Volatile Signals From Guava Plants Prime Defense Signaling and Increase Jasmonate-Dependent Herbivore Resistance in Neighboring Citrus Plants.

Intercropping can reduce agricultural pest incidence and represents an important sustainable alternative to conventional pest control methods. Citrus intercropped with guava (Psidium guajava L.) has a lower incidence of Asian citrus psyllid (ACP, Diaphorina citri Kuwayama) and huanglongbing disease (HLB), but the mechanisms are still unknown. In this study, we tested whether volatile organic compounds (VOCs) emitted by guava plants play a role in plant-plant communications and trigger defense responses in sweet orange (Citrus sinensis L. Osbeck) in the laboratory. The results showed that the behavioral preference and developmental performance of ACP on citrus plants that were exposed to guava VOCs were suppressed. The expression of defense-related pathways involved in early signaling, jasmonate (JA) biosynthesis, protease inhibitor (PI), terpenoid, phenylpropanoid, and flavonoid biosynthesis was induced in guava VOC-exposed citrus plants. Headspace analysis revealed that guava plants constitutively emit high levels of (E)-ß-caryophyllene and (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), which can induce the accumulation of JA and promote stronger defense responses of citrus to ACP feeding. In addition, exposure to guava VOCs also increased the indirect defense of citrus by attracting the parasitic wasp Tamarixia radiata. Together, our findings indicate that citrus plants can eavesdrop on the VOC cues emitted by neighboring intact guava plants to boost their JA-dependent anti-herbivore activities. The knowledge gained from this study will provide mechanisms underlying citrus-guava intercropping for the ecological management of insect pests.

Latest Developments in Insect Sex Pheromone Research and Its Application in Agricultural Pest Management.

Since the first identification of the silkworm moth sex pheromone in 1959, significant research has been reported on identifying and unravelling the sex pheromone mechanisms of hundreds of insect species. In the past two decades, the number of research studies on new insect pheromones, pheromone biosynthesis, mode of action, peripheral olfactory and neural mechanisms, and their practical applications in Integrated Pest Management has increased dramatically. An interdisciplinary approach that uses the advances and new techniques in analytical chemistry, chemical ecology, neurophysiology, genetics, and evolutionary and molecular biology has helped us to better understand the pheromone perception mechanisms and its practical application in agricultural pest management. In this review, we present the most recent developments in pheromone research and its application in the past two decades.

Two Alkaloids From Delphinium brunonianum Royle, Their Anti-inflammatory and Anti-oxidative Stress Activity via NF-κB Signaling Pathway.

In this study, we isolated and identified four compounds in Delphinium brunonianum Royle, and they were Delbrunine (1), 4-O-α-D-Glucosyl benzoic acid (2), Kaempferol 3-O-ß-D-glucopyranoside 7-O-α-L-rhamnopyranoside (3) and Eldeline (4). Furthermore, the anti-inflammatory activity of these compounds was screened in RAW264.7 cells. The results showed that the anti-inflammatory activities of compounds 2 and 3 were weak, and 1, 4 had good anti-inflammatory activity. The macrophage inflammation model was established by lipopolysaccharide (LPS). Then, the anti-inflammatory activity was evaluated by ELISA kits, qRT-PCR experiment and western blot experiment. And the anti-oxidative stress activity was assessed by flow cytometry. The results showed that compounds 1, 4 could significantly inhibit the elevation of inflammatory factors nitric oxide (NO), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and also had obvious inhibitory effects on the production of inducible nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX-2). In addition, compounds 1 and 4 could effectively inhibit the overexpression of reactive oxygen species (ROS) in RAW264.7 cells that activated by LPS. These results indicated that compounds 1 and 4 may exert anti-inflammatory and anti-oxidative stress effects through the NF-κB signaling pathway.

Seriphidium brevifolium essential oil: a novel alternative to synthetic insecticides against the dengue vector Aedes albopictus.

The Aedes albopictus mosquito is a vector of several deadly diseases of humans and domesticated animals. Usually, synthetic insecticides are used for mosquito control. The excessive use of synthetic insecticides is hazardous for humans and the environment. Therefore, there is a need to develop environment-friendly and novel mosquito larvicides. In the current study, we evaluated larvicidal and bite protection properties of Seriphidium brevifolium essential oil (SBEO) and its active constituents against this mosquito. SBEO and its active constituents, α, ß-thujone, and limonene, were toxic to A. albopictus, with LC50 values of 21.43, 45.99, 47.38, and 49.46 µg/mL. The cream formulation of EO at 5 % (w/v) provided complete protection against mosquito bites until 70 min after application. Among the EO constituents tested, α and ß-thujone showed considerable protections against mosquito bites but lower as compared with the whole oil. Furthermore, 1:1 combinations of active constituent α-thujone and ß-thujone and 1:1:1 combinations of α-thujone, ß-thujone, and limonene displayed a synergistic effect against the larvae. Particularly, the EO and its active constituents were safer to Poecilia reticulata a mosquito predator, with LC50 ranging from 3934.33 to 14,432.11 µg/mL. Our current study indicated that SBEO and some of its constituents can be used for the control of A. albopictus mosquito, as a novel alternative to hazardous synthetic insecticides and to overcome the problem of increasing insecticides resistance.

