Parasitoids of herbivores exploit inducible plant volatiles to find plants with potential hosts from a distance, whereas at close range they typically use host-derived cues to pinpoint and identify suitable hosts. Here, we show, however, that the egg parasitoid Trichogramma japonicum assesses host egg quality far more efficiently by remotely using oviposition-induced plant volatiles (OIPVs). In olfactometer assays, female T. japonicum wasps showed a strong preference for the odor of rice plants carrying 2-day-old eggs of the rice leaf folder Cnaphalocrocis medinalis over the odor of plants with younger or older eggs, a preference that correlated with higher parasitism rates. In accordance with the preference-performance hypothesis, the offspring of T. japonicum showed superior performance in 2-day-old eggs, including shorter development times and higher eclosion rates. Volatile analysis revealed significantly increased emission of D-limonene and α-pinene from plants with 2-day-old eggs, and we found that synthetic versions of these two monoterpenes were highly attractive to the wasp. Knockout rice plants deficient in D-limonene and α-pinene synthesis lost their appeal to the wasps, but attraction could be restored by dispensing synthetic versions of the attractants alongside the knockouts. These findings reveal a novel and highly efficient host-assessment strategy in egg parasitoids, whereby plant-provided cues inform the wasps about host quality from afar. This discovery is illustrative of the clever strategies that have evolved out of plant-insect interactions and offers fresh ideas to optimally exploit plant traits for biocontrol approaches against C. medinalis, a major rice pest.

Athelia rolfsii is a devastating soilborne pathogen that causes stem rot of peanut and severely restricts peanut production. The new generation of succinate dehydrogenase inhibitor (SDHI) fungicide benzovindiflupyr has been registered in the United States and Brazil for managing multiple plant diseases. However, it is not registered in China to control peanut stem rot. In this study, 246 isolates from major peanut production areas in Shandong, Henan, and Hebei Provinces of China were used to determine the baseline sensitivity of A. rolfsii to benzovindiflupyr. The frequency of EC₅₀ values of benzovindiflupyr was unimodally distributed with an average EC₅₀ of 0.12 ± 0.05 mg/liter and a range of 0.01 to 0.57 mg/liter. Benzovindiflupyr can also strongly inhibit the germination of sclerotia, with an average EC₅₀ of 2.38 ± 1.04 mg/liter (n = 23). In addition, benzovindiflupyr exhibited great in vivo efficacy against A. rolfsii; the protective or curative efficacy (89.87%, 20.39%) of benzovindiflupyr at a concentration of 50 mg/liter was equivalent to that of the control fungicide thifluzamide at 100 mg/liter (86.39%, 16.21%). At the same concentration (e.g., 100 mg/liter), the protective efficacy (93.99%) of benzovindiflupyr was more than twice as high as the curative efficacy (45.07%). A positive correlation existed between benzovindiflupyr and isopyrazam or mefentrifluconazole, which possibly resulted from similar chemical structures or damage to the cell membrane. Our findings provide valuable information for the application of benzovindiflupyr, and the established baseline sensitivity could facilitate the monitoring and assessment of benzovindiflupyr resistance risk.

Reference genes are important for the accuracy of gene expression profiles using reverse-transcription quantitative PCR (RT-qPCR). However, there are no available reference genes reported for Sclerotium rolfsii; it actually has a pretty diverse and wide host range. In this study, seven candidate reference genes (UBC, β-TUB, 28S, 18S, PGK, EF1α and GAPDH) were validated for their expression stability in S. rolfsii under conditions of different developmental stages, populations, fungicide treatments, photoperiods and pHs. Four algorithm programs (geNorm, Normfinder, Bestkeeper and ΔCt) were used to evaluate the gene expression stability, and RefFinder was used to integrate the ranking results of four programs. Two reference genes were recommended by RefFinder for RT-qPCR normalization in S. rolfsii. The suitable reference genes were GAPDH and UBC across developmental stages, PGK and UBC across populations, GAPDH and PGK across fungicide treatments, EF1α and PGK across photoperiods, β-TUB and EF1α across pHs and PGK and GAPDH across all samples. Four target genes (atrB, PacC, WC1 and CAT) were selected for the validation of the suitability of selected reference genes. However, using one or two reference genes in combination to normalize the expression of target genes showed no significant difference in S. rolfsii. In short, this study provided reliable reference genes for studying the expression and function of genes in S. rolfsii.

The homeotic gene Antennapedia (Antp) has been identified as playing a pivotal role in the morphogenesis of the thorax and wings across various insect species. Leveraging insights from previous studies, the functional characterization of Antp in S. frugiperda was undertaken using RT-qPCR and the CRISPR/Cas9 genome-editing system. Phylogenetic analyses indicate that Antp shares a high degree of sequence homology among Lepidoptera species. The expression profile of SfAntp was detected by RT-qPCR. The results showed that SfAntp was expressed in the whole growth cycle of S. frugiperda, the expression level was the highest in the egg stage, and the expression level was higher from 12 h to 48 h. Tissue-specific expression profiling demonstrated that SfAntp was most abundantly expressed in the thoracic segments and legs. To functionally disrupt SfAntp, two sgRNA sites were designed at the first exon of SfAntp and the gene was knocked out by CRISPR/Cas9 via microinjection. The results showed that the deletion of SfAntp produced a mutant phenotype of thoracic fusion, thoracic leg defect, leg-like protrusions between the head and thoracic segments and pupation deformity. In addition, deletion of SfAntp resulted in high embryo mortality. Through DNA sequencing, it was found that the target site of the SfAntp mutant had different degrees of frameshift mutations, indicating that the mutant phenotype was indeed caused by the knockout of SfAntp.

The family Elateridae, known as click beetles, is a mega-diverse lineage of Coleoptera. Wireworms are the larval stage of click beetles, which are generalist herbivores and which are recognized as economically important pests of crops. To more effectively control and monitor wireworms, it is crucial to understand the genetics, taxonomy and phylogenetics of Elateridae. Here, we sequenced and characterized three complete mitochondrial genomes (mitogenomes) from the subfamily Elaterinae using a next-generation sequencing approach. In addition, we provided the annotated mitogenomes of the newly sequenced species, namely Parasilesis musculus (Candèze, 1873), Melanotus cribricollis Candèze, 1860 and Glyphonyx sp., and compared their arrangement with other closely related species. The secondary structures of tRNA genes and rRNA genes were predicted. Combined with the published mitogenomes of elaterid species, we reconstructed the phylogenetic framework for Elateridae under maximum likelihood and Bayesian inference methods using nucleotide and amino acid sequence datasets separately. The results from the Bayesian analysis based on the nucleotide dataset PCGRNA including all 37 mitochondrial genes were congruent with previous studies. Within the monophyletic Elateridae, two main clades were recovered. The first clade included Elaterinae and Melanotus. The second clade consisted of the remaining subfamilies. Physodactylinae and Cardiophorinae formed a sister group. Agrypninae was monophyletic. A subclade comprised Negastriinae and Dendrometrinae.