Acaricide Application Research Articles

Laboratory assays on the effects of a novel acaricide, SYP-9625 on Tetranychus cinnabarinus (Boisduval) and its natural enemy, Neoseiulus californicus (McGregor).

ObjectiveTetranychus cinnabarinus (Boisduval) is an agricultural mite pest threatens crops throughout the world, causing serious economic loses. Exploring the effects of acaricides on predatory mites is crucial for the combination of biological and chemical control of T. cinnabarinus. Neoseiulus californicus (McGregor) is one of the principal natural enemies of T. cinnabarinus, which can be applied in protected agriculture. In this study, the effects of sublethal concentrations of a new acaricide, SYP-9625 on two mite species, and the effects of the application concentration on predatory mite, N. californicus were assessed. The aim of the present study was to evaluate the effect of SYP-9625 on life parameters and predation capacity of N. californicus based on the concentration-response bioassay of T. cinnabarinus to explor the application of the new acaricide with natural enemy N. californicus.MethodAll of the experiments were conducted under laboratory conditions [25 ± 1°C, 16: 8 h (L: D) and 75 ± 5% RH]. The sublethal concentrations LC10 (0.375μg/mL) and the LC30 (0.841μg/mL) against T. cinnabarinus and the application concentration (100μg/mL) against N. californicus were used to evaluate the effects of SYP-9625 on population parameters of N. californicus based on an age-stage, two-sex life table and its predation capacity by functional response.Resultcinnabarinus females treated with LC30 exhibited significantly reduced net reproductive rates (R0 = 11.02) in their offspring compared with females treated with LC10 (R0 = 14.96) and untreated females (R0 = 32.74). However, the intrinsic rate of increase (rm) and the finite rate of increase (λ) of N. californicus indicated that the application concentration of SYP-9625 had no significant negative effect on N. californicus eggs (rm = 0.277, λ = 1.319) compared to the control (rm = 0.292, λ = 1.338). Additionally, most population parameters of N. californicus showed a dose-dependent manner with the increase of the concentration of SYP-9625 against T. cinnabarinus. SYP-9625 also stimulated the control efficiency of N. californicus against immobile stages including eggs and larvae.ConclusionThis study demonstrated that sublethal concentrations of SYP-9625 can inhibit the population growth of T. cinnabarinus. In addition, the sublethal concentrations and the application concentration showed no effect on the population growth of N. californicus. These two advantages described above showed great commercial potential of this new acaricide based on population parameters of the two mite species and predation capacity of the predatory mite under laboratory conditions.

Spraying pyrethroid and neonicotinoid insecticides can induce outbreaks of Panonychus citri (Trombidiformes: Tetranychidae) in citrus groves.

Panonychus citri (McGregor) (Trombidiformes: Tetranychidae) is one of the main defoliator mites in citrus groves. In Brazil, P. citri was formerly considered a secondary pest, but in recent years, the population levels of this mite have increased in many groves, requiring additional acaricide applications for its control. The population growth of P. citri is associated with the increase in the number of applications of pyrethroid and neonicotinoid insecticides to control insect citrus pests. This study assessed the effects of pyrethroid (deltamethrin, esfenvalerate, λ-cyhalothrin) and neonicotinoid (imidacloprid and thiamethoxam) insecticides on biological, behavioral and demographic parameters of P. citri. None of the insecticides tested affected larval hatching, but deltamethrin, esfenvalerate, and λ-cyhalothrin reduced the survival of larvae and protonymphs. Deltamethrin, esfenvalerate, and λ-cyhalothrin induced a significant increase in the fecundity of surviving females. Pyrethroids also caused repellency and changed feeding and oviposition preferences. In contrast, imidacloprid and thiamethoxam did not affect the survival of immature stages, but imidacloprid significantly increased fecundity. Imidacloprid and thiamethoxam did not cause any repellent effect or changes in the feeding and oviposition preferences. Based on the demographic parameters, deltamethrin, λ-cyhalothrin, and imidacloprid increased Ro, r, and λ, whereas esfenvalerate and thiamethoxam were similar to the control. Therefore, the use of these insecticides (especially deltamethrin, λ-cyhalothrin, and imidacloprid) requires caution, such as avoiding repeated use of these compounds during the periods of P. citri incidence in citrus groves.

