RNAi-mediated knockdown of papilin gene affects the egg hatching in Nilaparvata lugens.

BACKGROUND: The brown planthopper (BPH), Nilaparvata lugens, is one of the most destructive pests of rice. Owing to the rapid adaptation of BPH to many pesticides and resistant varieties, identifying putative gene targets for developing RNA interference (RNAi)-based pest management strategies has received much attention for this pest. The glucoprotein papilin is the most abundant component in the basement membranes of many organisms, and its function is closely linked to development. RESULTS: In this study, we identified a papilin homologous gene in BPH (NlPpn). Quantitative Real-time PCR analysis showed that the transcript of NlPpn was highly accumulated in the egg stage. RNAi of NlPpn in newly emerged BPH females caused nonhatching phenotypes of their eggs, which may be a consequence of the maldevelopment of their embryos. Moreover, the transcriptomic analysis identified 583 differentially expressed genes between eggs from the dsGFP- and dsNlPpn-treated insects. Among them, the 'structural constituent of cuticle' cluster ranked first among the top 15 enriched GO terms. Consistently, ultrastructural analysis unveiled that dsNlPpn-treated eggs displayed a discrete and distorted serosal endocuticle lamellar structure. Furthermore, the hatchability of BPH eggs was also successfully reduced by the topical application of NlPpn-dsRNA-layered double hydroxide nanosheets onto the adults. CONCLUSION: Our findings demonstrate that NlPpn is essential to maintaining the regular structure of the serosal cuticle and the embryonic development in BPH, indicating NlPpn could be a potential target for pest control during the egg stage. © 2024 Society of Chemical Industry.

Tissue-specific regulation of volatile emissions moves predators from flowers to attacked leaves.

Plant-predator mutualisms have been widely described in nature.1,2 How plants fine-tune their mutualistic interactions with the predators they recruit remains poorly understood. In the wild potato (Solanum kurtzianum), predatory mites, Neoseiulus californicus, are recruited to flowers of undamaged plants but rapidly move downward when the herbivorous mites, Tetranychus urticae, damage leaves. This "up-down" movement within the plant corresponds to the shift of N. californicus from palynivory to carnivory, as they change from feeding on pollen to herbivores when moving between different plant organs. This up-down movement of N. californicus is mediated by the organ-specific emissions of volatile organic compounds (VOCs) in flowers and herbivory-elicited leaves. Experiments with exogenous applications, biosynthetic inhibitors, and transient RNAi revealed that salicylic acid and jasmonic acid signaling in flowers and leaves mediates both the changes in VOC emissions and the up-down movement of N. californicus. This alternating communication between flowers and leaves mediated by organ-specific VOC emissions was also found in a cultivated variety of potato, suggesting the agronomic potential of using flowers as reservoirs of natural enemies in the control of potato pests.

Silver and copper-oxide nanoparticles prepared with GA3 induced defense in rice plants and caused mortalities to the brown planthopper, Nilaparvata lugens (Stål).

