonis (Ishii), ichneumonid wasp, Campoletis chloridae (Uchida), common yellow wasp, Vespa oreintalis (L.) and small honeybee, Apis floraea followed by odonata i.e. dragonfly, Croccothemis servielia (Drury) and damsel fly, Agriocnemis pygmiea (Rambur), coleoptera, rove beetle, Alleochara billienata and dyctyoptera, praying mantis, Mantis religiosa (L.).

Signatures of plant defense response specificity mediated by herbivore-associated molecular patterns in legumes

Chewing herbivores activate plant defense responses through a combination of mechanical wounding and elicitation by herbivore associated molecular patterns (HAMPs). HAMPs are wound response amplifiers; however, specific defense outputs may also exist that strictly require HAMP-mediated defense signaling. To investigate HAMP-mediated signaling and defense responses, we characterized cowpea transcriptome changes following elicitation by inceptin, a peptide HAMP common in Lepidoptera larvae oral secretions. Following inceptin treatment, we observed large-scale reprogramming of the transcriptome consistent with 3 different response categories: 1) amplification of mechanical wound responses, 2) temporal extension through accelerated or prolonged responses, and 3) examples of inceptin-specific elicitation and suppression. At both early and late timepoints, namely 1 and 6 hours, large sets of transcripts specifically accumulated following inceptin elicitation but not wounding alone. Further inceptin-regulated transcripts were classified as reversing changes induced by wounding alone. Within key signaling and defense related gene families, inceptin-elicited responses commonly targeted select subsets of wound-induced transcripts. Transcripts displaying the largest inceptin-elicited fold-changes included terpene synthases (TPS) and peroxidases (POX) that correspond with induced volatile production and increased peroxidase activity in cowpea. Characterization of inceptin-elicited cowpea defenses via heterologous expression in Nicotiana benthamiana demonstrated that specific cowpea TPS and POX were able to confer terpene emission and the reduced growth of beet armyworm (Spodoptera exigua) herbivores, respectively. Collectively, our present findings in cowpea support a model where HAMP-elicitation both amplifies concurrent wound responses and specifically contributes to the activation of selective outputs associated with direct and indirect anti-herbivore defenses.

Genome and transcriptome analysis of the beet armyworm Spodoptera exigua reveals targets for pest control

The genus Spodoptera (Lepidoptera: Noctuidae) includes some of the most infamous insect pests of cultivated plants including Spodoptera frugiperda, Spodoptera litura and Spodoptera exigua. To effectively develop targeted pest control strategies for diverse Spodoptera species, genomic resources are highly desired. To this aim, we provide the genome assembly and developmental transcriptome comprising all major life stages of S. exigua, the beet armyworm. Spodoptera exigua is a polyphagous herbivore that can feed on > 130 host plants, including several economically important crops. The 419 Mb beet armyworm genome was sequenced from a female S. exigua pupa. Using a hybrid genome sequencing approach (Nanopore long read data and Illumina short read), a high-quality genome assembly was achieved (N50=1.1 Mb). An official gene set (OGS, 18,477 transcripts) was generated by automatic annotation and by using transcriptomic RNA-seq data sets of 18 S. exigua samples as supporting evidence. In-depth analyses of developmental stage-specific expression combined with gene tree analyses of identified homologous genes across Lepidoptera genomes revealed four potential genes of interest (three of them Spodoptera-specific) upregulated during 1st and 3rd instar larval stages for targeted pest-outbreak management. The beet armyworm genome sequence and developmental transcriptome covering all major developmental stages provide critical insights into the biology of this devastating polyphagous insect pest species worldwide. In addition, comparative genomic analyses across Lepidoptera significantly advance our knowledge to further control other invasive Spodoptera species and reveals potential lineage-specific target genes for pest control strategies.

Genome mapping coupled with CRISPR gene editing reveals a P450 gene confers avermectin resistance in the beet armyworm

The evo of insecticide resistance represents a global constraint to agricultural production. Because of the extreme genetic diversity found in insects and the large numbers of genes involved in insecticide detoxification, better tools are needed to quickly identify and validate the involvement of putative resistance genes for improved monitoring, management, and countering of field-evolved insecticide resistance. The avermectins, emamectin benzoate (EB) and abamectin are relatively new pesticides with reduced environmental risk that target a wide number of insect pests, including the beet armyworm, Spodoptera exigua, an important global pest of many crops. Unfortunately, field resistance to avermectins recently evolved in the beet armyworm, threatening the sustainable use of this class of insecticides. Here, we report a high-quality chromosome-level assembly of the beet armyworm genome and use bulked segregant analysis (BSA) to identify the locus of avermectin resistance, which mapped on 15–16 Mbp of chromosome 17. Knockout of the CYP9A186 gene that maps within this region by CRISPR/Cas9 gene editing fully restored EB susceptibility, implicating this gene in avermectin resistance. Heterologous expression and in vitro functional assays further confirm that a natural substitution (F116V) found in the substrate recognition site 1 (SRS1) of the CYP9A186 protein results in enhanced metabolism of EB and abamectin. Hence, the combined approach of coupling gene editing with BSA allows for the rapid identification of metabolic resistance genes responsible for insecticide resistance, which is critical for effective monitoring and adaptive management of insecticide resistance.