Multiple acaricide resistance and underlying mechanisms in Tetranychus urticae on hops

The polyphagous pest Tetranychus urticae feeds on over 1100 plant species including highly valued economic crops such as hops (Humulus lupulus). In the key hop production region of the Pacific Northwest of the USA, T. urticae is one of the major arthropod pests. Over the years, T. urticae control has been dominated by the application of various acaricides. However, T. urticae quickly adapts to these acaricides by developing resistance. Here, we determined resistance ratios of T. urticae populations in hops to three acaricides: etoxazole, fenpyroximate, and spirodiclofen. The mechanisms underlying resistance to these and three other acaricides were investigated in 37 field-collected T. urticae populations using a comprehensive diagnostic approach. Our data showed that T. urticae populations exhibited complex adaptation patterns to acaricides. Resistance to abamectin, fenpyroximate, and spirodiclofen by enhanced target metabolic detoxification gene(s) was identified in 100%, 50%, and 20% of populations tested, respectively. Resistance to bifenthrin, bifenazate, and etoxazole by target site insensitivity was pervasive among tested populations. Our study provides new information in understanding the complexity of T. urticae adaptation to multiple acaricides, which will help in designing sustainable pest control strategies for T. urticae on hops and other economically valuable crops.

Tick infestations and gastrointestinal helminthosis among goats and cattle at abattoirs in Abakaliki Metropolis, Ebonyi State, Nigeria

Parasitism and parasitosis constitute serious animal health problems that predispose them to other more serious health conditions. Such conditions can reduce their productivity and marketability, thereby reducing their economic values. A total of 126 livestock comprising 63 goats and 63 cattle from abattoirs in Abakaliki Metropolis were subjected to ectoparasitic and gastrointestinal parasitic examinations, using approved standard diagnostic parasitological techniques. The recovered parasites were identified with standard identification guides. Rhipicephalus sanguineus and R. microplus were the two recovered ectoparasites from both groups of animal. There was no significant difference (p = 0.0859) in the prevalence of the tick species between the animals. Dictyocaulus species was the most abundant gastrointestinal helminth infecting both goats and cattle. There was no complete dominance of parasite species infecting the two groups of animal but the Shannon-Weiner diversity index indicated high parasite diversity for both goats and cattle. Periodic application of efficacious acaricides mixed (sequential) grazing and regular deworming with the use of strategic broad spectrum chemotherapeutic anthelmintics are strongly recommended. Keywords : Cattle; goats; helminthes; infestations; tick.

Prevalence and species composition of major internal and external parasites of calves in selected dairy farms of Bahir Dar milk-shade

This study was carried out from October 2013 to November 2014 in selected dairy farms of Bahir Dar milk-shade to estimate the prevalence and species composition of major internal and external parasites and to examine the associated risk factors in dairy calves. A total of 168 and 77 dairy calves less than 9 month old were used to study the prevalence of calf internal and external parasites, respectively. Type of internal and external parasites, degree of nematode infection (EPG) and packed cell volume (PCV) were determined by using standard parasitological and hematological procedures. The overall prevalence of internal and external parasites was 65.5% and 45%, respectively. The prevalence of Coccidia, Strongyle spp, Ascaris, Monezia, Paramphistomum, Trichuris, Schistosoma and Fasciola spp. was 25.6%, 20.8%, 17.1%, 14.3%, 6.0%, 3.0%, 1.8% and 0.6%, respectively. A significant difference (p<0.05) was observed in strongyle and coccidia infection across season and dairy production system. Major external parasites of calves were ticks (23.4%), flea (16.9%) and lice (7.8%). Boophilus decoloratus (17.1%), Amblyoma varigatum (2.6%) and Rhipicephalus evertsi-evertsi, (2.6%) were the prevailed tick species found in the study area. The prevalence of B. decoloratus was significantly (p<0.05) higher in peri-urban (26.8%) than urban (5.6%) dairy. Ctenocephalidae flea (18.4%) and two species of lice, L. vitulli (6.6%) and D. bovis (1.3%) were also recovered from dairy calves. In conclusion, the overall prevalence of calf internal and external parasites reported in the present study area was considerably high. This could affect the health and growth performance of dairy calves in the study ares. Therefore, as poorly managed calves are susceptible to most endo and ectoparasites, strategic deworming and acaricide application with subsequent implementation of improved calf management practices is warranted.Keywords: Dairy calf; External parasites; Internal parasites; Prevalence; Species composition

Analysis of Bm86 conserved epitopes: is a global vaccine against Cattle Tick Rhipicephalus microplus possible?

