Inhibitory action of neem aqueous extract (azadirachta indica A. Juss) on the vitellogenesis of rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae) ticks

Histopathological effects of the fruit extract of Citrullus colocynthis on the ovary of the tick Hyalomma dromedarii

Hyalomma dromedarii is the predominant tick species parasitizing camels in Egypt which leads to mortalities in young animals that result in economic losses. It can transmit a lot of pathogens to animals and humans, such as the Crimean-Congo hemorrhagic fever virus, the Dhori virus, Kadam virus, Theileria annulata and spotted fever rickettsia. The continuous use of chemical acaricides has negative impact on the environment and almost led to acaricidal resistance, and hence the plant extracts represent alternative methods for controlling ticks. The present study was carried out to assess the histopathological effects on the ovary of fed female Hyalomma dromedarii following immersion in the ethanolic extract of fruits of Citrullus colocynthis (100 mg/mL). Light, scanning and transmission electron microscopy observations provided evidence that Citrullus colocynthis caused extensive damage to oocytes. Destruction of the internal organelles of oocytes, along with delay and/or inhibition of vitellogenesis were demonstrated. This is the first histological study that points to damage in H. dromedarii ovaries following treatment with the ethanolic extract of fruits of C. colocynthis. The data presented suggest that the plant extract affects the ovary either directly by entering the oocytes and/or indirectly by damaging the gut cells and digestion of blood that interfere with the development of oocytes, so it can be used as a promising agent for tick control.

Modulation of the PGE2-Mediated Pathway in the Eclosion Blocking Effect of Flumethrin and Terpenoid Subfraction Isolated from Artemesia nilagirica in Rhipicephalus annulatus

Prostaglandins are a group of important cell-signaling molecules involved in the regulation of ovarian maturation, oocyte development, egg laying and associated behaviors in invertebrates. However, the presence of prostaglandin E₂ (PGE₂), the key enzymes for PGE₂ biosynthesis and its interference by drugs were not investigated previously in the ovary of ticks. The present study was undertaken to assess the modulation of the PGE₂-mediated pathway in the eclosion blocking effect of flumethrin and terpenoid subfraction isolated from Artemisia nilagirica in Rhipicephalus annulatus ticks. The acaricidal activities and chemical profiling of the terpenoid subfraction were performed. The localization of the cyclooxygenase1 (COX1) and prostaglandin E synthase (PGES) enzymes and the quantification of PGE₂ in the ovaries of the ticks treated with methanol (control), flumethrin and terpenoid subfraction were also undertaken. In addition, the vitellogenin concentration in hemolymph was also assayed. Both flumethrin and the terpenoid subfraction of A. nilagirica elicited a concentration-dependent inhibition of fecundity and blocking of hatching of the eggs. The COX1 could not be detected in the ovaries of treated and control ticks, while there was no significant difference observed in the concentration of vitellogenin (Vg) in them. The presence of PGES in the oocytes of control ticks was confirmed while the immunoreactivities against PGES were absent in the vitellogenic oocytes of ticks treated with flumethrin and terpenoid subfraction. The levels of PGE₂ were below the detection limit in the ovaries of the flumethrin-treated ticks, while it was significantly lower in the ovaries of the terpenoid subfraction-treated ticks. Hence, the prostaglandin E synthase and PGE₂ were identified as very important mediators for the signaling pathway for ovarian maturation and oviposition in ticks. In addition, the key enzyme for prostaglandin biosynthesis, PGES and the receptors for PGE₂ can be exploited as potential drug targets for tick control. The detection of PGES by immunohistochemistry and quantification of PGE₂ by LC-MSMS can be employed as valuable tools for screening newer compounds for their eclosion blocking acaricidal effects.

