Acaricidal potential of essential oils on Rhipicephalus linnaei: Alternatives and prospects.

The acaricidal potential of various essential oils (EOs) has been evaluated based on their benefits in tick control. This study aimed to investigate the tick-killing activity of Pogostemon cablin "patchouli," Cymbopogon martinii "palmarosa," and Cymbopogon flexuosus "lemongrass" EOs on Rhipicephalus linnaei. Engorged females were collected from domiciled and non-domiciled dogs from Jataí city, Goiás state, to obtain larvae and nymphs in a controlled environment. Two commercial EOs brands were used in this study in different EOs concentrations (2.5, 5, 10, and 20 mg/mL), and was tested by immersion of larvae and nymphs. In the in vitro evaluation of EOs toxicity against R. linnaei larvae, 100 % mortality was achieved with 10 mg/mL of P. cablin oil, whereas mortality rates greater than 98 % were observed with 20 mg/mL of C. martinii and C. flexuosus. In nymphs, high sensitivity was observed, with 100 % mortality achieved using 5 mg/mL of P. cablin and 20 mg/mL of C. martinii and C. flexuosus. The EO of P. cablin "patchouli" demonstrated in vitro toxicity at a lower concentration than the other oils in the two development stages of R. linnaei, and was considered the most efficient and with verified acaricidal activity. Oils of C. martinii "palmarosa" and C. flexuosus "lemongrass" achieved mortality greater than 95 % in larvae and nymphs only at the highest concentration. Therefore, the acaricidal effects of the tested EOs are promising, especially of patchouli oil, which promoted high mortality at a low concentration (LC90 of 2.21 mg/mL).

Neurobehavioral, neurotransmitter and redox modifications in Nauphoeta cinerea under mixed heavy metal (silver and mercury) exposure.

Heavy metals are encountered in nature, and are used in several human endeavors, including in dental fillings. It is well known that the safety of metals depends on their chemical form, as well as the dose and route through which biological systems are exposed to them. Here, we used the Nauphoeta cinerea model to examine the mechanism by which salts of the heavy metals used in dental fillings - silver and mercury - exert their neurotoxicity. Nymphs exposed to heavy metals presented with reduced motor and exploratory abilities as they spent more time immobile, especially in the periphery of a novel object, and covered less distance compared with control nymphs. Exposure to AgNO3 and HgCl2 also exacerbated levels of oxidative stress markers (MDA & ROS) and the neurotransmitter regulators - AChE and MAO, while reducing antioxidant activity markers, both in biochemical (thiol & GST) and RT-qPCR (TRX, GST, SOD, Catalase) examinations, in neural tissues of the cockroach. The observed disruptions in neurolocomotor control, synaptic transmission and redox balance explain how heavy metal salts may predispose organisms to neurological disorders.

Toxicological assessment of cadmium exposure through Hyphantria cunea larvae on the predation fitness of Arma chinensis.

Heavy metals are defined as an abiotic factor that affects the efficiency of biological pest control. This study constructed a cadmium (Cd)-polluted artificial diets-Hyphantria cunea-Arma chinensis food chain to analyze the effects of Cd exposure on the ability of A. chinensis to control H. cunea. The results revealed that Cd was transferred through the artificial diet to H. cunea larvae and A. chinensis nymphs via a biological amplification effect. After feeding on Cd-accumulated H. cunea larvae, the body weight of A. chinensis nymphs reduced, mortality increased, developmental duration prolonged, and the expression of growth regulatory genes (EX, cycE, and MER) decreased. Cd activated the antioxidant defense system of the nymphs, accompanied by a significant enhancement in the contents of H2O2 and MDA, marked damage to the midgut sub-microstructure, and a remarkable induction in the expression of genes crucial for the mitochondrial pathway/ER stress-apoptosis pathway. Cd significantly diminished the contents of total amino acids, glucose, free fatty acids, and expression of the genes (HK2, PFK, IDH1, and IDH2) essential for the TCA cycle and glycolysis in the nymphs. The preference of the A. chinensis nymphs to Cd-treated H. cunea larvae was evidently reduced. Cd diminished the search-ability, food intake, instantaneous attack rate, and maximum theoretical daily food intake but prolonged the feeding time of the nymphs. Taken together, Cd exposure reduces the ability of A. chinensis nymphs to control H. cunea and provides a new challenge for the efficiency of insect pest control using natural enemies. These findings have important reference value for optimizing pest control strategies in heavy metal polluted areas.