The cattle tick Rhipicephalus microplus causes significant economic losses in agribusiness. Control of this tick is achieved mainly through the application of chemical acaricides, often resulting in contamination of animal food products and of the environment. Another major concern associated with acaricide use is the increasing reports of resistance of this tick vector against the active ingredients of many commercial products. An alternative control method is vaccination. However, the commercially available vaccine based on a protein homologous to Bm86 exhibits variations in efficacy relative to the different geographical locations. This study aimed to identify antigenic determinants of the sequences of proteins homologous to Bm86. Phylogenetic analyses were performed to determine the extent of divergence between different populations of R. microplus to identify the sequence that could be used as a universal vaccine against the multiple geographically distinct populations of R. microplus and related tick species. Considering the extensive sequence and functional polymorphism observed among strains of R. microplus from different geographical regions, we can conclude that it may be possible to achieve effective vaccination against these cattle ticks using a single universal Bm86-based antigen.

Comparison of susceptibility of two Iranian populations of Tetranychus urticae Koch (Acari: Tetranychidae) to spirodiclofen

Two-spotted spider mite, Teranychus urticae (Acari: Tetranychide), is one of the most important agricultural pests throughout the world. The high reproductive potential, short life cycle, combined with frequent acaricide applications has resulted in resistance development to a wide range of acaricides. Resistance to acaricides has an important role in inefficiency of chemical control of this pest. In the present study, the susceptibility of two populations of two-spotted spider mite collected from Karaj (KrS) and Mahallat (MhR) to spirodiclofen was investigated. The bioassay was conducted using a leaf-dip method on same-age protonymphs. Bioassay results showed that there was a significant difference between LC 50 values of KrS and MhR populations. The resistance ratio was obtained as 22.19. The synergistic effects of triphenyl phosphate (TPP), piperonyl butoxide (PBO) and diethyl maleate (DEM) were assessed using residual contact vial (RCV) bioassay method. Results of the synergistic studies showed significant differences between LC 50 values of spirodiclofen with spirodiclofen + PBO and spirodiclofen + TPP in MhR population. The most synergistic effect in MhR population was related to PBO. The results of enzyme assays revealed that the most ratio activity in MhR population to KrS population was related to cytochrome P450 monoxygenase (3.02) and the lowest ratio activity was related to glutathione S-transferase (GST) (1.40). These results confirmed that esterase and cytochrome P450 monoxygenase are probably involved in resistance of T. urticae to spirodiclofen.

Sublethal effects of chlorfenapyr on the life table parameters of two-spotted spider mite, Tetranychus urticae (Acari: Tetranychidae)

The two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) is a well-known pest mite with an extensive host range worldwide. The control of T. urticae populations mostly relies on the application of synthetic acaricides or pesticides. Chlorfenapyr is a broad spectrum insecticide/miticide effective against agriculturally important pests. In this study, sublethal effects (LC10, LC20 and LC30) of this insecticide on demographic parameters of T. urticae based on the age-stage, two-sex life table theory were investigated under laboratory conditions [25 ± 2 °C, 60 ± 5 % RH and 16:8 (L:D) h]. According to the obtained results, the LC50 value for females of T. urticae was 47.66 ppm. The egg incubation, protonymph, as well as deutonymph durations of both sexes were significantly reduced as a consequence of treatment with LC20 and LC30 of chlorfenapyr. In addition, our results indicated that oviposition period in LC10 lasted 9.62 days, which was closer to the control (9.73 days); while it significantly decreased with increasing the concentration from LC20 to LC30. Furthermore, LC20 and LC30 treatments decreased the fecundity of females by 55.5% and 61.6%, respectively. The values of both intrinsic (r) and finite rates of increase (λ) at LC20 and LC30 was significantly inferior to other experimental treatments. It could be concluded that along with the lethal doses, the sublethal concentrations of chlorfenapyr profoundly reduced the population growth rate of T. urticae.

