https://www.ghdonline.org/uploads/Pyretrhoid_resistance_review-_Ranson_et_al_Trends_in_Parasit_2011.pdf

Pyrethroid resistance in African anopheline mosquitoes: what are the implications for malaria control?

Repellent activity of essential oils: a review.

The African mosquito species Anopheles gambiae sensu lato s.l. and Anopheles funestus rank among the world's most efficient vectors of human malaria. Their unique bionomics, particularly their anthropophilic, endophagic and endophilic characters, guarantee a strong mosquito-host interaction, favorable to malaria transmission. Olfactory cues govern the various behaviors of female mosquitoes and here we review the role of semiochemicals in the life history of African malaria vectors. Recent evidence points towards the existence of human-specific kairomones affecting host-seeking A. gambiae s.l., and efforts are under way to identify the volatiles mediating this behavior. Based on examples from other Culicidae spp., it is argued that there is good reason to assume that mating, sugar feeding, and oviposition behavior in Afrotropical malaria vectors may also be mediated by semiochemicals. It is foreseen that increased knowledge of odor-mediated behaviors will be applied in the development of novel sampling techniques and possibly alternative methods of intervention to control malaria.

Odor-mediated behavior of afrotropical malaria mosquitoes

Insecticide Resistance in African Anopheles Mosquitoes: A Worsening Situation that Needs Urgent Action to Maintain Malaria Control

Plant-based repellents have been used for generations in traditional practice as a personal protection measure against host-seeking mosquitoes. Knowledge on traditional repellent plants obtained through ethnobotanical studies is a valuable resource for the development of new natural products. Recently, commercial repellent products containing plant-based ingredients have gained increasing popularity among consumers, as these are commonly perceived as “safe” in comparison to long-established synthetic repellents although this is sometimes a misconception. To date insufficient studies have followed standard WHO Pesticide Evaluation Scheme guidelines for repellent testing. There is a need for further standardized studies in order to better evaluate repellent compounds and develop new products that offer high repellency as well as good consumer safety. This paper presents a summary of recent information on testing, efficacy and safety of plant-based repellents as well as promising new developments in the field.

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Plant-based insect repellents: a review of their efficacy, development and testing

The aims of the present study in the south-west of the country were to check if local An. gambiae s.s. showed any resistance to pyrethroid insecticides and if so to compare the level of resistance observed with that reported in other countries in West Africa. (authors)

Resistance of the malaria vector Anopheles gambiae s.s. to pyrethroid insecticides, in south-western Nigeria.

En Afrique, les programmes de lutte contre le paludisme resident pour la plupart, dans le traitement de la maladie et la fourniture de moustiquaires traitees aux insecticides. L'impact de ces programmes est reste limite et de nouvelles approches sont preconisees, y compris des strategies de gestion integree du vecteur, en partenariat avec l'industrie. Des etudes sur le moustique ont ete menees pour AngloGold/Ashanti en vue de mettre en place un programme integre de lutte contre le paludisme dans la ville d'extraction d'or d'Obuasi au Ghana. Les vecteurs du paludisme collectes dans les maisons ont ete identifies par especes et par formes moleculaires au moyen de la PCR et testes pour leur resistance aux insecticides en utilisant les dosages standards de l'OMS et les dosages (kdr) d'insensibilite de l'emplacement de la cible moleculaire. Les especes An. funestus s.s.et An. gambiae S et les formes M ont ete identifiees. Les prelevements d'An. gambiae forme S ont montre une resistance au DDT, aux pyrethrinoides et aux carbamates, tandis que An. funestus s'est montre resistant au DDT et aux carbamates. La forme M An. gambiae est apparue en nombre tres peu eleve et leur resistance n'a pas pu etre evaluee de maniere fiable. Le dosage standard de la PCR pour la detection de la mutation kdr chez An. gambiae forme S a montre qu'il y a peu de correlation avec la resistance aux pyrethrinoides. Le sequencage ulterieur du domaine IIS6 contenant la mutation kdr provenant de neuf moustiques survivants a montre que huit d'entre eux etaient homozygotes resistants et un heterozygote. Ceci correspondait aux resultats des dosages et aux etudes anterieures sur le An. gambiae ouest africain, soulevant cependant quelques inquietudes sur la fiabilite du dosage PCR pour la detection de la mutation kdr. A la suite de ces recherches, AngloGold/Ashanti ont mis en place un programme de controle de vecteur, en plus du traitement de prise en charge des cas, integrant la gestion de la resistance aux insecticides en alternant differentes categories d'insecticides en pulverisation dans les maisons, l'approvisionnement en ITNs, le depistage des maisons et la gestion environnementale appropriee, c'est-a-dire la gestion integree du vecteur.