Comparative analysis of essential oil efficacy against the Asian longhorned tick Haemaphysalis longicornis (Acari: Ixodidae).

This study evaluated the potential repellent and acaricidal effects of 4 essential oils (clove, eucalyptus, lavender, and mint) against the Asian longhorned tick Haemaphysalis longicornis, a vector of various tick-borne diseases in medical and veterinary contexts. Selected for their potential repellent and acaricidal properties, the 4 essential oils were tested on adult and nymph H. longicornis ticks at different concentrations. The experiment assessed mortality rates and repellency, particularly during tick attachment to host skin. There was a significant increase (p<0.05) in tick mortality and repellency scores across all groups. At a 1% concentration, adult tick mortality ranged from 36% to 86%, while nymph mortality ranged from 6% to 97%. Clove oil exhibited notable efficacy, demonstrating high mortality rates of nymphs and adults. Clove oil also displayed strong repellency properties, with a repellency index of 0.05, surpassing those of mint, eucalyptus, and lavender oils. Clove oil showed the highest effectiveness in deterring nonattached adult ticks (90%) and nymphs (95%) when applied to skin. Clove oil was the most effective against adult and nymph ticks, achieving mortality rates of 86% and 97%, respectively, and led to the highest nonattachment rates when applied to skin. In conclusion, essential oils such as clove, eucalyptus, lavender, and mint oils present promising results for tick population control.

Various functions of detoxification enzymes against insecticides in Nilaparvata lugens selected by toxicity assays and RNAi methods.

The brown planthopper (BPH), Nilaparvata lugens is a devastating agricultural pest of rice, and they have developed resistance to many pesticides. In this study, we assessed the response of BPH nymphs to nitenpyram, imidacloprid, and etofenprox using contact and dietary bioassays, and investigated the underlying functional diversities of BPH glutathione-S-transferase (GST), carboxylesterase (CarE) and cytochrome P450 monooxygenase (P450) against these insecticides. Both contact and ingestion toxicity of nitenpyram to BPH were significantly higher than either imidacloprid or etofenprox. Under the LC50 concentration of each insecticide, they triggered a distinct response for GST, CarE, and P450 activities, and each insecticide induced at least one detoxification enzyme activity. These insecticides almost inhibited the expression of all tested GST, CarE, and P450 genes in contact bioassays but induced the transcriptional levels of these genes in dietary bioassays. Silencing of NlGSTD2 expression had the greatest effect on BPH sensitivity to nitenpyram in contact test and imidacloprid in dietary test. The sensitivities of BPH to insecticide increased the most in the contact test was etofenprox after silencing of NlCE, while the dietary test was nitenpyram. Knockdown of NlCYP408A1 resulted in BPH sensitivities to insecticide increasing the most in the contact test was nitenpyram, while the dietary test was imidacloprid. Taken together, these findings reveal that NlGSTD2, NlCE, and NlCYP408A1 play an indispensable role in the detoxification of the contact and ingestion toxicities of different types of insecticides to BPH, which is of great significance for the development of new strategies for the sucking pest control.

The sublethal concentration of acetamiprid suppresses the population growth of 2 species of wheat aphids, Sitobion miscanthi and Schizaphis graminum (Hemiptera: Aphididae).

Sitobion miscanthi and Schizaphis graminum (Rondani) are the 2 main aphid species that occur simultaneously, causing significant loss to wheat production. Acetamiprid has been used to control a variety of pests, including aphids. In this study, the sublethal effect of acetamiprid on S. miscanthi and S. graminum was evaluated using life-table analyses. The results showed that acetamiprid has a high toxicity to S. miscanthi and S. graminum with a LC50 of 1.90 and 3.58 mg/L at 24 h, respectively. The adult longevity and fecundity of S. miscanthi and S. graminum F0 generation were significantly reduced after being exposed to a sublethal concentration of acetamiprid. Additionally, the sublethal concentration of acetamiprid had negative transgenerational effects on S. miscanthi and S. graminum, which showed a significant decrease in fecundity and population life-table parameters involving age-stage-specific survival rate (sxj), age-specific survival rate (lx), and intrinsic rate of increase (r). Furthermore, the population projections showed that the total population size of S. miscanthi and S. graminum was significantly lower in the aphid group exposed to sublethal concentration of acetamiprid compared to the control group. These results suggest that sublethal concentration of acetamiprid suppresses the population growth of S. miscanthi and S. graminum. This finding is beneficial to the control of wheat aphids, and is important to fully understand the role of acetamiprid in integrated pest management.