Endocrinologia e controle da vitelogênese em carrapatos

Background : : : : Ticks are distributed worldwide, with impacts on human and animal health. The cattle tick Rhipicephalus (Boophilus) microplus is the main parasite that affects livestock in tropical and subtropical regions of the world, causing large economical losses. Tick control methods are based on the application of chemical acaricides, which has resulted in selection of resistant ticks and a potential risk of environmental pollution and food contamination. Vaccines have showed to be a feasible tick control method that offers a cost-effective, environmental friendly alternative to chemical control. However, more than ten years after the commercialization of the first vaccine against ticks, the identification of tick-protective antigens remains a limiting step in the development of an efficient formulation that would avoid the use of chemical acaricides. So, the study of parasite biology and understanding physiological mechanisms could be a good strategy to find new targets for an efficient vaccine. Review : It was reviewed the main insights about the reproductive process in ticks, emphasizing the hormonal control of vitellogenesis and enzymes involved in vitellin processing during embryogenesis. The processes of vitellogenesis and embryogenesis have been studied in various organisms, particularly in cockroaches, flies and ticks. Although the roles of 20-hydroxyecdysone (20E) and juvenile hormone have been well characterized for vitellogenesis in insects, we know much less about the hormonal control of vitellogenesis in ticks. Initially, it was hypothesized that juvenile hormone was involved in tick vitellogenin-synthesis. However, more critical studies uncovered no evidence for the occurrence of juvenile hormone or juvenile hormone-like molecules in several tick species. Current research shows that in ticks, it appears that ecdysteroids, and not juvenile hormone, regulate the expression of the vitellogenin gene and the synthesis and release of vitellogenin protein into the hemolymph. In general, the carbohydrate, lipid and amino acid composition of tick vitellogenin is similar to that of insect vitellogenin. Once in the hemolymph, oocytes uptake vitellogenin through receptor-mediated endocytosys. However, there are different strategies to control vitellogenin synthesis and uptake by ovary in ixodide ticks. In the oocytes, vitellogenin is partially processed in the endosomal compartment and then stored as vitellin, the main reserve of protein for embryo development, in specialized organelles, the yolk granules. Embryo development depends on the availability of yolk material stored into oocytes. So, the characterization of molecules involved in vitellogenesis and embryo development contribute to a better understanding of the tick parasite physiology. During embryogesesis, acidic enzymes are responsible for the availability of this material and embryo nutrition. The Vitellin-Degrading Cysteine Endopeptidase (VTDCE), Boophilus Yolk Pro-Cathepsin (BYC) and Tick Heme Binding Aspartic Proteinase (THAP) are enzymes involved in vitellin hydrolysis in R. microplus eggs. These enzymes are produced by gut and fat body and transported through the hemolymph to be internalized into the oocytes and then play their role in tick embryo nutrition. As VTDCE, BYC and THAP are involved in an important physiological process, their potential as targets in an anti-tick vaccine is an attractive research topic. With this objective, various enzymes have been tested in native or recombinant forms as candidate immunogens to a multiantigenic anti-tick vaccine. Conclusion : Significant advancements have been made in recent years on understanding the tick reproductive process, and some molecules that can be possible targets for development of new tick control strategies have been characterized.