Cytotoxic effects of Satureja montana L. essential oil on oocytes of engorged Rhipicephalus microplus female ticks (Acari: Ixodidae)

In addition to pesticidal activity, the capacity of natural compounds to inhibit the reproduction of parasites emerge as an important alternative tick control method. In this context, Satureja spp. stand out due to their recognized pesticidal properties. Among parasites of veterinary importance, the cattle tick, Rhipicephalus microplus, is responsible for great economic losses in livestock and transmission of relevant pathogens. Thus, the aim of this study was to evaluate the effects of different concentrations of the essential oil of Satureja montana L. on the ovary morphology of R. microplus engorged females through histological and histochemical techniques. The most remarkable morphological changes found were: cytoplasmic vacuolation of germ cells, irregular and thicker chorion, irregular oocyte shape, ring-shaped nucleolus, decrease in protein and carbohydrate content in oocytes, in addition to cellular changes in the oviduct and pedicel. All morphological changes were assessed using a semiquantitative method already established in the literature. Ticks exposed to 5.0 μl/ml of essential oil showed the most significant changes when compared to control groups. Thus, the essential oil of S. montana L. damaged the reproductive system of R. microplus, which may impair ticks' offspring production and promote a long-term control of this species. HIGHLIGHTS: The essential oil of Satureja montana L. affects the ovary morphology of the cattle tick. The main morphological alterations found were cytoplasmic vacuolation, irregular and thicker chorion and irregular oocyte shape. These alterations may impair the development of eggs.

In vivo and in vitro apoptosis induced by new acaricidal ethyl-carbamates in Rhipicephalus microplus

The ability of ethyl-4-bromophenylcarbamate (LQM 919) and ethyl-4-chlorophenylcarbamate (LQM 996) to induce in vivo apoptosis of Rhipicephalus microplus ovarian cells and in vitro apoptosis of tick and mammalian cell culture was evaluated. The ovaries of engorged females treated with 1 mg mL^-1 LQM 919 or LQM 996 presented more (p < 0.001) peroxidase-TUNEL-positive labeled cells (apoptotic cells) in situ than their respective control groups, and this increase was time-dependent (p < 0.001). The majority of apoptotic cells were observed in the epithelium and ovarian pedicel. HepG2, Vero and Rm-sus cells, as well as cells from primary cultures of R. microplus salivary glands, intestine and ovaries were exposed to different concentrations of the ethyl-carbamates. Both ethyl-carbamates induced a concentration-dependent reduction in the viability of all cell types (p < 0.001). Exposure to the ethyl-carbamates increased caspase 3 activity (p < 0.01) in primary cultures and cell lines, except in HepG2 cells. Fluorescent TUNEL-positive cells were observed in all cell types treated with 600 μM LQM 919 or LQM 996. These results indicate that both ethyl-carbamates induce apoptosis of the ovarian, intestinal and salivary glands cells in R. microplus and strongly suggest that this is their main mechanism of acaricidal action.

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.

Ultrastructural changes induced by the entomopathogenic fungus Beauveria bassiana in the ovary of the tick Argas (Persicargas) persicus (Oken)

The present study was carried out to assess the effects on the ovary of fed female Argas persicus following spraying of the ticks with spores of the fungus Beauveria bassiana suspended in triton X100 at a concentration of 10⁷ conidia/mL. Scanning and transmission electron microscopy observations provided evidence that B. bassiana invaded the ovary, causing extensive morphological damage and deterioration of the developing oocytes. Destruction of the shape and internal organelles of young and previtellogenic oocytes and complete inhibition of vitellogenesis was evident. This histopathological study is the first demonstration of ultrastructural damage in the ovaries of A. persicus after infection with B. bassiana. The data presented confirm that B. bassiana affects the ovary either directly by entering the oocytes and/or indirectly by producing toxins in the haemolymph that interfere with the development of oocytes, thus potentially contributing to the control of this tick in a way that is safe for its host and the environment.

