Repellent Activity of Botanical Oils against Asian Citrus Psyllid, Diaphorina citri (Hemiptera: Liviidae)

Insecticide Efficacy of Green Synthesis Silver Nanoparticles on Diaphorina citri Kuwayama (Hemiptera: Liviidae)

Diaphorina citri Kuwayama (Hemiptera: Liviidae) is a vector of Liberibacter asiaticus Jagoueix et al. and Liberibacter americanus Teixeira et al., causal agents of the critical yellow dragon disease or Huanglongbing (HLB), which affects citrus production worldwide. Recently, green synthetic nanoparticles have emerged as a potential alternative to control of agricultural insect pests. The insecticide effect of silver nanoparticles (AgNPs) on 2nd instar nymphs of D. citri under laboratory and greenhouse conditions was evaluated. Mortality was recorded 24, 48, and 72 h after application on D. citri nymphs under both laboratory and greenhouse conditions. The laboratory results showed that AgNPs caused 97.84 and 100% mortality at 32 and 64 ppm, respectively, 72 h after treatment. In the greenhouse, AgNPs caused 78.69 and 80.14% mortality using 64 and 128 ppm 72 h after application. This research is the first to evaluate the green synthesis AgNPs on D. citri and are a promising strategy to control the pest.

Repellent Activity of Clove Essential Oil Volatiles and Development of Nanofiber-Based Dispensers against Pear Psyllids (Hemiptera: Psyllidae)

Pear psyllids are the main vectors of the pathogen 'Candidatus Phytoplasma pyri' causing pear decline. Based on earlier reports, we tested the behavioral activity of the major synthetic compounds of clove essential oil (eugenol, eugenyl acetate, and β-caryophyllene) against Cacopsylla pyri and C. pyricola. Of six mixtures tested in olfactometer assays, a formulation consisting of three specific compounds (M6 mixture) demonstrated a repellent effect on both psyllid species. In addition, this formulation masked the odor of the host Pyrus communis cv. Williams Christ, disturbing the host finding ability of C. pyri. Electrospun fibers were produced with biocompatible polymers poly(ε-caprolactone), cellulose acetate, and solvents formic acid and acetic acid, loaded with the repellent mixture to test their efficacy as dispensers of repellents in laboratory and field. The fibers produced were repellent to C. pyri and effectively masked the odors of pear plants in olfactometer tests. In a pear orchard, we compared the captures of pear psyllids in green-colored attractive traps treated with nanofibers loaded with M6 mixture or unloaded nanofibers (blank). The result showed no differences in the captures of C. pyri between treatments. The release rates of volatiles from the fibers were evaluated weekly over 56 days. The fibers were able to entrap the major compound of the M6 mixture, eugenol, but the release rates were significantly reduced after 21 days. Our results suggest that biodegradable dispensers could be produced with electrospinning, but further improvements are necessary to use repellents as a management tool for pear psyllids in the field.

Cultural Management of Huanglongbing: Current Status and Ongoing Research

Huanglongbing (HLB), formerly known as greening, is a bacterial disease restricted to some Asian and African regions until two decades ago. Nowadays, associated bacteria and their vectors have spread to almost all citrus-producing regions, and it is currently considered the most devastating citrus disease. HLB management can be approached in terms of prevention, limiting or avoiding pathogen and associated vectors to reach an area, or in terms of control, trying to reduce the impact of the disease by adopting different cultural strategies depending on infestation/infection levels. In both cases, control of psyllid populations is currently the best way to stop HLB spread. Best cultural actions (CHMAs, TPS system) to attain this goal and, thus, able to limit HLB spread, and ongoing research in this regard is summarized in this review.

Distribution, Phenology, and Overwintering Survival of Asian Citrus Psyllid (Hemiptera: Liviidae), in Urban and Grove Habitats in North Florida

Cold hardy citrus is an emerging industry in north Florida. However, it is under the threat of Candidatus Liberibacter asiaticus (CLas), the agent of the citrus disease huanglongbing. Distribution and phenology of the Asian citrus psyllid, Diaphorina citri (Kuwayama), the vector of CLas, was investigated over a 2-year sampling period in north Florida. Diaphorina citri was only found in backyard and ornamental citrus along the Gulf of Mexico, and was not observed in cultivated citrus groves during the 2 years (2017-2018) of the survey. Diaphorina citri population peaks occurred approximately 2 mo later than in central Florida with major population peaks occurring in July. The number of D. citri adults was significantly higher on CLas infected than uninfected citrus trees, whereas more nymphs were found on uninfected trees. Most D. citri were negative for CLas except in Franklin county where both infected trees and psyllids were found. We were able to find adult D. citri during all winter months, despite temperatures as low as -5.5°C. During two consecutive winters, we conducted experiments to determine D. citri cold hardiness by caging D. citri under ambient conditions in mid-November and assessing survivors in the following spring. In 2018, approximately 21%, of D. citri adults survived overwintering whereas 16% survived in 2019 despite lower temperature in 2018 than in 2019. As we are at the earliest stage of HLB infestation, management of D. citri and CLas in north Florida should focus on removal of CLas-infected trees to reduce the reservoir of pathogen.

Evaluation of silica nanoparticle mediated delivery of protease inhibitor in tomato plants and its effect on insect pest Helicoverpa armigera

The inert and surface tunable nature of silica nanoparticles (SiNPs) makes them suitable for different applications. We have evaluated the potential of SiNPs for delivering proteins in tomato (Lycopersicon esculentum) plants. SiNPs of 20 and 100 nm (Si20 and Si100) were functionalized with (3-aminopropyl) triethoxysilane (APTES) to obtain Si20APT and Si100APT, respectively, that were non-toxic toward plants. The functionalized nanoparticles were taken up by plants through roots as well as leaf surfaces. They were seen to be localized near the vasculature, particularly around the xylem. Si20APT and Si100APT nanoparticles were conjugated with soybean trypsin inhibitor (STI) to yield Si20APT-STI and Si100APT-STI, respectively. Based on the trypsin inhibitory activity of loaded nanoparticles, optimum loading was obtained for 0.4 mg of STI per 0.8 mg of NPs. Si20APT nanoparticles retained higher contents of STI than Si100APT. Exposure of STI-conjugated nanoparticles to 25°C or pH 8.0 aided release of the inhibitor. The particle bound STI inhibited bovine trypsin by 80% and Helicoverpa armigera gut proteinase (HGP) activity by 50%. Second instar H. armigera larvae ingesting STI-loaded particles (incorporated in artificial diet or leaves) showed significant retardation in growth. In choice assays, Si20APT-STI applied leaf discs were strikingly avoided by insect larvae. On the basis of the results obtained in this investigation, we recommend the use of Si20 nanoparticles for developing plant delivery vehicles in the future.