Toxicity of acaricides to and the behavioural response of Steneotarsonemus concavuscutum (Acari: Tarsonemidae)

Steneotarsonemus concavuscutum Lofego and Gondim Jr. causes chlorosis, necrosis, deformation, resinosis and death of coconut fruit (Cocos nucifera L.). These types of damage are commonly interpreted to result from Aceria guerreronis Keifer. The control of mites in coconut fruits is carried out primarily by acaricide applications. However, no records exist on the effectiveness of acaricides for S. concavuscutum control. Therefore, this study aimed to evaluate the toxicity of acaricides registered for the control of A. guerreronis on S. concavuscutum, in addition to analysing the walking behaviour of tarsonemid mites when exposed to the products. The behaviour of mites exposed to acaricides was studied with a video-tracking system in choice and no-choice arenas treated with acaricides. The LC50 estimate for abamectin and fenpyroximate was 1.1 mg/L and 2757 mg/L, respectively. Azadirachtin, spirodiclofen and hexythiazox caused mortality of up to 25%. Only exposure to abamectin reduced the number of mites that reached the perianth and remained live, but no difference was observed in the number of eggs found at this site. No acaricide showed an ovicidal or sterilizing effect on the females. The total distance walked and the walking velocity were higher when S. concavuscutum was exposed to azadirachtin and lower when exposed to abamectin. All acaricides irritated S. concavuscutum; however, repellence was observed in only 5% of the tested population for abamectin and azadirachtin. Among the products recommended for the control of A. guerreronis, only abamectin showed potential in controlling S. concavuscutum.

UV-C irradiation as a management tool for Tetranychus urticae on strawberries.

Tetranychus urticae Koch, the two-spotted spider mite, is a highly polyphagous and worldwide pest of many agricultural crops, including fruit, vegetables, and ornamentals. Typical methods of control include applications of acaricides and biological control agents. Here, we present a non-chemical technology for management of T. urticae on strawberry plants through the use of a nightly short-duration ultraviolet-C (UV-C) irradiation treatment. Potted strawberry plants infested with T. urticae that received a nightly 60-s exposure of UV-C irradiation had significantly fewer live mites per mid-canopy leaflet (fewer than five) than untreated control plants (> 175). Furthermore, none of the UV-C irradiated strawberry plants had any spider mite webbing; whereas, 65% of untreated plants were webbed. Tetranychus urticae feeding on untreated plants caused significant yellowing of the leaves compared with UV-C-treated plants. The UV-C irradiation treatment maintained mite populations below the accepted economic threshold of five mites per mid-canopy leaflet. No phytotoxic effects were visible on plants exposed to the short-duration nightly UV-C irradiation treatments. Further discussion is provided on the potential benefits of UV-C irradiation for mite management. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.

Evaluation of the protective efficacy of Ornithodoros moubata midgut membrane antigens selected using omics and in silico prediction algorithms

The African argasid tick Ornithodoros moubata transmits two important pathogens, the African swine fever virus and the spirochete Borrelia duttoni, the cause of human relapsing fever. To date, only conventional control measures such as widespread application of acaricides, strict control measures, and animal movement restrictions have been implemented to confine these diseases. Vaccines against tick infestations have the potential to be among the most efficacious interventions for the management of these diseases. Plasma membrane-associated proteins upregulated in tick midgut cells in response to blood feeding and digestion are thought to play vital functions in tick physiology and in the transmission of tick-borne pathogens. In addition, their antigenic extracellular regions are easily accessible to antibodies synthesised by immunised hosts, which makes them interesting targets for tick vaccine design. The mialomes (midgut transcriptomes and proteomes) of unfed O. moubata females and of engorged females at 48 h post-feeding have recently been obtained, providing a wealth of predicted midgut protein sequences. In the current study, these mialomes were screened using in silico tools to select predicted antigenic transmembrane proteins that were upregulated after feeding (516 proteins). The functionally annotatable proteins from this list (396 proteins) were then manually inspected following additional criteria in order to select a finite and easy-manageable number of candidate antigens for tick vaccine design. The extracellular antigenic regions of five of these candidates were obtained either as truncated recombinant proteins or as KLH-conjugated synthetic peptides, formulated in Freund’s adjuvant, and individually administered to rabbits to assess their immunogenicity and protective potential against infestations by O. moubata and the Iberian species Ornithodoros erraticus. All candidates were highly immunogenic, but provided low protection against the O. moubata infestations (ranging from 7% to 39%). Interestingly, all candidates except one also protected against infestations by O. erraticus, achieving higher efficacies against this species (from 20% to 66%). According to their protective potential, three of the five antigens tested (Om17, Om86 and OM99) were considered little suitable for use in tick vaccines, while the other two (OM85 and OM03) were considered useful antigens for tick vaccine development, deserving further studies.

