Katinka Pålsson

Evaluation of extracts and oils of mosquito (Diptera: Culicidae) repellent plants from Sweden and Guinea-Bissau.

Abstract In laboratory tests, ethyl acetate extracts of Hyptis suaveolens Poit. from Guinea-Bissau and Rhododendon tomentosum (Stokes) H. Harmaja (formerly Ledum palustre L.) and Myrica gale L. significantly reduced probing activity of Aedes aegypti (L.). In the field in southern Sweden, extracts of leaves of R. tomentosum, M. gale, and Achillea millefolium L. significantly reduced biting by Aedes mosquitoes. Volatile compounds from M. gale, R. tomentosum, A. millefolium, and H. suaveolens were collected by solid phase microextraction (SPME). Alternatively, compounds in the plants were subjected to extraction by organic solvents of different polarities or by steam distillation and collection by SPME. Compounds collected were identified by gas chromatography-mass spectrometry. Leaves of H. suaveolens contained mainly β-caryophyllene, bergamotene, and terpinolene. The volatile fraction of an ethyl acetate extract of H. suaveolens was collected by SPME and included β-caryophyllene, (−)-sabinene, β-pinene, limonene, α-pinene, and bergamotene. The main volatiles detected were α-pinene, α-phellandrene, myrcene, and limonene from M. gale leaves or inflorescences; p-cymene, sabinene, and terpinyl acetate from leaves of R. tomentosum; and (−)-germacrene D, β-pinene, sabinene, and α-pinene from A. millefolium leaves or inflorescences. The selected plant species contained numerous volatiles known to have insecticidal, acaricidal, “pesticidal,” and/or insect repellent properties.

Evaluation of extracts and oils of tick‐repellent plants from Sweden

Abstract.  Leaves of Myrica gale Linnaeus (Myricaceae), Rhododendron tomentosum (Stokes) H. Harmaja (formerly Ledum palustre Linnaeus: Ericaceae) and Artemisia absinthium Linnaeus (Asteraceae) were extracted with organic solvents of different polarities and the essential oils of leaves were obtained by steam distillation. The extracts or oils were tested in the laboratory for repellency against host‐seeking nymphs of Ixodes ricinus Linnaeus (Acari: Ixodidae). Rhododendron tomentosum oil, 10%, diluted in acetone, exhibited 95% repellency; R. tomentosum and A. absinthium extracts in ethyl acetate, > 70% repellency; A. absinthium extract in hexane, ∼62% repellency; and M. gale oil, 10%, ∼50% repellency on I. ricinus nymphs. Compounds in the leaf extracts or in the oils were collected by solid phase microextraction (SPME) and identified by gas chromatography–mass spectrometry (GC–MS) and/or MS. Characteristic volatiles detected from oil or extract of M. gale were the monoterpenes 1,8‐cineole, α‐terpineol, 4‐terpineol and thujenol; and of R. tomentosum myrcene and palustrol. Characteristic volatiles from leaf extracts of A. absinthium were sabinene, oxygenated monoterpenes, e.g. thujenol and linalool, and geranyl acetate. Each plant species synthesized numerous volatiles known to exhibit acaricidal, insecticidal, ‘pesticidal’ and/or arthropod repellent properties. These plants may be useful sources of chemicals for the control of arthropods of medical, veterinary or agricultural importance.

Repellency of Oils of Lemon Eucalyptus, Geranium, and Lavender and the Mosquito Repellent MyggA Natural to Ixodes ricinus (Acari: Ixodidae) in the Laboratory and Field

Abstract MyggA Natural (Bioglan, Lund, Sweden) is a commercially available repellent against blood-feeding arthropods. It contains 30% of lemon-scented eucalyptus, Corymbia citriodora (Hook.) K. D. Hill & L. A. S. Johnson (Myrtaceae), oil with a minimum of 50% p-menthane-3,8-diol. MyggA Natural also contains small amounts of the essential oils of lavender, Lavandula angustifolia Mill. (Lamiaceae), and geranium, Pelargonium graveolens L’Her. (Geraniaceae). In laboratory bioassays, MyggA Natural and C. citriodora oil exhibited 100% repellency against host-seeking nymphs of Ixodes ricinus (L.) (Acari: Ixodidae). Lavender oil and geranium oil, when diluted to 1% in 1,2-propanediol, had weak repellent activities on I. ricinus nymphs, but when diluted to 30% in 1,2-propanediol had 100% repellencies. 1,2-Propanediol (100%) had no significant repellent activity in comparison with that of the control. In field tests in tick-infested areas in central Sweden, tick repellency of MyggA Natural and C. citriodora oil was tested by the blanket-dragging technique for 4 d during a 6-d period. The repellencies (74 and 85%, respectively) on day 1 are similar (89%) to that of blankets treated in a similar manner with 19% diethyl-methyl-benzamide, based on previous work. Repellencies declined significantly from day 1 to day 6 (74 to 45% for MyggA Natural; 85 to 42% for C. citriodora oil).

