Induction of defense in cereals by 4-fluorophenoxyacetic acid suppresses insect pest populations and increases crop yields in the field.

Synthetic chemical elicitors, so called plant strengtheners, can protect plants from pests and pathogens. Most plant strengtheners act by modifying defense signaling pathways, and little is known about other mechanisms by which they may increase plant resistance. Moreover, whether plant strengtheners that enhance insect resistance actually enhance crop yields is often unclear. Here, we uncover how a mechanism by which 4-fluorophenoxyacetic acid (4-FPA) protects cereals from piercing-sucking insects and thereby increases rice yield in the field. Four-FPA does not stimulate hormonal signaling, but modulates the production of peroxidases, H2O2, and flavonoids and directly triggers the formation of flavonoid polymers. The increased deposition of phenolic polymers in rice parenchyma cells of 4-FPA-treated plants is associated with a decreased capacity of the white-backed planthopper (WBPH) Sogatella furcifera to reach the plant phloem. We demonstrate that application of 4-PFA in the field enhances rice yield by reducing the abundance of, and damage caused by, insect pests. We demonstrate that 4-FPA also increases the resistance of other major cereals such as wheat and barley to piercing-sucking insect pests. This study unravels a mode of action by which plant strengtheners can suppress herbivores and increase crop yield. We postulate that this represents a conserved defense mechanism of plants against piercing-sucking insect pests, at least in cereals.

The Commonly Used Bactericide Bismerthiazol Promotes Rice Defenses against Herbivores.

Chemical elicitors that enhance plant resistance to pathogens have been extensively studied, however, chemical elicitors that induce plant defenses against insect pests have received little attention. Here, we found that the exogenous application of a commonly used bactericide, bismerthiazol, on rice induced the biosynthesis of constitutive and/or elicited jasmonic acid (JA), jasmonoyl-isoleucine conjugate (JA-Ile), ethylene and H2O2 but not salicylic acid. These activated signaling pathways altered the volatile profile of rice plants. White-backed planthopper (WBPH, Sogatella furcifera) nymphs and gravid females showed a preference for feeding and/or oviposition on control plants: survival rates were better and more eggs were laid than on bismerthiazol-treated plants. Moreover, bismerthiazol treatment also increased both the parasitism rate of WBPH eggs laid on plants in the field by Anagrus nilaparvatae, and also the resistance of rice to the brown planthopper (BPH) Nilaparvata lugens and the striped stem borer (SSB) Chilo suppressalis. These findings suggest that the bactericide bismerthiazol can induce the direct and/or indirect resistance of rice to multiple insect pests, and so can be used as a broad-spectrum chemical elicitor.

Attraction behaviour of Anagrus nilaparvatae to remote lemongrass (Cymbopogon distans) oil and its volatile compounds.

Utilisation of Anagrus nilaparvatae is a promising and effective method for planthoppers manipulation. Twenty-seven components of remote lemongrass (Cymbopogon distans) oil were identified by GC/MS and nine volatiles were selected for behavioural experiments. In this study, we noted that the remote lemongrass oil was attractive to female A. nilaparvatae at concentrations of 0.1 and 1 mg/L. α-Pinene, ß-pinene, eucalyptol, carveol and D-carvone attracted female wasps in the dose-dependent bioassays. Blend 1 (a mixture of eucalyptol, D-carvone, carveol, α-pinene, and ß-pinene with ratios of remote lemongrass oil volatiles of 625:80:11:5:3) attracted female wasps at 10 mg/L, while blend 2 (a mixture of the same five volatiles at the same loading ratio) attracted them at 0.1 and 1 mg/L. These results suggested that plant essential oils could be attractants for natural enemies to control pests. The ratios of volatiles in the mixtures affect the attractiveness of the synthetic mixtures.

Lignocellulose pretreatment in a fungus-cultivating termite.