Toxicity, repellency and anti-cholinesterase activities of thymol-eucalyptus combinations against phenotypically resistant Rhipicephalus annulatus ticks

The current study was designed to compare the acaricidal activity of pure thymol (T) crystals, eucalyptus oil (E), and their combinations (T + E) at concentrations ranging from 0.625 to 10% against phenotypically deltamethrin-resistant Rhipicephalus annulatus ticks. The adulticidal, larvicidal, ovicidal, and repellent activities of the tested compounds and their possible mechanism of action were studied. Thymol showed 93.3% adulticidal activity at 10% concentration, whereas at 2.5% it achieved 100% larvicidal activity. Eucalyptus oil had a significant effect on tick adults at concentrations > 5%, and at 10% concentration it showed 96.7% adulticidal activity and stopped the egg hatching. On deltamethrin-resistant larvae, the median lethal concentration (LD₅₀) was 0.61, 7.5, and 0.61% for T, E, and T + E combinations, respectively, and repellent activities were 85.7, 62.5, and 100% at the 10% concentration used. Combinations of T + E did not induce additional effects as adulticidal and larvicidal in a comparison with T treatments. The tick's acetylcholinesterase significantly decreased as a result of all treatments including deltamethrin, whereas lipid peroxidation significantly increased compared with the control untreated ticks. The glutathione content significantly decreased as a result of all treatments except for treatments with 10% thymol and its combination with eucalyptus oil. Moreover, 10% eucalyptus oil significantly decreased the tick's glutathione peroxidase and catalase activities reflecting the attenuation of antioxidant defense in the ticks. In conclusion, thymol and eucalyptus oil showed excellent activities against deltamethrin-resistant R. annulatus isolates. Their action may be mediated via acetylcholinesterase inhibition. The effect of thymol-eucalyptus combinations recorded higher activities as an ovicidal and as a repellent.

Thymol action on cells and tissues of the synganglia and salivary glands of Rhipicephalus sanguineus sensu lato females (Acari: Ixodidae)

Thymol is a monoterpene present in plants of the families Lamiaceae, Verbenaceae and Apiaceae. Despite its proven acaricidal activity, little is known about the mechanism of action of thymol in ticks. Thus, the aim of this study was to perform a morpho-histochemical analysis of the synganglion and salivary glands of partially engorged females of the brown dog tick, Rhipicephalus sanguineus sensu lato (s.l.), exposed to thymol at different concentrations. Five groups were established: Control Group I (distilled water), Control Group II (ethanol 30%), Group III (thymol 1.25 mg/mL), Group IV (thymol 2.5 mg/mL) and Group V (thymol 5.0 mg/mL). The females were exposed to the treatments by the immersion method and subsequently kept in a climatic chamber (27 ± 1 °C and relative humidity 80 ± 10%) for five days. After this period, the synganglion and salivary glands were removed, and the hematoxylin/eosin morphological technique was applied. The von Kossa staining method with counterstaining neutral red was performed on the salivary glands. The results showed that females exposed to thymol had damaged synganglia, with pyknotic nuclei and vacuoles in the cortex and subperineurial regions, as well as rupture of the neural lamellae. The salivary glands showed type I acini with a dilated lumen. Cells with extremely vacuolated cytoplasm and fragmented nuclei were observed in type II and III acini. Type II acini of the females exposed to thymol revealed different calcium staining when compared to the Control Groups I and II. We therefore conclude that the salivary glands and synganglion are subject to changes in morphology and calcium levels when exposed to thymol at concentrations of 1.25, 2.5 and 5.0 mg/mL, demonstrating that this monoterpene has acaricidal potential on partially engorged females of R. sanguineus (s.l.).

Toxic effect of commercial formulations of neem oil, Azadirachta indica A. Juss., in pupae and adults of the sugarcane borer, Diatraea saccharalis F. (Lepidoptera: Crambidae)

ABSTRACT: To evaluate the toxic effect of commercial formulations of neem oil, Azadirachta indica A. Juss, pre-pupae (PP), young pupae (YP) and old pupae (OP) of Diatraea saccharalis F. (Lepidoptera: Crambidae) were sprayed with the diluted extract in distilled water at concentrations of 0.0, 0.3, 0.5, 1.0 and 2.0%. The neem extract caused concentration-dependent effects on mortality of pupae, and the pupae that failed to emerge in adults had multiple abnormalities. The longevity of pupae that emerged in adults (YP and OP group) did not differ from the control group. The abnormalities found in adults were related to mortality in all treatments, except at the concentration of 1.0%. Fertility was assessed according to the oviposition of adult females from the YP group that showed no abnormalities, through the evaluation of the number of deposited eggs and the rate of undeveloped eggs. The results showed a reduction in the number of eggs laid and an increase in the percentage of undeveloped eggs. These results show that neem oil has a high potential to control the toughest stage of the sugarcane borer and also reduces the further development. Therefore, commercial formulations of neem oil have a toxic effect on pupae and adults of D. saccharalis.