High Levels of Hybridization between Molecular Forms of Anopheles gambiae from Guinea Bissau

Abstract In the malaria vector Anopheles gambiae Giles sensu stricto, two molecular forms denoted M and S are considered units of incipient speciation within this species. Very low hybrid frequencies and significant genetic differentiation have been found in sympatric M- and S-form populations. We studied the molecular form composition and the degree of genetic differentiation at 15 microsatellites in two samples of An. gambiae collected in two consecutive years from Bissau, Guinea Bissau. High frequencies of M/S hybrids (19–24%) were found in this area. Coincidently, very low levels of genetic differentiation were detected between forms when analysis involved microsatellites mapped at chromosome-3 (mean Fst, 0.000–0.002). The single exception was the X-linked AGXH678, for which high differentiation was measured (Fst, 0.158–0.301). This locus maps near the centromere of chromosome X, a low recombination region in which selection is likely to promote divergence between M and S forms. These results strongly suggest that the degree of isolation between M and S forms, considered the units of incipient speciation within An. gambiae, is not homogenous throughout the species distribution range.

The "far-west" of Anopheles gambiae molecular forms.

The main Afrotropical malaria vector, Anopheles gambiae sensu stricto, is undergoing a process of sympatric ecological diversification leading to at least two incipient species (the M and S molecular forms) showing heterogeneous levels of divergence across the genome. The physically unlinked centromeric regions on all three chromosomes of these closely related taxa contain fixed nucleotide differences which have been found in nearly complete linkage disequilibrium in geographic areas of no or low M-S hybridization. Assays diagnostic for SNP and structural differences between M and S forms in the three centromeric regions were applied in samples from the western extreme of their range of sympatry, the only area where high frequencies of putative M/S hybrids have been reported. The results reveal a level of admixture not observed in the rest of the range. In particular, we found: i) heterozygous genotypes at each marker, although at frequencies lower than expected under panmixia; ii) virtually all possible genotypic combinations between markers on different chromosomes, although genetic association was nevertheless detected; iii) discordant M and S genotypes at two X-linked markers near the centromere, suggestive of introgression and inter-locus recombination. These results could be indicative either of a secondary contact zone between M and S, or of the maintenance of ancestral polymorphisms. This issue and the perspectives opened by these results in the study of the M and S incipient speciation process are discussed.

Tick repellent substances in the essential oil of Tanacetum vulgare

Abstract The repellent effect of the essential oils of flower heads of the aromatic plant tansy, Tanacetum vulgare L. (Asteraceae), originating from Sweden, was tested against host-seeking nymphs of the common tick Ixodes ricinus (L.). The essential oils were obtained by steam distillation (SD) and by using an online solvent extraction separation setup. Further fractionations of the SD oils were obtained by medium-pressure liquid chromatography on silica gel. The volatiles of the essential oils and the fractions that exhibited strong tick repellency (90–100%) were collected by solid phase microextraction and identified by gas chromatography-mass spectrometry. The chemical analyses of the oils show that the populations of T. vulgare from Uppsala and Stockholm may represent different chemotypes, but that they exhibited similar tick repellency. Main volatiles detected from oils of T. vulgare collected at Uppsala were &agr;-pinene (27%), &bgr;-pinene (11%), pinocamphone (11%), 1,3,3-trimethylcyclohex-1-ene-4-carboxaldehyde (11%), and 1,8-cineole (10%). In the sample collected in Stockholm, the main components were &bgr;-thujone (39%) and camphor (23%) followed by &agr;-thujone (11%) and 1,8-cineole (8%). When constituents in the oils, e.g., &agr;-terpineol, 4-terpineol, &agr; + &bgr;-thujone, 1,8-cineol, verbenol, and verbenone, were tested separately (each diluted 0.5%, vol:vol), 64–72% tick repellency was obtained.

Endophilic Anopheles mosquitoes in Guinea Bissau, West Africa in relation to human housing conditions

Abstract Environmental risk factors associated with increased malaria mosquito (Anopheles) abundance indoors were studied in a suburban area, Antula, of Guinea Bissau, during the rainy seasons of 1993–1995. All bedrooms in 30 houses were searched for resting mosquitoes three times each year. The most abundant mosquito was An. gambiae s.s. Significantly greater numbers of resting mosquitoes were present in rooms with open eaves and in houses with a well on the compound. Pigs were the most common domestic animals in Antula. Presence of pigs in a house was associated with increased mosquito abundance in the bedrooms of the same house. The abundance of female mosquitoes also increased with increasing human biomass per square meter of bedroom area.