BACKGROUND: Nanoparticles have been employed as nanopesticides for pest control in agriculture. However, the harmful effects of their chemical synthesis on human and environmental health have resulted in increased use of green synthetic approaches, including the use of plant extracts. The brown planthopper, Nilaparvata lugens (Stål) (BPH), is a severe pest of rice plants (Oryza sativa L.), especially in Asia. It is usually controlled chemically but has developed resistance against many insecticides. RESULTS: In this study, we synthesized metallic silver (Ag-NPs) and copper-oxide (CuO-NPs) nanoparticles using the exogenous phytohormone, gibberellic acid (GA3), as a reducing agent. We then sprayed them separately on rice plants and BPH together and evaluated their effects on the plants and insects. SEM and TEM images showed that the synthesis was successful, indicated by the sizes (25-60 nm), uniform shape and spherical and cubical structures of Ag-NPs, as well as by the rugby sheet-like of CuO-NPs with lateral sizes of 150-340 nm and thickness of 30-70 nm. Independent applications of the nanoparticles and GA3 on rice plants induced different volatile profiles, of which the highest number emitted was under Ag-NPs, including the highest emission of linalool. Transcriptome analysis showed that Ag-NPs-treated rice plants showed different transcriptome profiles compared to the control, 24 h after treatment, including the upregulation of the linalool synthase gene, genes of plants transcription factors such as WRKY, bHLH and NAC and other genes involved in plant defense responses. In all treatments, the mortality rate of BPH increased with an increase in NPs concentrations over time but was prominent under Ag-NPs treatment. The LC50 values for Ag-NPs and CuO-NPs decreased with an increase in time. Also, the nanoparticles increased the activities of protective enzymes (POD, SOD and CAT), inhibited that of detoxification enzymes (A-CHE, ACP and AKP), and reduced total protein concentrations in the BPH. CONCLUSIONS: These results show that synthesizing nanoparticles using phytohormones may be a safer and environmentally friendly option, which also holds promise for controlling the BPH in rice production.

Heat stress affects potato's volatile emissions that mediate agronomically important trophic interactions.

Potato, a cool-weather crop, emits volatile organic compounds (VOCs) which attract the specialist herbivore, Phthorimaea operculella, but also this herbivore's parasitic wasp, Trichogramma chilonis, an important biocontrol agent. What happens to this trophic system when heat stress challenges this agro-ecosystem? We studied how high temperature (HT) pre-treatments influence potato's VOC emissions and their subsequent effects on the preferences of insects, as evaluated in oviposition assays and Y-tube olfactometers. HT pre-stressed plants were less attractive to P. operculella adult moths, which were repelled by HT VOCs, but increased the recruitment of the parasitoid, T. chilonis, which were attracted. VOC emissions, including the most abundant constituent, ß-caryophyllene, were enhanced by HT treatments; some constituents elicited stronger behavioural responses than others. Transcripts of many genes in the biosynthetic pathways of these VOCs were significantly enhanced by HT treatment, suggesting increases in de novo biosynthesis. HT increased the plant's stomatal apertures, and exogenous applications of the hormone, ABA, known to suppress stomatal apertures, reduced leaf volatile emissions and affected the HT-altered plant attractions to both insects. From these results, we infer that HT stress affects this plant-insect interaction through its influence on VOC emissions, potentially decreasing herbivore ovipositions while increasing ovipositions of the parasitoid.

Plasticity in life features, parasitism and super-parasitism behavior of Bracon hebetor, an important natural enemy of Galleria mellonella and other lepidopteran host species.

The wasp, Bracon hebetor Say, is an important potential biocontrol agent of a wide range of lepidopteran insect species. The current study was subjected to compare these ectoparasitoid fitness traits on different host species belonging to the order Lepidoptera. Moreover, we determine the population dynamic with different host densities, sex ratio patterns, super-parasitism, longevity, paralysis success, and reproductive potential under laboratory conditions. Our results revealed that oviposition increased with an increase in host density, while the adult emergence and egg hatching were decreased due to the super-parasitism on host larvae. A higher male and female-biased population were observed when virgin and mated females offered fresh hosts. Adults' longevity was recorded more in females than males when kept only with bee honey + royal jelly + host larvae. The mean duration of egg-adult development was recorded higher on Galleria mellonella and lowest on Busseola fusca. The parasitization rate, super-parasitism, and cumulative fecundity of mated and virgin female wasps with different host species were observed higher on specific host Galleria mellonella while it was lower on Phthorimaea operculella. Furthermore, the parasitoids having mating experience preferred fresh, while the parasitoids' lack of mating experiences preferred paralyzed host under olfactometer test. Besides, this research has produced novel facts on the biology of parasitic wasp, B. hebetor that may guide the advancement of sustainable biological control programs to control lepidopteran pests.