Insecticide resistance in malaria vector mosquitoes in a gold mining town in Ghana and implications for malaria control.

The effect of pyrethroid resistance on the fitness of a laboratory strain of Anopheles funestus originating from southern Mozambique was evaluated by comparing the developmental and reproductive characteristics of a pyrethroid resistant strain with an insecticide susceptible strain. Fitness was evaluated in terms of fecundity, fertility, egg production, developmental time and life stage progression and survival. Of the eggs laid by females of the resistant strain, 81.5% hatched while only 66.9% were recorded in the susceptible strain. The time from egg hatch to adult emergence was longer for the resistant strain (15.9 days) than the susceptible strain (15.2 days). A significantly higher proportion of eggs from the resistant strain (61.6%) survived to adulthood compared with those of the susceptible strain (49%). Fecundity and larval and pupal survival did not differ significantly between strains. Of spermathecae dissected from females of the resistant strain, 56.8% were fertilized compared to 52.6% from the susceptible strain. The proportion of females that successfully produced eggs was 43.3% and 23.3% for the resistant and susceptible strains respectively. Complete failure of larval hatch was recorded in 28.6% of susceptible strain families compared to 7.7% of resistant families. Our results show that pyrethroid resistance in southern African An. funestus does not incur any loss of fitness under laboratory conditions. These results suggest that the removal of pyrethroid insecticide selection pressure may not lead to a regression of resistance alleles in pyrethroid resistant An. funestus populations in southern Africa.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0007485307005317

Relative developmental and reproductive fitness associated with pyrethroid resistance in the major southern African malaria vector, Anopheles funestus

Cyclodiene insecticide resistance in malaria vector mosquitoes of the Anopheles gambiae species complex (Diptera: Culicidae) has been reported previously from several parts of Africa. We report resistance to dieldrin, a cyclodiene, in two laboratory strains of An. gambiae Giles sensu stricto code-named Ian P20 from Nigeria (1979) and CIG from Cote d'Ivoire (1997). Dieldrin resistance levels were high in adult female mosquitoes (40-75% survived exposure to 4% dieldrin for 1 h) and was closely linked with chromosomal paracentric inversion 2La. This inversion did not occur in Hardy-Weinberg proportions, but showed an excess of heterozygotes in both strains, which may account for the high levels of resistance. This linkage also suggests that dieldrin resistance in Ian P20 is dominant. After subsamples of strain Ian P20 were exposed for 1 h to dieldrin 4% or fipronil 2% (discriminating concentrations), the resultant mortality-rates (61% and 65%) were not significantly different. Most survivors after fipronil treatment also survived subsequent exposure to dieldrin (46/50=92%). This apparent cross-resistance between insecticides of two classes (cyclodiene and phenyl pyrazole) has implications for the management of insecticide resistance in wild populations of the An. gambiae complex.

Resistance to dieldrin + fipronil assorts with chromosome inversion 2La in the malaria vector Anopheles gambiae.

Objective To assess the repellency effect of three local plants; fever tea (Lippia javanica), rose geranium (Pelargonium reniforme) and lemon grass (Cymbopogon excavatus) against laboratory reared Anopheles arabiensis mosquitoes Design A laboratory experimental study Setting Mpumalanga Province, South Africa Subjects Three adult male volunteers Main outcome measures Affordable alternatives to synthetic repellents against biting of Anopheles arabiensis mosquitoes Results All three alcohol plant extracts provided significantly more protection (p = 0012) than alcohol control The alcohol plant extract of L javanica provided 767% protection against An arabiensis after a four hour period, and C excavatus and P reniforme provided 667% and 633% protection for three hours, respectively At five hours post application only L javanica alcohol extract provided appreciable protection (593%) against An arabiensis Conclusion The results of this study indicate that L javanica, P reniforme and C excavatus protect against An arabiensis mosquito bites with the repellent effect of L javanica lasting significantly longer than that of the other two plants

R.H. Hunt

Papers

Resistance of the malaria vector Anopheles gambiae s.s. to pyrethroid insecticides, in south-western Nigeria.

Insecticide resistance in malaria vector mosquitoes in a gold mining town in Ghana and implications for malaria control.

Relative developmental and reproductive fitness associated with pyrethroid resistance in the major southern African malaria vector, Anopheles funestus

Resistance to dieldrin + fipronil assorts with chromosome inversion 2La in the malaria vector Anopheles gambiae.

Local plants as repellents against Anopheles arabiensis, in Mpumalanga Province, South Africa.