Antimicrobial activity in the egg wax of the tick Amblyomma hebraeum (Acari: Ixodidae) is associated with free fatty acids C16:1 and C18:2

Toxicity of Common Acaricides, Disinfectants, and Natural Compounds against Eggs of Rhipicephalus annulatus

Ticks pose a significant threat due to their ability to lay thousands of eggs, which can persist in the environment for extended periods. While the impact of various compounds on adult and larval ticks has been studied, research on their efficacy against tick eggs is limited. This study evaluated the ovicidal activity of commercial acaricides, disinfectants, and natural products against Rhipicephalus annulatus eggs using the egg hatch assay (EHA). Deltamethrin and cypermethrin caused a non-significant inhibition of hatching (IH%), even at concentrations higher than the recommended levels. By contrast, the acaricides chlorpyrifos, phoxim, and amitraz significantly inhibited hatching at all tested concentrations. Ivermectin also demonstrated significant IH% at various concentrations but did not fully inhibit the hatching process. Among the disinfectants tested, Virkon-S®, TH4, and Chlorox showed insignificant effects, whereas formalin achieved an IH% of only 34.1% at a high concentration of 200 mg/mL. Natural products, carvacrol and thymol, exhibited significant ovicidal activity, with a significant IH%. In a semi-field application, phoxim (0.5 mg/mL) and deltamethrin (0.05 mg/mL) were sprayed on tick eggs on pasture soil from a farm. The results indicated that phoxim-treated eggs had a 40% IH%, while deltamethrin-treated eggs showed only an 8.79% IH%. In conclusion, the acaricides amitraz, phoxim, and chlorpyrifos, as well as the natural products carvacrol and thymol, caused significant toxicity to R. annulatus eggs.

Evaluation of the biological function of ribosomal protein S18 from cattle tick Rhipicephalus microplus

Rhipicephalus (Boophilus) microplus, also known as the cattle tick, causes severe parasitism and transmits different pathogens to vertebrate hosts, leading to massive economic losses. In the present study, we performed a functional characterization of a ribosomal protein from R. microplus to investigate its importance in blood feeding, egg production and viability. Ribosomal protein S18 (RPS18) is part of the 40S subunit, associated with 18S rRNA, and has been previously pointed to have a secondary role in different organisms. Rhipicephalus microplus RPS18 (RmRPS18) gene expression levels were modulated in female salivary glands during blood feeding. Moreover, mRNA levels in this tissue were 10 times higher than those in the midgut of fully engorged female ticks. Additionally, recombinant RmRPS18 was recognized by IgG antibodies from sera of cattle naturally or experimentally infested with ticks. RNAi-mediated knockdown of the RmRPS18 gene was performed in fully engorged females, leading to a significant (29 %) decrease in egg production. Additionally, egg hatching was completely impaired, suggesting that no viable eggs were produced by the RmRPS18-silenced group. Furthermore, antimicrobial assays revealed inhibitory activities against gram-negative Escherichia coli and gram-positive Staphylococcus aureus bacteria, affecting bacterial growth. Data presented here show the important role of RmRPS18 in tick physiology and suggest that RmRPS18 can be a potential target for the development of novel strategies for tick control.

Fine structural characteristics of the chorionic microspheres on the egg surface of the orb web spider Trichonephila clavata

The eggs laid by the orb web spider Trichonephila clavata must overwinter in bitterly freezing and dry conditions before hatching, but there does not seem to be any protection like a compact silk case covering the entire eggmass. Instead, the surface of the eggmass is completely coated with a milky coating called chorionic microspheres (CM). Therefore, we investigated the fine structural characteristics of CM to demonstrate their ecological importance. Although the diameter of CM in outer eggmass exhibits a significant variation, the chorionic surface is coated with a single layer of CM, characterized by a consistent diameter of approximately 2.3 µm. The surface structure of aggregated CM shows short papillary projections demonstrating segmental adhesion of mucous components. CM is insoluble in water but partially soluble in anhydrous ethanol, and its spherical structure is completely decomposed by hexafluoroisopropanol (HFIP), a strong organic solvent. Since our fine structural observations clearly show that CM is not derived from vitellogenic or choriogenetic processes, the CM adhesive coatings during ovipositional process appears to be equivalent to cocoon silk for various protective functions in silken eggcase.