Larvicidal, Ovicidal, Synergistic, and Repellent Activities of Sophora alopecuroides and Its Dominant Constituents Against Aedes albopictus.

In the current study, to combat insecticide resistance, we explored larvicidal, ovicidal, synergistic, and repellent activities of Sophora alopecuroides extract and its dominant constituents against Aedes albopictus. The results of the toxicity bioassays demonstrated that the extract of S. alopecuroides exerted significant larvicidal activity (16.66-86.66%) against the third-instar larvae of Ae. albopictus at different concentrations (5-50 ug/mL) and low hatchability of eggs (2.32-75%) at 5-50 ug/mL. The constituents of S. alopecuroides showed a synergistic effect when applied as a mixture (LC30 + LC30) against larvae, while no synergistic effect was observed against the eggs of Ae. albopictus. S. alopecuroides extract provided 93.11% repellency in the first 90 min and gradually decreased to 53.14% after 240 min, while the positive control DEET (N,N-diethyl-3-methylbenzamide) showed 94.18% in the first 90 min and 55.33% after 240 min. All of the results exhibited a concentration-dependent effect. To the best of our knowledge, this is the first time that a study has identified a highly effective extract of S. alopecuroides, which could be used as an alternative agent to control larvae and eggs and to repel adults of Ae. albopictus.

Evaluating the repellent effect of four botanicals against two Bactrocera species on mangoes.

BACKGROUND: Bactrocera dorsalis and B. correcta are economically important fruit fly pests of crops, vegetables, fruits, and nuts worldwide, especially in China. Nowadays in China, B. correcta is a second notorious pest of many fruits after B. dorsalis. Different botanicals have been tested against the B. dorsalis but in the case of B. correcta, no records were published. METHODOLOGY: This study evaluated the repellency of four botanicals (Seriphidium brevifolium, Piper nigrum, Azadirachta indica and quercetin) in acetone dilutions (5%, 2.5% and 1%) against the B. dorsalis and B. correcta at the laboratory conditions (25 ± 2 °C, 60 ± 5% relative humidity, and a photoperiod of L:D 14:10 h). RESULTS: The number of visits after 24-48 h, oviposition punctures, and pupae made by both species were lower on the treated mangoes in comparison to untreated mangoes. S. brevifolium, P. nigrum, A. indica and quercetin have significantly reduced the visits, ovipositional punctures, and pupae of both species. Among botanicals, the P. nigrum was the most effective repellent against B. correcta and as well as B. dorsalis. However, the harmful effects of these botanicals against natural enemies are still unknown.

Differences in susceptibility to insecticides among color morphs of the Asian citrus psyllid.

Insect color morphs are known to vary in detoxification enzyme activity associated with susceptibility to insecticides. Diaphorina citri occurs in three distinct color morphs, and little data are available addressing this question. In this study, susceptibility to nine insecticides was compared among orange/yellow, gray/brown and blue/green morphs of adult D. citri. Imidacloprid and lambda-cyhalothrin resulted in higher mortality in the orange/yellow morph than in the blue/green morph. The orange/yellow morph was significantly more susceptible to acetamiprid, bifenthrin and chlorfenapyr than the blue/green and gray/brown morphs. For clothianidin and chlorpyriphos, the orange/yellow morph was significantly more susceptible than the gray/brown morphs. Susceptibility to dinotefuran and thiamethoxam was not significantly different between the three color morphs of D. citri. Biochemical enzyme assays revealed that the esterase, glutathione S-transferase and cytochrome P450 activities were significantly higher in the gray/brown and blue/green morphs than in the orange/yellow morph; however, the activities of three detoxification enzymes were not significantly different between gray/brown and blue/green morphs. We analyzed the relative expression among the color morphs of six detoxification genes involved in insecticide resistance. GSTS1 and EST-6 were expressed at significantly higher levels in the blue/green morph than in the orange/yellow and gray/brown morphs. The expression levels of CYP4g15, CYP303A1, CYP4C62 and CYP6BD5 were significantly greater in the gray/brown and blue/green morphs than in the orange/yellow morph. These results suggest that insecticide susceptibility in D. citri is associated with color morphs. Detoxification enzyme activity and the relative expression of six detoxification genes may partially explain these differences. These results may facilitate further work to develop a management strategy for control of D. citri.

Development and evaluation of emulsifiable concentrate formulation containing Sophora alopecuroides L. extract for the novel management of Asian citrus psyllid.