Reduced effectiveness of permethrin-treated military uniforms after prolonged wear measured by contact irritancy and toxicity bioassays with Ixodes scapularis (Acari: Ixodidae) nymphs.

Factory-treated permethrin uniforms are the primary method used by the US Army to prevent arthropod bites and transmission of arthropod-borne diseases. In this study previously worn uniforms were collected from cadets at the United States Military Academy in West Point, NY to determine the amount of permethrin remaining after prolonged wear and subsequent effects on ticks. Six trousers were collected from cadets in the sophomore, junior, and senior classes. A new, unwashed uniform served as a positive control and an untreated maternity uniform served as a negative control. Fabric samples were removed from each trouser and used in bioassays with laboratory-reared Ixodes scapularis Say nymphs. Contact irritancy bioassays measured the nymphs' ability to remain in contact with fabric for a period of 5 min. Toxicity bioassays measured tick survival at 1 and 24 h after contacting uniform samples. liquid chromatography-mass spectrometry was used to quantify the permethrin content (mg/cm2) in each uniform after the bioassays were complete. The results showed significant amounts of permethrin were lost after extended wear and it was related to the cadet year group. The contact irritancy assays found uniforms with less permethrin did not irritate ticks and cause them to dislodge. Mortality was also affected by permethrin levels, with less ticks dying at 24 h on older uniforms. The results from this study show older uniforms lose most of their permethrin and no longer provide the same levels of protection.

Effects of chlorantraniliprole on the development, fecundity and prey consumption of a non-specific predator, Rhynocoris fuscipes (Hemiptera: Reduviidae).

Transplant treatment with chlorantraniliprole (CAP) is a proactive approach to protect transplanted plants from pests during early establishment and has been comprehensively applied in tobacco fields in Guangdong Province, China. However, it is not known whether the high dose of CAP in transplant treatments has lethal or sublethal effects on the generalist predator Rhynocoris fuscipes Fabricius (Hemiptera: Reduviidae). To address this concern, the mortalities of R. fuscipes were assessed when 2nd instar larvae of R. fuscipes were in direct contact with or consuming CAP and when their eggs were exposed to CAP. Furthermore, 2nd instar nymphs R. fuscipes were long-term exposed to CAP until they reached adulthood, and their life table parameters were determined. After exposure to CAP, the activity of detoxification enzymes (P450, CaeE and GST) and the functional respond of R. fuscipes to their preys Agrotis ipsilon larvae were determined. In this study, CAP at all concentrations did not significantly increase the mortality of 2nd instar of R. fuscipes nymphs in comparison with the control. The detoxification enzyme (P450, CarE and GST) activities and the number of A. ipsilon larvae consumed by R. fuscipes in the transplant treatment were not affected by CAP after 3-d or long-term exposure. These results indicated that CAP was harmless to R. fuscipes according to IOBC protocols. However, during the treatment of 2nd instar nymphs with a label rate of 15 g AI/ha and a 5× label rate of 75 g AI/ha, CAP significantly prolonged the pre-adult and pre-oviposition periods, and treated adults had lower oviposition. Attention should be given to the time interval between transplant treatment and the release of this biocontrol agent into the field to minimize the impact of CAP on the predator R. fuscipes.

Insecticidal activity of fluralaner (Exzolt®) administered to Gallus gallus domesticus against triatomines (Hemiptera, Reduviidae, Triatominae).