Predation of ant species Lasius alienus on tick eggs: impacts of egg wax coating and tick species

Several animal species, including ants, have been reported to be capable of predation on ticks. However, determining factors in most interactions between ticks and predators have not yet been fully deciphered. We hypothesized that the ant species Lasius alienus, which is unknown whether it has any impact on ticks, may exhibit predation on the eggs of tick species Hyalomma marginatum, H. excavatum, and Rhipicephalus bursa, and that the tick egg wax can be the main determinant in possible predation. In the study, 6300 tick eggs with the natural wax coating (waxed/untreated) and 2700 dewaxed tick eggs, the wax of which was removed in the laboratory, were repeatedly presented to the foraging workers belonging to three different ant nests in their natural habitat. Depending on the tick species and trials, the rate of the eggs carried by the ants ranged from 12.8 to 52.1% in the waxed and from 59.8 to 78.4% in the dewaxed eggs. It was observed that the dewaxing process both increased the interest of the ants in the eggs and resulted in a reduction in the variation associated with tick species. This study showed that L. alienus has a predatory effect on tick eggs, the severity of this impact is closely associated with the tick species, the tick-associated difference is caused by the species-specific property of the egg wax, and the variety in the protective effects of the wax seems to be an evolutional result of the biological and ecological adaptation process of the species.

Interfering with cholesterol metabolism impairs tick embryo development and turns eggs susceptible to bacterial colonization

Cholesterol is a known precursor of arthropod molecules such as the hormone 20-hydroxyecdysone and the antimicrobial boophiline, a component of tick egg wax coat. Because the cholesterol biosynthetic pathway is absent in ticks, it is necessarily obtained from the blood meal, in a still poorly understood process. In contrast, dietary cholesterol absorption is better studied in insects, and many proteins are involved in its metabolism, including Niemann-Pick C (NPC) transporter and acyl-CoA:cholesterol acyltransferase (ACAT), as well as enzymes to convert between free cholesterol and esterified cholesterol. The present work addresses the hypothesis that tick viability can be impaired by interfering with cholesterol metabolism, proposing this route as a target for novel tick control methods. Two drugs, ezetimibe (NPC inhibitor) and avasimibe (ACAT inhibitor) were added to calf blood and used to artificially feed Rhipicephalus microplus females. Results show that, after ingesting avasimibe, tick reproductive ability and egg development are impaired. Also, eggs laid by females fed with avasimibe did not hatch and were susceptible to Pseudomonas aeruginosa adhesion and biofilm formation in their surfaces. The immunoprotective potential of ACAT against ticks was also accessed using two selected ACAT peptides. Antibodies against these peptides were used to artificially feed female ticks, but no deleterious effects were observed. Taken together, data presented here support the hypothesis that enzymes and other proteins involved in cholesterol metabolism are suitable as targets for tick control methods.

Dominant egg surface bacteria of Holotrichia oblita (Coleoptera: Scarabaeidae) inhibit the multiplication of Bacillus thuringiensis and Beauveria bassiana

Holotrichia oblita (Coleoptera: Scarabaeidae) and some other scarab beetles are the main soil-dwelling pests in China. Bacillus thuringiensis (Bt) and Beauveria bassiana (Bb) are entomopathogens that have been used as biocontrol agents of various pests. However, scarab larvae especially H. oblita exhibited strong adaptability to these pathogens. Compared to other scarabs, H. oblita could form a specific soil egg case (SEC) structure surrounding its eggs, and young larvae complete the initial development process inside this structure. In this study, we investigated the role of SEC structure and microorganisms from SEC and egg surface in pathogen adaptability. 16S rRNA gene analysis revealed low bacterial richness and high community unevenness in egg surface, with Proteobacteria, Firmicutes, Bacteroidetes and Fusobacteria dominating. In terms of OTUs composition analysis, the data show that the egg surface contains a large number of unique bacteria, indicating that the egg bacterial community may be derived from maternal transmission. Furthermore, we found that all culturable bacteria isolated from egg surface possessed antimicrobial activity against both Bt and Bb. The Pseudomonas bacteria with a significantly higher abundance in egg surface showed strong Bt- and Bb antagonistic ability. In conclusion, this study demonstrated a unique and antimicrobial bacterial community of H. oblita egg surface, which may contribute to its adaptability. Furthermore, the specific SEC structure surrounding the H. oblita eggs will provide a stable microenvironment for the eggs and egg surface bacteria, which probably provides more advantages for H. oblita adaptation ability.

