Mosquito repellent attracts Culicoides imicola (Diptera: Ceratopogonidae)

The Ethnopharmacology, Phytochemistry and Bioactivities of the Corymbia Genus (Myrtaceae)

Plants have been vital to human survival for aeons, especially for their unique medicinal properties. Trees of the Eucalyptus genus are well known for their medicinal properties; however, little is known of the ethnopharmacology and bioactivities of their close relatives in the Corymbia genus. Given the current lack of widespread knowledge of the Corymbia genus, this review aims to provide the first summary of the ethnopharmacology, phytochemistry and bioactivities of this genus. The Scopus, Web of Science, PubMed and Google Scholar databases were searched to identify research articles on the biological activities, phytochemistry and ethnomedical uses of Corymbia species. Of the 115 Corymbia species known, 14 species were found to have ethnomedical uses for the leaves, kino and/or bark. Analysis of the references obtained for these 14 Corymbia spp. revealed that the essential oils, crude extracts and compounds isolated from these species possess an array of biological activities including anti-bacterial, anti-fungal, anti-protozoal, anti-viral, larvicidal, insecticidal, acaricidal, anti-inflammatory, anti-oxidant, anti-cancer and anti-diabetic activities, highlighting the potential for this under-studied genus to provide lead compounds and treatments for a host of medical conditions.

Comparison of the efficiency of the Onderstepoort- and Centres for Disease Control ultraviolet light traps for the collection of livestock associated Culicoides species in South Africa

Comparative monitoring of the abundance and distribution of Culicoides biting midges (Diptera: Ceratopogonidae), the biological vectors of the causative agents of several diseases of global veterinary importance, will be crucial in determining the risk of disease outbreak and spread. Ultraviolet (UV) suction traps have become the most frequent method used for the monitoring of Culicoides diversity and abundance. The current study compared the trapping efficiency of the two most used UV suction light traps, i.e., the Onderstepoort (OP)- and the Centres for Disease Control trap, for the collection of livestock associated Culicoides species in South Africa. The study confirmed the superiority of the OP trap and indicated a correlation in species composition and age grading results as determine with the two trap types. Substantial variations in the comparative trap efficiency, as found between areas and sites within an area, suggest that a universal conversion factor between the two trap types may not be advisable as it is unclear to what extent species composition and environmental factors may influence the conversion factor. Light traps, independent of trap model, can be considered acceptable for determining the serial comparison of population numbers for seasonal fluctuation and species abundance in distribution surveys.

Spatial repellency and vapour toxicity of transfluthrin against the biting midges Culicoides nubeculosus and C. sonorensis (Ceratopogonidae)

Biting midges (Diptera; Ceratopogonidae; Culicoides spp.) are biological vectors of disease agents, and they cause nuisance and insect bite hypersensitivity. Currently there are no effective means to control biting midges as screening is impractical and the application of insecticides or repellents is of limited efficacy. Spatial repellents have the advantage over contact repellents that they can create a vector-free environment. Studies have shown the efficacy of spatial repellents to protect humans against mosquitoes, also outdoors, but no data are available for biting midges. We tested the spatial repellency and toxicity (knockdown effect) of the volatile pyrethroid transfluthrin against the laboratory-reared biting midges Culicoides nubeculosus (Meigen) and Culicoides sonorensis (Wirth and Jones) and the mosquito Aedes aegypti (Linnaeus) in a high-throughput tube setup. Observations were made 15, 30 and 60 min. after application of the repellent. In addition to transfluthrin, the non-volatile pyrethroid permethrin and DEET, the gold standard of repellents, were included. Spatial repellency by transfluthrin was observed against both biting midge species and Ae. aegypti, already at the first observation after 15 min. and at much lower concentrations than DEET. Permethrin was spatially repellent only to C. sonorensis at the highest concentration tested (10 μg/cm²). Knockdown of biting midges and mosquitoes by transfluthrin, both by vapour or contact toxicity, was observed even at low concentrations. DEET had little to no effect on the knockdown of the insects, neither by direct contact nor vapour toxicity, while permethrin caused a high proportion of knockdown when direct contact was possible. In case these results can be confirmed in field experiments, spatial repellents could become a novel tool in integrated control programmes to reduce biting by Culicoides spp.