BACKGROUND: Triatoma infestans, Triatoma brasiliensis, Triatoma pseudomaculata and Rhodnius prolixus are vectors of Trypanosoma cruzi, the etiological agent of Chagas disease. Chickens serve as an important blood food source for triatomines. This study aimed to assess the insecticidal activity of fluralaner (Exzolt®) administered to chickens against triatomines (R. prolixus, T. infestans, T. brasiliensis and T. pseudomaculata). METHODS: Twelve non-breed chickens (Gallus gallus domesticus) were randomized based on weight into three groups: negative control (n = 4); a single dose of 0.5 mg/kg fluralaner (Exzolt®) (n = 4); two doses of 0.5 mg/kg fluralaner (Exzolt®) (n = 4). Nymphs of 3rd, 4th and 5th instars of R. prolixus, T. infestans, T. brasiliensis and T. pseudomaculata (all n = 10) were allowed to feed on chickens before treatment, and at intervals of 1, 7, 14, 21, 28, 35 and 56 days after treatment, with insect mortality determined. RESULTS: Treatment with two doses of fluralaner showed higher insecticidal efficacy against R. prolixus, T. infestans and T. brasiliensis compared to the single-dose treatment. Similar insecticidal efficacy was observed for T. pseudomaculata for one and two doses of fluralaner. Insecticidal activity of fluralaner (Exzolt®) against triatomine bugs was noted up to 21 and 28 days after treatment with one and two doses of fluralaner, respectively. CONCLUSIONS: The results demonstrate that treatment of chickens with fluralaner (Exzolt®) induces insecticidal activity against triatomines for up to 28 days post-treatment, suggesting its potential use as a control strategy for Chagas disease in endemic areas.

Repellent activity of essential oils to the Lone Star tick, Amblyomma americanum.

BACKGROUND: The Lone Star tick, Amblyomma americanum is important to human health because of a variety of pathogenic organisms transmitted to humans during feeding events, which underscores the need to identify novel approaches to prevent tick bites. Thus, the goal of this study was to test natural and synthetic molecules for repellent activity against ticks in spatial, contact and human fingertip bioassays. METHODS: The efficacy of essential oils and naturally derived compounds as repellents to Am. americanum nymphs was compared in three different bioassays: contact, spatial and fingertip repellent bioassays. RESULTS: Concentration response curves after contact exposure to 1R-trans-chrysanthemic acid (TCA) indicated a 5.6 µg/cm2 concentration required to repel 50% of ticks (RC50), which was five- and sevenfold more active than DEET and nootkatone, respectively. For contact repellency, the rank order of repellency at 50 µg/cm2 for natural oils was clove > geranium > oregano > cedarwood > thyme > amyris > patchouli > citronella > juniper berry > peppermint > cassia. For spatial bioassays, TCA was approximately twofold more active than DEET and nootkatone at 50 µg/cm2 but was not significantly different at 10 µg/cm2. In spatial assays, thyme and cassia were the most active compounds tested with 100% and 80% ticks repelled within 15 min of exposure respectively and was approximately twofold more effective than DEET at the same concentration. To translate these non-host assays to efficacy when used on the human host, we quantified repellency using a finger-climbing assay. TCA, nootkatone and DEET were equally effective in the fingertip assay, and patchouli oil was the only natural oil that significantly repelled ticks. CONCLUSIONS: The differences in repellent potency based on the assay type suggests that the ability to discover active tick repellents suitable for development may be more complicated than with other arthropod species; furthermore, the field delivery mechanism must be considered early in development to ensure translation to field efficacy. TCA, which is naturally derived, is a promising candidate for a tick repellent that has comparable repellency to commercialized tick repellents.

Chemical symphony: Unraveling triatomine aggregation and attraction patterns for innovative pest control solutions.

Aggregation is a spatial distribution pattern where individuals can be grouped through interaction with particular signals or cues [e.g., chemical substances]. Numerous triatomine species exhibit attraction and aggregation around both conspecific and heterospecific feces. It remains unclear whether compounds released by feces function as signals (pheromones or synomones) or cues. Employing a bioassay that mimics field conditions, we investigated the response of Triatoma pallidipennis bugs to volatiles present in its feces and blends of these compounds. Our findings indicate that short-chain aldehydes, namely nonanal, octanal, heptanal, and hexanal, attract fifth-instar nymphs. Furthermore, insects responded to individual compounds as well as secondary, ternary, and quaternary blends. The most attractive blend consisted of all four aldehydes. Additionally, quaternary blends at various compound ratios attracted fifth-instar nymphs of T. phyllosoma and T. longipennis. We discuss the potential roles of these compounds as signals or cues and explore their application as bait in control programs.