Botanical Repellents and Pesticides Traditionally Used Against Hematophagous Invertebrates in Lao People’s Democratic Republic: A Comparative Study of Plants Used in 66 Villages

ABSTRACT Hematophagous parasites such as leeches, ticks, mites, lice, bedbugs, mosquitoes, and myiasis-producing fly larvae are common health problems in Lao Peoples Democratic Republic. Several arthropod-borne infections, e.g., malaria, dengue fever, and Japanese encephalitis, are endemic there. Effective vector control methods including the use of pesticides, insecticide-treated bed nets, and synthetic and plant-based repellents are important means of control against such invertebrates and the pathogens they may transmit or directly cause. In this study, we documented traditional knowledge on plants that are used to repel or kill hematophagous arthropods, including mosquitoes, bedbugs, human lice, mites and ticks, fly larvae, and blood-sucking leeches. Structured interviews were carried out in 66 villages comprising 17 ethnic groups, covering a range of cultures, throughout Lao Peoples Democratic Republic. A total of 92 plant species was recorded as traditional repellents (including plants for pesticidal usages) in 123 different plant-ectoparasite combinations. The number and species of plants, and animal taxa repelled (or killed) per plant species differed per region, village, and ethnic group. Traditional use was confirmed in the scientific literature for 74 of these plant species, and for an additional 13 species using literature on closely related species. The use of botanical repellents and pesticides from many plant species is common and widespread in the Lao countryside. In the future, the identification of the active components in certain plants to develop more optimal, inexpensive repellents, insecticides, acaricides, or antileech compounds as alternatives to synthetic repellents/pesticides against blood-feeding insects, ticks, mites, and leeches is warranted.

Chemical Composition and Repellency of Essential Oils from Four Medicinal Plants Against Ixodes ricinus Nymphs (Acari: Ixodidae)

ABSTRACT In our search for effective tick repellents from plant origin, we investigated the effect of essential oils of four medicinal and culinary plants belonging to the family Lamiaceae on nymphs of the tick Ixodesricinus (L.). The essential oils of the dry leaves of Rosmarinus officinalis (Rosemary) (L.), Mentha spicata (Spearmint) (L.), Origanum majorana (Majoram) (L.), and Ocimum basilicum (Basil) (L.) were isolated by steam distillation and 15 µg/cm2 concentration of oils was tested against ticks in a laboratory bioassay. The oils of R. officinalis, M. spicata, and O. majorana showed strong repellency against the ticks 100, 93.2, and 84.3%, respectively, whereas O. basilicum only showed 64.5% repellency. When tested in the field, the oils of R. officinalis and M. spicata showed 68.3 and 59.4% repellency at a concentration of 6.5 µg/cm2 on the test cloths. The oils were analyzed by gas chromatography mass spectrometry and the major compounds from the most repellent oils were 1,8-cineole, camphor, linalool, 4-terpineol, borneol, and carvone.

Mosquito (Diptera: Culicidae) Repellency Field Tests of Essential Oils from Plants Traditionally used in Laos

ABSTRACT Essential oils of Hyptis suaveolens (Lamiaceae), Croton roxburghii (Euphorbiaceae), and Litsea cubeba (Lauraceae) were tested in the field near Vientiane city, Lao PDR, on humans for repellent activity against mosquitoes. Landing mosquitoes were collected and later identified. The most abundant mosquitoes captured belonged to the genera Armigeres, Culex, and Aedes. All the plant oils tested at concentrations of 1.7 µg/cm2, 3.3 µg/cm2, and 6.3 µg/cm2 were significantly more mosquito repellent than the negative control. Croton oil was significantly repellent against mosquitoes of the three genera at the highest (6.3 µg/cm2) concentration tested. Litsea oil was significantly repellent against Annigeres at all (1.7 µg/cm2, 3.3 µg/cm2, and 6.3 µg/cm2) concentrations tested. Hyptis oil was significantly repellent against Armigeres at 3.3 µg/cm2 and 6.3 µg/cm2 and against Culex at 1.7 µg/cm2 and 6.3 µg/cm2. The oils were analyzed for chemical content of volatiles, mainly terpenes. Main constituents were &bgr;-pinene, sabinene, and 1,8-cineol from oils of the green parts of H. suaveolens; &agr;-pinene, &bgr;-pinene, and &agr;-phellandrene from fresh bark of C. roxburghii; and &agr;-pinene, &bgr;-phellandrene, sabinene, and 1,8-cineol from fresh fruits of L. cubeba.