Laboratory and field evaluations of chemical and plant-derived potential repellents against Culicoides biting midges in northern Spain

The efficacy of 23 compounds in repelling Culicoides biting midges (Diptera: Ceratopogonidae), particularly Culicoides obsoletus (Meigen) females, was determined by means of a Y-tube olfactometer. The 10 most effective compounds were further evaluated in landing bioassays. The six most promising compounds (including chemical and plant-derived repellents) were evaluated at 10% and 25% concentrations in field assays using Centers for Disease Control (CDC) light traps. At least three compounds showed promising results against Culicoides biting midges with the methodologies used. Whereas olfactometer assays indicated DEET at 1 µg/µL to be the most effective repellent, filter paper landing bioassays showed plant-derived oils to be better. Light traps fitted with polyester mesh impregnated with a mixture of octanoic, decanoic and nonanoic fatty acids at 10% and 25% concentrations collected 2.2 and 3.6 times fewer midges than control traps and were as effective as DEET, which is presently considered the reference standard insect repellent. The best plant-derived product was lemon eucalyptus oil. Although these have been reported as safe potential repellents, the present results indicate DEET and the mixture of organic fatty acids to be superior and longer lasting.

The acaricidal efficacy of aqueous neem extract and ivermectin against Sarcoptes scabiei var. cuniculi in experimentally infested rabbits

Sarcoptes scabiei var. cuniculi is one of the most important veterinary ectoparasites in rabbits and results in considerable loss of weight, productivity, and wool quality. The acaricidal activity of aqueous leaf extract of neem (CAN) and ivermectin (IVR) were evaluated in vitro and in vivo against S. scabiei var. cuniculi. Rabbits were classified into four groups (ten rabbits each). The first group (group 1) was designated as the negative control group. Each rabbit of the other groups was experimentally infested with 50 mites. One month post-infestation, the second group (group 2) was not treated and taken into account as the positive control group. The third group (group 3) was subcutaneously injected with 1 % IVR (200 μg/kg body weight, three times within a week interval). The fourth group (group 4) was treated topically with CAN (25 %) every 3 days for three consecutive weeks. Index scoring of lesions was described weekly. The number of live mites (larvae, nymphs, and adults) on each rabbit was counted on the 14th, 28th, and 42th day post-treatment (PT). Blood samples were taken 28 and 42 days PT for estimation of some chemical parameters. The body weight and cumulative body weight gain were recoded 14, 28, and 42 days PT. CAN (40 %) was highly efficacious against larvae of S. scabiei var. cuniculi as 100 % mortality was reached 24 h PT. On the other hand, all treated mites with CAN (20 %) and IVR died 48 h PT. The lethal values of CAN (LC50, LC90, LC95, and LC99) were 7.496, 14.67, 17.75, and 25.37 %, respectively, 48 h PT. Lesion scoring in groups 3 and 4 were significantly decreased (P ≤ 0.05), reaching 0.20 and 0.40, respectively, when compared with that of group 2 (4.00), 42 days PT. Twenty-eight days PT, the reduction percentages of mites infesting rabbits were 93.38 and 93.09 % for IVR and CAN, respectively. However, complete mite reduction was reached 42 days PT. Rabbits treated with CAN did not show signs of restlessness or irritation, respiratory signs, or inflammation on the eye and/or skin at the time of application or afterwards. Regarding biochemical analysis, the levels of aspartate aminotransferase, alanine aminotransferase, creatinine, and total cholesterol in rabbits treated with CAN were decreased significantly (P ≤ 0.05) than those of rabbits of the positive control group and those treated with IVR. On the other hand, the levels of total protein, albumin, and globulin of rabbits in group 4 were significantly (P ≤ 0.05) increased when compared with the corresponding values of groups 2 and 3. The body weight and cumulative body weight gain of rabbits treated with CAN were significantly increased (P ≤ 0.05) when compared with such values of groups 2 and 3, 28 and 42 days PT. The present data indicated that CAN had in vitro and in vivo acaricidal efficiency similar to that of IVR and improved the performance of rabbits without inducing adverse effects on treated rabbits; consequently, CAN could be suitable as a promising alternative acaricide for veterinary use.