Utilization of non-host plants semiochemicals to mediate insect behavior offers a promising opportunity for novel management of insect pests in field crops and fruits. Therefore, there is still a substantial opportunity for the development of natural prophylactic as an eco-friendly approach in the novel pest management programs. Sophora alopecuroides extract has been used as a natural pesticide in the control of agricultural and household pests, but the low persistence effect and rapid biodegradability limit its use on a wider scale in pest management programs. In this study, an emulsifiable concentrate formulation containing S. alopecuroides extract (SAE-EC) was developed with a simple procedure and evaluated for its ovicidal, antifeedant, and repellent effects against Diaphorina citri under laboratory and semi-field conditions. Our results indicated that SAE-EC at 15, 30, and 50 mg/mL concentrations provide complete protection against psyllids for a period of 96 h after application both under laboratory and semi-field conditions, while the aqueous methanolic extract of S. alopecuroides loses its persistence 48 h after application. Furthermore, the emulsifiable concentrate at 20 and 30 mg/mL concentrations, only 15.97% and 31.97% of eggs were able to hatch, and at similar concentrations, 72.86% and 85.5% of honeydew secretion were reduced as compared to the control. SAE-EC at 30 mg/mL concentration has not shown any phytotoxic symptoms on Murraya paniculata seedlings. Fourier transform infrared (FTIR) study revealed the presence of alkaloids in emulsifiable concentrate after 3 months of its preparation placed under ambient temperature. Furthermore, the particle size and polydispersity index (PDI) of the emulsifiable concentrate were also confirmed by dynamic light scattering (DLS). Our finding indicated that emulsifiable concentrate formulation prolongs the persistence of S. alopecuroides extract and enhances its efficacy both under laboratory and semi-field conditions. It has been concluded that the emulsifiable concentrate formulation containing S. alopecuroides extract might be developed as an eco-friendly novel prophylactic against citrus psyllid.

Interference mechanism of Sophora alopecuroides L. alkaloids extract on host finding and selection of the Asian citrus psyllid Diaphorina citri Kuwayama (Hemiptera: Psyllidae).

Manipulating insect behavior through the deployment of semiochemicals offers a promising opportunity for protecting crops in a sustainable manner. Therefore, there is still a significant opportunity for the development of natural crop protectants as eco-friendly tools in pest management. In this context, the aim of the current investigation is to find a novel prophylactic against the Asian citrus psyllid (ACP) and to gain a better understanding of the host-finding and selection ability of the ACP towards Murraya paniculata seedlings treated with Sophora alopecuroides alkaloids extract (SAAE). Our results indicate that foliar application of SAAE influences the psyllid host-finding and selection process. The behavioral assay with M. paniculata seedlings treated with 15 and 30 mg/mL of SAAE, with masked visual cues, revealed that only 6.6 and 10.4% psyllids were able to locate the host in the vials. The results also indicate that citrus psyllids mainly rely on both visual and olfaction in host-finding and selection. In choice settling experiments, psyllids settled almost completely on control seedlings rather than on seedlings treated with SAAE at a concentration of 30 mg/mL. Chemical analyses of the alkaloids extract revealed the presence of sophocarpine (33.90%), sophoridine (6.23%), anagyrine (2.77%), matrine (2.38%), lupanine (1.68%) aphylline (0.89%), and sophoramine (0.75%). In further behavioral bioassays with the dominant alkaloids sophocarpine and sophoridine, the alkaloids repelled ACP at higher concentrations of 50 and 70 mg/mL as compared to SAAE. Furthermore, the 50 mg/mL (1:1, v/v) combination of sophocarpine and sophoridine displayed a synergistic effect and showed the maximum behavioral effect as compared to the individual alkaloid. Based on our results, SAAE makes M. paniculata seedlings unattractive to the psyllids, and therefore, alkaloids could be used in reducing the colonization of citrus plants, subsequently curtailing HLB infection.

Detection and biochemical characterization of insecticide resistance in field populations of Asian citrus psyllid in Guangdong of China.

The Asian citrus psyllid, Diaphorina citri Kuwayama, is one of the most damaging pests of citrus-producing regions throughout the world. The use of insecticides is the main strategy for controlling psyllid and has increased year by year. In this study, four field populations of D. citri were evaluated for resistance to nine different insecticides using the leaf-dip method. The results showed that the highest level of resistance for D. citri was found in imidacloprid with a resistance ratio of 15.12 in the Zengcheng population compared with the laboratory susceptible population. This was followed by chlorpyriphos (6.47), dinotefuran (6.16), thiamethoxam (6.04), lambda-cyhalothrin (4.78), and bifenthrin (4.16). Piperonyl butoxide (PBO) and triphenyl phosphate (TPP) showed significant synergism on imidacloprid effects in the Zengcheng population (3.84- and 2.46-fold, respectively). Nevertheless, diethyl maleate (DEM) had no synergism on imidacloprid. Biochemical enzyme assays suggested that general esterase, glutathione S-transferase and cytochrome P450 monooxygenase activities were higher in the field-collected populations than in the laboratory susceptible population. However, glutathione S-transferase may play a minor role in the resistance of adult D. citri to insecticides. At the molecular level, resistance of D. citri to imidacloprid is mainly related to the increased expression of CYP4C68 and CYP4G70 (>5-fold).