Depolymerizing lignin, the complex phenolic polymer fortifying plant cell walls, is an essential but challenging starting point for the lignocellulosics industries. The variety of ether- and carbon-carbon interunit linkages produced via radical coupling during lignification limit chemical and biological depolymerization efficiency. In an ancient fungus-cultivating termite system, we reveal unprecedentedly rapid lignin depolymerization and degradation by combining laboratory feeding experiments, lignocellulosic compositional measurements, electron microscopy, 2D-NMR, and thermochemolysis. In a gut transit time of under 3.5 h, in young worker termites, poplar lignin sidechains are extensively cleaved and the polymer is significantly depleted, leaving a residue almost completely devoid of various condensed units that are traditionally recognized to be the most recalcitrant. Subsequently, the fungus-comb microbiome preferentially uses xylose and cleaves polysaccharides, thus facilitating final utilization of easily digestible oligosaccharides by old worker termites. This complementary symbiotic pretreatment process in the fungus-growing termite symbiosis reveals a previously unappreciated natural system for efficient lignocellulose degradation.

Diversity-Oriented Synthesis of Natural-Product-like Libraries Containing a 3-Methylbenzofuran Moiety for the Discovery of New Chemical Elicitors.

Natural products are a major source of biological molecules. The 3-methylfuran scaffold is found in a variety of plant secondary metabolite chemical elicitors that confer host-plant resistance against insect pests. Herein, the diversity-oriented synthesis of a natural-product-like library is reported, in which the 3-methylfuran core is fused in an angular attachment to six common natural product scaffolds-coumarin, chalcone, flavone, flavonol, isoflavone and isoquinolinone. The structural diversity of this library is assessed computationally using cheminformatic analysis. Phenotypic high-throughput screening of ß-glucuronidase activity uncovers several hits. Further in vivo screening confirms that these hits can induce resistance in rice to nymphs of the brown planthopper Nilaparvata lugens. This work validates the combination of diversity-oriented synthesis and high-throughput screening of ß-glucuronidase activity as a strategy for discovering new chemical elicitors.

Laboratory evaluation of differential attraction of Culex pipiens pallens to fruit-based sugar baits.

Mosquito adults usually need to obtain sugar from floral nectaries and damaged fruits/seed pods to replenish their energy reserves. The newly developed attractive toxic sugar baits have been successfully applied in controlling various mosquito species outdoors. However, the attraction of Culex pipiens pallens to different fruit-based sugar baits remains unknown. In the present study, we selected nine common fruit species, prepared the fruit-based sugar solutions, and investigated the attractiveness of different sugar baits to newly emerged Cx. pipiens pallens in the laboratory. The results showed that when tested against the 5% brown sugar solution, all the sugar baits were significantly attractive to both females and males. When tested together in the mesh-covered cage, there was a significant difference on the attractiveness between different fruit-based sugar baits. The most attractive fruit species included Broussonetia papyrifera, Cucumis melo, C. melo var. saccharinus, Amygdalus persica and Pyrus bretschneideri, and their seed pods could be potentially used as ingredients in ATSB for controlling mosquitoes outdoors.

Survivorship and fecundity of Culex pipiens pallens feeding on flowering plants and seed pods with differential preferences.

Adult mosquitoes rely on ingestion of sugar from plants to survive, swarm and mate. Culex pipiens pallens Coguillett is the primary vector of lymphatic filariasis and epidemic encephalitis. Little is known about the effect of feeding on different sugar sources on the survivorship and fecundity of Cx. pipiens pallens. In the present study, newly emerged mosquitoes were exposed to several flowering plant and seed pod species with different olfactory preferences, and the survival times of mosquitoes exposed to these sugar sources were determined. The proportions of mosquitoes that ingested sugar from host plants were investigated by cold anthrone tests. The numbers of eggs per egg raft laid by mosquitoes were compared when they were provided with different sugar sources and one blood meal. The results revealed that feeding on different kinds of sugar sources significantly affected female and male mosquitoes' survival times. Cold anthrone tests indicated that the proportions of sugar-positive mosquitoes from different nutritional regimes within 24h corresponded to the preference rankings of Cx. pipiens pallens to these sugar sources, and rapid declines in the proportions of surviving individuals might be attributed to their insufficient ingestion of sugar from nutritional regimes. Feeding on different sugar sources strongly affected the proportions of engorged mosquitoes, and females that had fed on their preferred sugar sources laid more eggs than mosquitoes provided with less preferred sugar sources. The results would provide insights in developing mosquito control strategies that target the sugar feeding behavior of mosquitoes.