Chemical tick control practices in southwestern and northwestern Uganda

Tick acaricide failure is one of the leading challenges to cattle production in Uganda. To gain an understanding into the possible drivers of acaricide failure, this study characterized the current chemical tick control practices in the southwestern (Mbarara, Mitooma and Rukungiri districts) and northwestern (Adjumani district) regions of Uganda. A total of 85 farms participated in a survey that utilized a semi-structured questionnaire. Moreover, ticks were collected to determine the most common species on the farms. Tick acaricide failure was mainly encountered in the districts where 95% (60/63) of the farms reared exotic cattle (dairy cross-breeds) under a paddocking (fenced) system. In the northwestern region, local cattle were reared in communal grazing areas. All farms used chemical acaricides for tick control, predominantly amidine (amitraz) (48%, 41/85) and co-formulated organophosphates and pyrethroids (38%, 32/85). The spraying method was the most common (91%, 77/85) acaricide application technique, with cattle crush (81%, 69/85) as a common means of physical restraint. Less than optimal tick control practices encountered included use of substandard equipment for spraying, inappropriate dilutions, frequent interaction between animals in neighboring farms despite lack of synchronized chemical tick control and malpractices in acaricide rotation. Only Rhipicephalus appendiculatus and R. (Boophilus) decoloratus ticks were found in the southwestern region, where 51% (32/63) of the farmers used high acaricide concentrations above the manufacturers’ recommendation. Farmers in the northwestern region used 2.2 times less acaricide volume per cattle than those in the southwestern region, and more diverse tick species were encountered. Toxic effects of acaricide to cattle and workers were reported by 13% (11/85) and 32% (27/85) of the respondents, respectively. All 27 cases of human acaricide toxicity reported were from the southwestern region. Overall, our findings may inform strategies for more prudent chemical tick control and safe acaricide handling to benefit animal welfare, food safety and public health.

Efficacy Evaluation of Six Entomopathogenic Nematode Speciesagainst Engorged Females of Southern Cattle Fever Tick,Rhipicephalus(=Boophilus)microplus

The southern cattle fever tick, Rhipicephalus microplus Canestrini, is widely distributed in tropical and subtropical regions, causing huge economic losses to milk and meat production. Application of acaricides is the most widely used control strategy, but because of increasing evidence of resistance to acaricide and environmental concerns, novel strategies are needed. Use of entomopathogenic nematodes is a promising alternative for tick control. Six species of nematodes, Steinernema riobrave Cabanillas, Poinar, and Raulston (355 strain), S. carpocapsae (Weiser) (All strain), S. feltiae Filipjev (SN strain), Heterorhabditis bacteriophora Poinar (VS strain), H. indica Poinar, Karunakar, and David (HOM1 strain), and H. floridensis Nguyen, Gozel, Koppenhofer, and Adams (K22 strain) were tested for pathogenicity against R. microplus (Deutch strain). Engorged female ticks were exposed to 1,250, 2,500, and 5,000 infective juvenile nematodes for 24, 48, and 72 hours in Petri dishes, and tick mortality over time, pre-oviposition period, egg mass weight, reproductive index, percentage inhibition of oviposition, and hatching percentage were evaluated. Dose-dependent mortality was recorded in Heterorhabditis species S. riobrave and S. carpocapsae which increased with exposure time. Minimum LC50 (95% CL) values of 1999 (1947–2052) and 69 (63–75) infective juveniles per Petri dish were calculated for S. riobrave and H. floridensis, respectively, at 72 hours of exposure. Infective juvenile concentration and exposure time did not influence the pre-oviposition period. Differences in egg mass weight and reproductive index among the treatments and check group were observed with respect to concentration and exposure time. Reduction in hatchability was recorded only in ticks exposed to S. riobrave. Overall, H. floridensis was the most virulent species against engorged R. microplus females, adversely impacting most biological parameters. S. riobrave showed potential especially because it is native to South Texas and commercially produced. Future studies are warranted to evaluate the potential of this nematode species for biological control of the cattle fever tick under field conditions.