Essential oils in insect control: low-risk products in a high-stakes world

In recent years, the use of essential oils (EOs) derived from aromatic plants as low-risk insecticides has increased considerably owing to their popularity with organic growers and environmentally conscious consumers. EOs are easily produced by steam distillation of plant material and contain many volatile, low-molecular-weight terpenes and phenolics. The major plant families from which EOs are extracted include Myrtaceae, Lauraceae, Lamiaceae, and Asteraceae. EOs have repellent, insecticidal, and growth-reducing effects on a variety of insects. They have been used effectively to control preharvest and postharvest phytophagous insects and as insect repellents for biting flies and for home and garden insects. The compounds exert their activities on insects through neurotoxic effects involving several mechanisms, notably through GABA, octopamine synapses, and the inhibition of acetylcholinesterase. With a few exceptions, their mammalian toxicity is low and environmental persistence is short. Registration has been the main bottleneck in putting new products on the market, but more EOs have been approved for use in the United States than elsewhere owing to reduced-risk processes for these materials.

Dihydronepetalactones deter feeding activity by mosquitoes, stable flies, and deer ticks

The essential oil of catmint, Nepeta cataria L., contains nepetalactones, that, on hydrogenation, yield the corresponding dihydronepetalactone (DHN) diastereomers. The DHN diastereomer (4R,4aR,7S,7aS)-4,7-dimethylhexahydrocyclopenta[c]pyran-1(3H)-one, DHN 1) was evaluated as mosquito repellent, as was the mixture of diastereomers {mostly (4S,4aR,7S,7aR)-4,7-dimethylhexahydrocyclopenta[c]pyran-1(3H)-one, DHN 2} present after hydrogenation of catmint oil itself. The repellency of these materials to Aedes aegypti L. and Anopheles albimanus Wiedemann mosquitoes was tested in vitro and found to be comparable to that obtained with the well-known insect repellent active ingredient N,N-diethyl-3-methylbenzamide (DEET). DHN 1 and DHN 2 also repelled the stable fly, Stomoxys calcitrans L., in this study. DHN 1, DHN 2, and p-menthane-3,8-diol (PMD), another natural monoterpenoid repellent, gave comparable levels of repellency against An. albimanus and S. calcitrans. Laboratory testing of DHN 1 and DHN 2 using human subjects with An. albimanus mosquitoes was carried out. Both DHN 1 and DHN 2 at 10% (wt:vol) conferred complete protection from bites for significant periods of time (3.5 and 5 h, respectively), with DHN2 conferring protection statistically equivalent to DEET. The DHN 1 and DHN 2 diastereomers were also efficaceous against black-legged tick (Ixodes scapularis Say) nymphs.

Factors affecting Culicoides species composition and abundance in avian nests

Mechanisms affecting patterns of vector distribution among host individuals may influence the population and evolutionary dynamics of vectors, hosts and the parasites transmitted. We studied the role of different factors affecting the species composition and abundance of Culicoides found in nests of the blue tit (Cyanistes caeruleus). We identified 1531 females and 2 males of 7 different Culicoides species in nests, with C. simulator being the most abundant species, followed by C. kibunensis, C. festivipennis, C. segnis, C. truncorum, C. pictipennis and C. circumscriptus. We conducted a medicationxfumigation experiment randomly assigning bird's nests to different treatments, thereby generating groups of medicated and control pairs breeding in fumigated and control nests. Medicated pairs were injected with the anti-malarial drug Primaquine diluted in saline solution while control pairs were injected with saline solution. The fumigation treatment was carried out using insecticide solution or water for fumigated and control nests respectively. Brood size was the main factor associated with the abundance of biting midges probably because more nestlings may produce higher quantities of vector attractants. In addition, birds medicated against haemoparasites breeding in non-fumigated nests supported a higher abundance of C. festivipennis than the rest of the groups. Also, we found that the fumigation treatment reduced the abundance of engorged Culicoides in both medicated and control nests, thus indicating a reduction of feeding success produced by the insecticide. These results represent the first evidence for the role of different factors in affecting the Culicoides infracommunity in wild avian nests.

Toward development of neem-based repellents against the Scottish Highland biting midge Culicoides impunctatus

Oil of neem, from the tree Azadirachta indica A. Juss (Meliaceae), was evaluated for repellent and antifeedant activity against Culicoides biting midges (Diptera: Ceratopogonidae), by three complementary methods with serial dilutions. Electroantennograms revealed the sensitivity of Culicoides nubeculosus (Meigen) females to neem > or = 0.10%. Culicoides impunctatus Goetghebuer females were repelled by > or = 1% in a Y-tube olfactometer, Using a membrane feeder for wild-caught parous females of C. impunctatus, the proportion blood-feeding was significantly reduced by topical applications of neem oil > or = 0.10% concentrations, with blood-feeding completely prevented by > or =1%. On the basis of these response data, we developed 2% neem-based formulations for personal protection against biting midges.