Botanical acaricides induced morphophysiological changes of reproductive and salivary glands in tick: A mini-review

Ticks are obligate hematophagous ectoparasites and important vectors of several pathogens of medical and veterinary significance, in addition to economic losses associated with their infestation. The primary method for the current control of tick is the use of synthetic acaricides, and many studies have focused on the tick control efficacy associated with the use of synthetic acaricides. However, the intensive use of these compounds has environmental and public health implications, in addition to the development of resistant tick populations. Over the years, studies have demonstrated the great potential of botanicals as an effective alternative in tick control. Most of the reviews on the acaricidal activity of botanicals focused on the effects relating to the development, reproduction, and mortality rate of ticks. Besides this acaricidal activity, botanicals can also affect the morphophysiology of the reproductive organs and the salivary glands that are important for tick procreation and survival. Effects relating to histopathological and cell ultra-structural alterations caused by botanical acaricides can be determined through microscopy techniques. Hence, the present mini-review focuses on studies dealing with morphophysiology changes of the reproductive system and the salivary gland of ticks exposed to botanical acaricides, with a view of expanding our knowledge for the future integrative application of botanical acaricides in tick control.

Eggshell spheres protect brown widow spider ( Latrodectus geometricus) eggs from bacterial infection

Eggs provide a rich source of nutrients for the developing embryo, making them a favoured food source for other organisms as well. Several defence mechanisms have evolved to protect the developing embryos against microbial threats. In this article, we elucidate the defence strategy of brown widow spider ( Latrodectus geometricus) eggs against bacteria. Antibacterial activity was shown by inhibition of bacterial growth on agar plate, liquid culture and retarded biofilm formation. The defence strategy against bacterial invasion was demonstrated in the whole egg, whole egg extract, egg surface extract, eggshell and eggshell extract. The source and characteristics of this antibacterial activity are distinctive and stem in part from a dense layer of spheres covering the egg surface, likely originated from the oviposition fluid. The spheres are rich in low-molecular-weight proteins, yet their exact composition remains unknown. In this study, we demonstrate that the egg surface is hydrophobic, while the spheres are superhydrophilic. Egg surface roughness and hydrophobicity combined with its antibacterial chemical properties reduce the ability of bacteria to grow on the egg surface. Understanding the properties of these unique structures may contribute significantly to our knowledge of how nature deals with bacterial infections.

Sterile Capsule-Egg Cocoon Covering Constitutes an Antibacterial Barrier for Spider Parasteatoda tepidariorum Embryos

Coexistence of organisms and pathogens has resulted in the evolution of efficient antimicrobial defense, especially at the embryonic stage. This investigation aimed to substantiate the hypothesis that the layers of silk in a spider cocoon play a role in the immunity of the embryos against microorganisms present in the external environment. A two-step interdisciplinary attempt has been made. First, the eggs and empty cocoons of the spider Parasteatoda tepidariorum were incubated on lysogeny broth agar media for 3 d. In the samples of eggs, no growth of bacteria was detected. This indicated that the eggs inside cocoons were sterile. Therefore, in the second step, the cocoons and egg surface were analyzed using SEM, TEM, and LM. The obtained images demonstrated that both inner and outer layers of the silk are built of threads of the same diameter, set in an irregular manner, and randomly clustered into groups. The threads in the outer layer were packed more densely than in the inner one. TEM analysis revealed threads of two types of fibrils and their arrangement. The resultant thread tangle of the cocoon, possibly correlated with the ultrastructure of the fibers, seems to be an example of a structure-function relationship playing a crucial ecoimmunological role in spider embryonic development.