Acaricide-Mediated Competition Between the Sibling Species Tetranychus cinnabarinus and Tetranychus urticae.

The carmine spider mite (Tetranychus cinnabarinus [Acarifonnes: Tetranychidae]) and the two-spotted spider mite (Tetranychus urticae [Acarifonnes: Tetranychidae]) are two notorious pests of agricultural crops. Control of these pests has been dependent upon using different kinds of acaricides. The purpose of this study was to determine the differential responses of these two pest species collected from crops in the same field to acaricide treatments. Field trials have shown that without spraying acaricides, T. cinnabarinus will displace T. urticae. However, the application of abamectin has the potential to change the composition of spider mite complexes and facilitate the interspecific competition of T. urticae against T. cinnabarinus when both are fed on cowpeas and eggplants. Moreover, T. urticae is more prone to develop resistance than T. cinnabarinus when selected in the laboratory using cyflumetofen or fenpropathrin. After 20 generations of acaricide selection, the activities of detoxifying enzymes were considerably higher in T. urticae with more detoxifying enzymes upregulated after selection in this species. The results of this study demonstrate that differential responses to acaricide treatments have made it possible for T. urticae to overcome the competitive advantage present in T. cinnabarinus during the absence of acaricide application.

First report of the effect of Ocotea elegans essential oil on Rhipicephalus (Boophilus) microplus

Rhipicephalus (Boophilus) microplus is responsible for reducing animal welfare, causing a drop in productive performance and transmitting hemoparasites. The main strategy of tick control is application of synthetic acaricides. However, parasite resistance to these compounds is a major concern. Therefore, the acaricidal and repellent in vitro effect of the Ocotea elegans essential oil on larvae and adult females of R. (B.) microplus were evaluated. The larval packet test (LPT), larval repellency test (RT) and adult immersion test (AIT) were performed. The essential oil was analyzed by gas chromatography (GC/FID) and the structure of the oil’s major constituent (92.2% sesquirosefuran) was elucidated by nuclear magnetic resonance. In the AIT, efficacy higher than 90% was detected from the concentration 25 mg/mL upward. In both LPTs performed after 48 h, only the 100 mg/mL concentration resulted in mortalities above 70%. On the other hand, the essential oil caused an average of 95.8% repellency from 0.78 to 100 mg/mL. The LC50 in the two LPT (48 h) tests were 59.68 and 25.59 mg/mL, respectively. The LC50 and LC90 in the AIT were 4.96 and 17.37 mg/mL, and in the RT they were 0.04 and 1.24 mg/mL respectively. We conclude that the essential oil of O. elegans leaves has a significant acaricidal effect on engorged females and on larval repellency of R. (B.) microplus ticks, and can be a promising alternative for the control of this ectoparasite.

Liposome mediated double-stranded RNA delivery to silence ribosomal protein P0 in the tick Rhipicephalus haemaphysaloides

Control of ticks has been achieved primarily by the application of acaricides, which has drawbacks such as environmental contamination leading to the selection of pesticide-resistant ticks. The potential of dsRNA to suppress genes critical for tick survival due to its sequence specificity suggests that dsRNAs could be developed as tailor-made pesticides. In this study, the dsRNA of P0 gene from the tick, Rhipicephalus haemaphysaloides, was evaluated as a potential anti-tick agent. Effects of using different dsRNA delivery methods were tested by quantitative RT-PCR and tick bioassays to determine survival, feeding and reproduction. The results showed that P0 dsRNAs could be effectively delivered into ticks and silenced by incubating with liposomes. Incubation time was found to be the most important factor in dsRNA delivery and gene silencing compared with liposome types and dsRNA concentration. The effects of P0 dsRNA treatment on ticks were found to be significant on blood feeding, molting or reproduction. These data show that anti-tick agents based on dsRNAs could have potential use in tick control.

The effects of acaricide treatment of sheep on red grouse Lagopus lagopus scotica tick burdens and productivity in a multi-host system.