Ultrastructural analysis of oocytes of Rhipicephalus (Boophilus) annulatus during postengorgement period as a tool to evaluate the cytotoxic effects of amitraz and deltamethrin on the germinative cells

The present study utilizes the ultrastructural analysis of the fully engorged female Rhipicephalus (Boophilus) annulatus ticks, as a tool to evaluate the cytotoxic potential of deltamethrin and amitraz on the germinative cells. The ultrastructural analysis of the ovary of the normal (untreated) R (B.) annulatus revealed, oocytes in different stages of development, attached to the ovary wall by pedicel cells. The attachment site of oocyte to the pedicel cell was characterized by indentations of the plasma membrane. The oocyte was bound by three cell membranes viz., plasma membrane, chorion and basal lamina. The stages of oocytes were differentiated ultrastructurally based on the features of their outer membrane and the number and size of lipid and yolk droplets. Detailed day wise analysis of ultrastructural changes in the ovary during the post-engorgement period revealed the occurrence of the degenerative changes from day five onwards. These appeared first in the oocytes followed by the germinal epithelium. The ovary of ticks treated with methanol (control), revealed similar topographies as that of a normal ovary except for the presence of very few oocytes with ring shaped nucleoli. Ultrastructurally, treatment with deltamethrin produced more prominent and extensive morphological alterations when compared to amitraz. In the case of ticks treated with amitraz, the oocytes of stage IV and V showed wavy and disrupted outer boundaries along with the loss of integrity of the yolk droplets. Uneven nuclear membranes of stage II oocytes and cristolysis of mitochondria of mature oocytes were the other changes noticed. Ticks treated with deltamethrin revealed prominent modifications such as, detachment of the basal lamina, wrinkled boundary, inconsistent nuclear membrane, ring shaped nucleoli and chromatin clumping in the case of the early stage oocytes (I and II), whereas swelling and cristolysis of mitochondria were seen in mature oocytes. The study further indicated that, in addition to the previous proven neurotoxic effects, these compounds act directly on the ovary of tick.

Detrimental effect of deltamethrin on the central nervous system (synganglion) of Rhipicephalus sanguineus ticks

Ticks are ectoparasites of medical and veterinary importance, which transmit many infectious agents, causing significant damage to the hosts. The "dog tick" Rhipicephalus sanguineus is responsible for transmitting several pathogens to dogs, motivating researchers to investigate efficient and sustainable control methods. Currently, chemical acaricides currently in use target the central nervous system (synganglion), which is responsible for controlling all the systemic functions of the ticks. Here, the neurotoxic potential of deltamethrin on the synganglion of unfed R. sanguineus female ticks was investigated. The results showed that the synganglion of the females belonging to the control group presented intact morphological characteristics; however, the ones from the treatment group (exposed to 1.5, 3.12 and 6.25 ppm of deltamethrin) displayed alterations, which were increasingly intense as the concentration increased. Observed alterations were mainly in the cortex region and in the neuropile, indicating that the deltamethrin is neurotoxic.