Encapsulation of carvacrol and thymol with yeast cell wall and its repellent activity against Amblyomma sculptum and Rhipicephalus sanguineus (Sensu Lato).

The main way to avoid contact with ticks and consequently tick-borne disease is the use of synthetic repellents. The search of new repellent compounds to increase the possibilities of use in strategies controls are necessary. The present study evaluated the repellent activity of two natural terpenes carvacrol and thymol in each one two different formulation (encapsulated and nonencapsulated with yeast cell wall) against the ticks Amblyomma sculptum and Rhipicephalus sanguineus sensu lato nymphs. Nymphs of A. sculptum and R. sanguineus s.l. of a single generation were used. The vertical filter paper repellency assay were performed with different concentration of both terpenes encapsulated and nonencapsulated in yeast cell wall. The repellent concentration 50% (RC50) were calculated to each compound formulation. Both carvacrol and thymol (encapsulated and nonencapsulated), had a repellent activity against A. sculptum and R. sanguineus s.l nymphs. Amblyomma sculptum was more sensitive to nonencapsulated carvacrol (RC50 values: 0.0032 to 0.0082 mg/cm2 after 1 and 15 min) (P < 0.05), while R. sanguineus s.l. was more sensitive to encapsulated carvacrol (RC50 values: 0.00008 to 0.0035 mg/cm2 after 1 and 15 min) (P < 0.05). Among tick species, R. sanguineus s.l. was more sensitive for most compounds than A. sculptum (P < 0.05). Although with distinct repellent activities, carvacrol and thymol encapsulated can be a promising alternative to synthetic repellents against A. sculptum and R. sanguineus s.l.

Wettable sulphur application for Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) management: laboratory and semi-field experiments.

BACKGROUND: The brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), is a significant threat to crop production. Alternatives to synthetic pesticides are needed for its management. Here we investigated the effect of sulphur on H. halys. Experiments were performed to evaluate both mortality and deterrence/repellence of H. halys following sulphur treatments in laboratory and semi-field conditions. RESULTS: Brown marmorated stink bug mortality was not influenced by sulphur applications. However, in two-choice experiments in insect cages and olfactometer, more H. halys adults moved toward the untreated control rather than the sulphur-treated food sources, with a high effect as the concentration increased. A semi-field experiment using potted apple plants confirmed the results observed in the laboratory, showing a deterrent and/or repellent effect of sulphur-based products on H. halys. CONCLUSIONS: Sulphur applications were associated with a deterrent/repellent effect on the brown marmorated stink bug. The use of sulphur-based products could represent a promising tool for Integrated Pest Management strategies against H. halys in fruit crops. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Exogenous ABA promotes resistance to Sitobion avenae (Fabricius) in rice seedlings.

BACKGROUND: Over the course of evolution, plants have developed various sophisticated defense mechanisms to resist pests and diseases. The phytohormone abscisic acid (ABA) has an important role in the growth and development of plants and confers tolerance to selected abiotic stressors, such as drought. Previous studies have shown that ABA promotes the deposit of callose in response to piercing/sucking insect pests. The English grain aphid, Sitobion avenae Fabricius, causes huge losses in rice and is especially harmful to rice seedlings. RESULTS: Exogenous ABA promoted growth and reduced the feeding behavior of S. avenae nymphs in rice. Our results suggested that enhanced trichome density and increased expression of related genes may be associated with rice resistance to aphids. An analysis of volatiles revealed the production of seven compounds associated with pest resistance. CONCLUSION: These results indicate that ABA reduces aphid feeding in rice. Our findings provide a basis for understanding ABA-mediated defense responses in rice and provide insights on more environmentally-friendly approaches to control. © 2024 Society of Chemical Industry.

Effects of thiamethoxam on physiological and molecular responses to potato plant (Solanum tuberosum), green peach aphid (Myzus persicae), and parasitoid (Aphidius gifuensis).