Energy sources from the eggs of the wolf spider Schizocosa malitiosa: isolation and characterization of lipovitellins

In oviparous species, proteins and lipids found in the vitellus form the lipoproteins called lipovitellins that are the major source of energy for the development, growth, and survival of the embryo. The energy resources provided by the lipovitellins have not yet been investigated in the Order Araneae. Using the wolf spider Schizocosa malitiosa (Lycosidae) as an experimental model, we identified and characterized the lipovitellins present in the cytosol, focusing on the energetic contribution of those lipoprotein particles in the vitellus. Two lipovitellins (LV) named SmLV1 and SmLV2 were isolated. SmLV1 is a high-density lipoprotein with 67% lipid and 3.6% carbohydrate, and SmLV2 is a very high-density lipoprotein with 9% lipid and 8.8% carbohydrate. Through electrophoresis in native conditions we observed that SmLV1 has a molecular mass of 559 kDa composed of three apolipoproteins of 116, 87, and 42 kDa, respectively. SmLV2 comprised several proteins composed of different proportions of the same subunits (135, 126, 109, and 70 kDa). The principal lipids of these lipovitellins are sphingomyelin + lysophosphatidylcholine, esterified sterols, and phosphatidylcholine. Lipovitellin-free cytosol contains abundant phospatidylcholine and triacylglyceride related to the yolk nuclei (the vitellus organizing center). The principal fatty acids of SmLV1 and SmLV2 are 18:2 n-6, 18:1 n-9, and 16:0. Spectrophotometry detected no pigments in either the lipovitellins or the cytosol. The egg caloric content was 92 cal/g, at proportions of 59.8% protein, 20.1% carbohydrate, and 19.9% lipid. SmLV1 and SmLV2 provided 19.5% and 17.1% of the calories, respectively. Both lipovitellins contribute mainly with proteins (15.8-18%), with the input of carbohydrates and lipids being lower than 1.3%.

Egg wax from the cattle tick Rhipicephalus (Boophilus) microplus inhibits Pseudomonas aeruginosa biofilm

Rhipicephalus (Boophilus) microplus is constantly challenged during its life cycle by microorganisms present in their hosts or in the environment. Tick eggs may be especially vulnerable to environmental conditions because they are exposed to a rich and diverse microflora in the soil. Despite being oviposited in such hostile sites, tick eggs remain viable, suggesting that the egg surface has defense mechanisms against opportunistic and/or pathogenic organisms. R. microplus engorged females deposit a superficial wax layer onto their eggs during oviposition. This egg wax is essential for preventing desiccation as well as acting as a barrier against attack by microorganisms. In this study, we report the detection of anti-biofilm activity of R. microplus egg wax against Pseudomonas aeruginosa PA14. Genes involved in the functions of production and maintenance of the biofilm extracellular matrix, pelA and cdrA, respectively, were markedly downregulated by a tick egg-wax extract. Moreover, this extract strongly inhibited fliC gene expression. Instead of a compact extracellular matrix, P. aeruginosa PA14 treated with egg-wax extract produces a fragile one. Also, the colony morphology of cells treated with egg-wax extract appears much paler and brownish, instead of the bright purple characteristic of normal colonies. Swarming motility was also inhibited by treatment with the egg-wax extract. The inhibition of P. aeruginosa biofilm does not seem to depend on inhibition of the quorum sensing system since mRNA levels of the 3 regulators of this system were not inhibited by egg-wax extract.

A steroidal molecule present in the egg wax of the tick Rhipicephalus (Boophilus) microplus inhibits bacterial biofilms

The cattle tick Rhipicephalus (Boophilus) microplus lays eggs in the soil near the roots of grass, or in similar highly moist environments that are prone to biofilm formation. Tick eggs have a protective wax coating that may be a source of nutrients for microorganisms. However, as the eggs remain viable and show no visible signs of microbial colonization, we hypothesized that the coating might have anti-biofilm properties. We show here that the coating inhibits biofilm formation by both Gram-negative and Gram-positive bacteria, though by different mechanisms. We have identified the anti-biofilm molecule as N-(3-sulfooxy-25-cholest-5-en-26-oyl)-L-isoleucine (boophiline), and we show that it inhibits the expression of fliC (flagellin) and cdrA (biofilm scaffold), whose products are necessary for biofilm formation in Pseudomonas aeruginosa. Boophiline is a novel biofilm inhibitor being also effective against Staphylococcus epidermidis biofilm. In our study we show evidences of the boophiline mode of action in the protection of arthropod eggs against biofilm colonization.