In vitro activity of 3β-O-tigloylmelianol from Guarea kunthiana A. Juss (Meliaceae) on oogenesis and ecdysis of the cattle tick Rhipicephalus (Boophilus) microplus (Canestrini) (Acari: Ixodidae)

We evaluated the effects of 3β-O-tigloylmelianol from Guarea kunthiana A. Juss (Meliaceae) on oogenesis, as a larvicide and on ecdysis of the larvae and the nymphs of the cattle tick Rhipicephalus (Boophilus) microplus (Canestrini) (Acari: Ixodidae). On the oogenesis' test, 48 engorged females were divided into three groups, evaluated at 24, 48 and 72 h post-treatment. Half of the females were treated with 0.01% 3β-O-tigloylmelianol diluted in distilled water and 5% dimethyl sulfoxide (DMSO), while the other half (controls) were exposed to distilled water and 5% DMSO. After treatment, the ovaries were weighed in order to measure the gonadosomatic index (GSI) and were also subjected to standard histological technical tests. On the larvicide and ecdysis' tests, 3β-O-tigloylmelianol was tested at concentrations of 0.01, 0.005, 0.0025 and 0.00125%. Compared with the controls, there was a reduction of GSI of approximately 50% on the treated group, which started at 48 h post treatment. Overall, the protolimonoid 3β-O-tigloylmelianol has caused a significant reduction in the number of oocytes. It has also caused alteration of the cytoplasmic and germinal vesicle diameters. Morphological changes, such as vacuolization, chorion irregularity which has modified the oocytes' morphology as well as alterations on the yolk's granules were also observed. The compound was not larvicide, however, interfered in the ecdysis of the larvae and the nymphs. This study shows that the protolimonoid 3β-O-tigloylmelianol from G. kunthiana acts on oogenesis and ecdysis of R. (B.) microplus, but not as larvicide, indicating that it acts on the endocrine system of the tick.

Ovary histology and quantification of hemolymph proteins of Rhipicephalus (Boophilus)microplus treated with Melia azedarach

This study aimed to analyze ovary histology and quantify total protein in the hemolymph of Rhipicephalus (Boophilus)microplus females treated with hexane extracts from green fruits of Melia azedarach. Eight engorged females were immersed in the extract at 0.25% concentration, and eight in water containing 5% acetone (control). The females were dissected 72 hours after treatment, and the ovaries were weighed and subjected to standard histological techniques. The total protein concentration was measured in the hemolymph of 200 females, of which 100 were treated as described above and 100 served as a control. In the treated group, ovary weight reduction and predominance of immature oocytes were observed. In addition, there were decreases in the diameters of the cytoplasm and germ vesicle of the oocytes in the treated group, compared with the controls. The protein concentration in the hemolymph was higher in the treated group than in the controls. The morphological changes observed in the treated ovaries included: presence of vacuolization; alteration of oocyte morphology, which changed from rounded to elongated; deformation of the chorion; and disorganization of the yolk granules. These results demonstrate the action ofM. azedarach fruit extracts on R.(B.) microplus oogenesis.

A draft of the genome and four transcriptomes of a medicinal and pesticidal angiosperm Azadirachta indica

Background

The Azadirachta indica (neem) tree is a source of a wide number of natural products, including the potent biopesticide azadirachtin. In spite of its widespread applications in agriculture and medicine, the molecular aspects of the biosynthesis of neem terpenoids remain largely unexplored. The current report describes the draft genome and four transcriptomes of A. indica and attempts to contextualise the sequence information in terms of its molecular phylogeny, transcript expression and terpenoid biosynthesis pathways. A. indica is the first member of the family Meliaceae to be sequenced using next generation sequencing approach.

Results

The genome and transcriptomes of A. indica were sequenced using multiple sequencing platforms and libraries. The A. indica genome is AT-rich, bears few repetitive DNA elements and comprises about 20,000 genes. The molecular phylogenetic analyses grouped A. indica together with Citrus sinensis from the Rutaceae family validating its conventional taxonomic classification. Comparative transcript expression analysis showed either exclusive or enhanced expression of known genes involved in neem terpenoid biosynthesis pathways compared to other sequenced angiosperms. Genome and transcriptome analyses in A. indica led to the identification of repeat elements, nucleotide composition and expression profiles of genes in various organs.

Conclusions

This study on A. indica genome and transcriptomes will provide a model for characterization of metabolic pathways involved in synthesis of bioactive compounds, comparative evolutionary studies among various Meliaceae family members and help annotate their genomes. A better understanding of molecular pathways involved in the azadirachtin synthesis in A. indica will pave ways for bulk production of environment friendly biopesticides.