BACKGROUND: To improve integrated pest management (IPM) performance it is essential to assess pesticide side effects on host plants, insect pests, and natural enemies. The green peach aphid (Myzus persicae Sulzer) is a major insect pest that attacks various crops. Aphidius gifuensis is an essential natural enemy of M. persicae that has been applied effectively in controlling M. persicae. Thiamethoxam is a neonicotinoid pesticide widely used against insect pests. RESULTS: The current study showed the effect of thiamethoxam against Solanum tuberosum, M. persicae, and A. gefiuensis and the physiological and molecular response of the plants, aphids, and parasitoids after thiamethoxam application. Thiamethoxam affected the physical parameters of S. tuberosum and generated a variety of sublethal effects on M. persicae and A. gefiuensis, including nymph development time, adult longevity, and fertility. Our results showed that different thiamethoxam concentrations [0.1, 0.5, and 0.9 µm active ingredient (a.i.)/L] on different time durations (2, 6, and 10 days) increased the antioxidant enzyme activities SOD, POD, and CAT of S. tuberosum, M. persicae, and A. gefiuensis significantly compared with the control. Our results also showed that different thiamethoxam concentrations (0.1, 0.5, and 0.9 µm a.i./L) on different time durations (2, 6, and 10 days) increased the expression of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), acetylcholinesterase (AChE), carboxylesterase (CarE) and glutathione-S-transferase (GST) genes of S. tuberosum, M. persicae, and A. gefiuensis compared with the control. CONCLUSION: Our findings reveal that using thiamethoxam at suitable concentrations and time durations for host plants and natural enemies may enhance natural control through the conservation of natural enemies by overcoming any fitness disadvantages. © 2024 Society of Chemical Industry.

Effects of solid and aqueous dietary diflubenzuron ingestion on some biological parameters in synthetic pyrethroid-resistant German cockroach, Blattella germanica L. (Blattodea: Ectobiidae).

Cockroaches, widespread pests found in metropolitan areas, are known as vectors of various disease agents, including viruses, fungi and antibiotic-resistant bacteria, as well as causing allergies in humans. Insect growth regulators have been used in pest management for several decades. These insecticides disrupt insect development and reproduction. Chitin synthesis inhibitors interfere with chitin biosynthesis in insects, causing abortive moulting and mortality, as well as inhibiting egg fertility, and larval hatching in insects. In this research, we evaluated the various effects of diflubenzuron, a chitin synthesis inhibitor, on synthetic pyrethroid-resistant German cockroach (Blattella germanica L. Blattodea: Ectobiidae), including ootheca production, oothecal viability, ootheca incubation time, the number of nymphs emerging from the ootheca and survivorship of nymphs. The cockroaches were fed diets that contained diflubenzuron, which was added to solid bait (impregnated fish food) and ingestible aqueous bait (impregnated cotton). Three concentrations (0.5%, 1% and 2%) were used in the experiments. As a result, diflubenzuron treatment led to ootheca production ranging from 60% to 100%; statistically, no difference was found between the treatment and the control groups. The number of nymphs emerging from the first and second ootheca was reduced by 40%-100% in the diflubenzuron-treated groups compared with the control. Nymphs exposed to diflubenzuron-impregnated solid bait and ingestible aqueous bait experienced mortality exceeding 92.1% and 66.27% within 15 days, respectively. In conclusion, diflubenzuron is a potential insecticide for use in cockroach baits to control B. germanica, as it caused high nymphal and embryonic mortality in the synthetic pyrethroid-resistant population and decreased the number of nymphs emerging from the ootheca.

Repellent effects of Chinese cinnamon oil on nymphal ticks of Haemaphysalis longicornis, Rhipicephalus haemaphysaloides, and Hyalomma asiaticum.

The repellent activity of Chinese cinnamon oil (Cinnamomum cassia) on nymphal ticks (Haemaphysalis longicornis Neumann, Rhipicephalus haemaphysaloides Supino, and Hyalomma asiaticum Schulze and Schlottke) was evaluated in a sample Y-tube bioassay. The results were based on the vertical migration of ticks during the host-seek phase and showed a dose-dependent repellent effect of Chinese cinnamon oil on the tested nymphs after 6 h. For H. longicornis, R. haemaphysaloides, and H. asiaticum at the concentrations (vol/vol) of 3, 3, and 1.5%, the repellent percentages over time were 68-97, 69-94, and 69-93%, respectively, which indicated strong repellent activities against ticks, similar to the positive control DEET (N,N-diethyl-3-methylbenzamide). Chinese cinnamon oil exerted the strongest effect on H. asiaticum nymphs. To our knowledge, this is the first study to investigate the repellent effects of Chinese cinnamon oil on ticks. Chinese cinnamon oil has considerable potential and should be developed as a practical tick repellent.