Ixodes ricinus (Ixodida: Ixodidae) ticks are of economic and pathogenic importance across Europe. Within the uplands of the U.K., management to reduce ticks is undertaken to benefit red grouse Lagopus lagopus scotica (Galliformes: Phasianidae). Management strategies focus on the acaricide treatment of domestic sheep Ovis aries (Artiodactyla: Bovidae), but the effectiveness of this is less certain in the presence of wild hosts, particularly red deer Cervus elaphus (Artiodactyla: Cervidae) and mountain hare Lepus timidus (Lagomorpha: Leporidae). This study examines the effects of sheep management on grouse tick burdens and productivity using sites with a range of wild host densities. Sites at which applications of acaricide were more frequent had lower tick burdens; this relationship was similar on sites with a range of deer densities. However, no direct link was detected between acaricide treatment interval and grouse productivity. Sites with higher deer densities had higher grouse tick burdens and lower productivity [mean ± standard error (SE) young:adult ratio: 1.2 ± 0.2] compared with sites with lower deer densities (mean ± SE young:adult ratio: 1.8 ± 0.1). Sites with higher grouse brood sizes and higher proportions of hens with broods were also those with higher mountain hare abundance indices. This study highlights the importance of the frequent treatment of sheep with acaricide to reduce tick burdens on grouse, even in the presence of wild hosts.

Ambulatory dispersal of the susceptible and propargite-resistant strains of Tetranychus urticae and its influence on pesticide resistance dynamics

The distribution of resistant individuals is determined by the amount of movement between populations. The differential rate of dispersal of a susceptible and a pesticide-resistant strain could influence the resistance dynamics under field conditions. The dispersal rate and dispersal efficiency of the susceptible and propargite-resistant strains of Tetranychus urticae were measured in separate-release and mixed-release experiments. The diffusion coefficient (D) of both strains did not differ significantly (P>0.344) and an estimate of the asymptotic rate of advance (2√rD) (for one generation) was estimated at 0.1047 and 0.0930cm per degree day for the susceptible and propargite-resistant strains, respectively. The dispersal efficiency of the two strains differed significantly (P<0.005) as more susceptible mites than propargite-resistant mites crossed into specified zones more quickly after 290 and 366 degree days. Significantly (P<0.05) higher number of susceptible adults, immatures and eggs were found in the outer most zone of an arena as compared to that of the propargite-resistant mites. The bioassay of the two strains showed a similar pattern of the spread of the adult females across the specified zones in the mixed-release experiment. The relatively lower dispersive tendency of the propargite-resistant T. urticae and the smaller proportion of adult females exhibiting that behaviour increase the chances of developing resistant ‘hotspots’ in field specially after an acaricide application.

Immunofluorescent detection in the ovary of host antibodies against a secretory ferritin injected into female Haemaphysalis longicornis ticks

Due to the continuous threat of ticks and tick-borne diseases to human and animal health worldwide, and the drawbacks of chemical acaricide application, many researchers are exploring vaccination as an alternative tick control method. Earlier studies have shown that host antibodies can circulate in the ticks, but it has not been confirmed whether these antibodies can be passed on to the eggs. We previously reported that ticks infesting rabbits immunized with a recombinant secretory ferritin of Haemaphysalis longicornis (HlFER2) had reduced egg production and hatching. Here we attempted to detect the presence of antibodies against HlFER2 in the ovary and eggs of female ticks through immunofluorescent visualization. Purified anti-HlFER2 antibodies or rabbit IgG for control was directly injected to engorged female H. longicornis. Ovaries and eggs after oviposition were collected and prepared for an indirect immunofluorescent antibody test. Positive fluorescence was detected in ovaries one day post-injection of anti-HlFER2 antibodies. Through silencing of Hlfer2 gene, we also determined whether the injected antibodies can specifically bind to native HlFER2. Immunofluorescence was observed in the oocytes of dsLuciferase control ticks injected with anti-HlFER2 antibodies, but not in the oocytes of Hlfer2-silenced ticks also injected with anti-HlFER2 antibodies. Our current findings suggest that host antibodies can be passed on to the oocytes, which is significant in formulating a vaccine that can disrupt tick reproduction.