Persistence Enhancement of a Promising Tick Repellent, Benzyl Isothiocyanate, by Yeast Microcarriers.

Phenethyl isothiocyanate isolated from Armoracia rusticana root oil and its derivatives were tested at different doses in a bioassay designed to evaluate repellency against individual Haemaphysalis longicornis nymphs. Among the tested compounds, benzyl isothiocyanate exhibited repellency against H. longicornis nymphs at the lowest dose of 0.00625 mg/cm2, followed by phenethyl isothiocyanate (0.0125 mg/cm2) and phenyl isothiocyanate (0.025 mg/cm2). The behavioral responses of H. longicornis nymphs exposed to benzyl isothiocyanate and phenethyl isothiocyanate indicated that the mode of action of these compounds can be mainly attributed to the vapor phase. Encapsulated benzyl isothiocyanate showed repellency up to 120 min post-application at 0.1 mg/cm2, whereas pure benzyl isothiocyanate showed repellency up to 60 min post-application at 0.1 mg/cm2. The present study suggests that benzyl isothiocyanate is a potential repellent for protection against H. longicornis nymphs, and encapsulation in yeast cells may enhance the repellency effect.

Ovicidal activity of spirotetramat and its effect on hatching, development and formation of Frankliniella occidentalis egg.

Frankliniella occidentalis (Pergande) has become an important vegetable pest worldwide because of its economic damage to crop production. However, it is difficult to control due to its unique living habits. In this study, the eggs of F. occidentalis were used as the target to explore the ovicidal activity of spirotetramat on the thrips and its effect on hatching, development and formation. After the treatment of spirotetramat, the LC50 value descreased with increased egg age using egg dipping method, and showed the same trend as the leaf dipping method verified on living plants. Through ultra-depth-of-field microscopy, scanning electron microscopy and transmission electron microscopy, the egg shell and internal structures of F. occidentalis eggs were studied. Spirotetramat can destroy the egg shells of F. occidentalis, resulting in shrinkage of the egg surface, sunken pores, egg deformities, egg shell rupture and other phenomena. This allows spirotetramat to enter the egg and destroy the egg structure, making the egg internal structure flocculent, fuzzy and unevenly distributed, which affects embryonic development and causes the nymphs to die before hatching. Therefore, the prevention and control of F. occidentalis using spirotetramat before damage is caused to crops should have a better effect.

Insecticidal efficacy of fluralaner (Bravecto®) against Triatoma brasiliensis, a major vector of Trypanosoma cruzi in Brazil.

BACKGROUND: Triatomines are responsible for the vector transmission of the protozoan parasite Trypanosoma cruzi, which causes Chagas disease. Triatoma brasiliensis is the main vector of the parasite in Brazil, and dogs are an important reservoir of the parasite. The aim of this study was to evaluate the insecticidal effect of fluralaner (Bravecto®) on T. brasiliensis after a blood meal in treated dogs. METHODS: Healthy mongrel dogs (n = 8) were recruited from the Zoonoses Control Center (ZCC) in the city of Natal, Rio Grande do Norte, Brazil, and randomized into two groups, a fluralaner (Bravecto®)-treated group (n = 4) and a control group (n = 4). Colony-reared third-, fourth- and fifth-instar nymphs of T. brasiliensis nymphs (n = 10) were allowed to feed on dogs from both groups for 30-40 min, once monthly, for up to 12 months. Bug mortality was observed up to 5 days after each blood meal. RESULTS: Mortality in triatomines which had a blood meal on fluralaner (Bravecto®)-treated dogs was 100% for up to 7 months after treatment, with mortality decreasing to 66.4% after 8 months, 57% after 9 months, 35% after 10 months, 10% after 11 months and 0% after 12 months. The mortality of triatomines that fed on non-treated control dogs was always ≤ 2.5%. CONCLUSIONS: Our results suggest that fluralaner (Bravecto®) treatment of dogs induces long-term mortality of T. brasiliensis after the blood meal. This is a potential approach to be used to control vector transmission of T. cruzi, the etiological agent of Chagas disease, especially in endemic areas.