Various treatments are found to be moderately effective in managing Demodex-related diseases except tea tree oil (TTO) and terpinen-4-ol (T4O), which showed superior miticidal and anti-inflammatory effects in numerous clinical studies. Their possible effects include lowering mite counts, relieving Demodex-related symptoms, and modulating the immune system. This review summarizes the current clinical topical and oral treatments in human demodicosis, their possible mechanisms of action, side-effects and resistance in treating this condition. TTO (especially T4O) is found to be the most effective followed by metronidazole, ivermectin and permethrin in managing the disease. This is because TTO has anti-parasitic, anti-bacterial, anti-fungal, anti-inflammatory and wound-healing effects. Furthermore, nanoTTO can even release its contents into fungus and Pseudomonas biofilms. Combinations of different treatments are occasionally needed for refractory cases, especially for individuals with underlying genetic predisposal or are immuno-compromised. Although the current treatments show efficacy in controlling the Demodex mite population and the related symptoms, further research needs to be focused on the efficacy and drug delivery technology in order to develop alternative treatments with better side-effects profiles, less toxicity, lower risk of resistance and are more cost-effective.

The occurrence of pesticidal pollution in the environment and the resistance in the mosquito species makes an urge for the safer and an effective pesticide. Permethrin, a poorly water-soluble pyrethroid pesticide, was formulated into a hydrodispersible nanopowder through rapid solvent evaporation of pesticide-loaded oil in water microemulsion. Stability studies confirmed that the nanopermethrin dispersion was stable in paddy field water for 5 days with the mean particle sizes of 175.3 ± 0.75 nm and zeta potential of −30.6 ± 0.62 mV. The instability rate of the nanopermethrin particles was greater in alkaline (pH 10) medium when compared with the neutral (pH 7) and acidic (pH 4) dispersion medium. The colloidal dispersion at 45°C was found to be less stable compared with the dispersions at 25 and 5°C. The 12- and 24-h lethal indices (LC50) for nanopermethrin were found to be 0.057 and 0.014 mg l−1, respectively. These results were corroborative with the severity of damages observed in the mosquito larvae manifested in epithelial cells and the evacuation of the midgut contents. Further, the results were substantiated by the decrease in cellular biomolecules and biomarker enzyme activity in nanopermethrin treated larvae when compared to bulk and control treatment.

The ubiquitous use of pesticides has increased concerns over their direct and indirect effects on disease dynamics. While studies examining the effects of pesticides on host–parasite interactions have largely focused on how pesticides influence the host, few studies have considered the effects of pesticides on parasites. We investigated the toxicity of six common insecticides at six environmentally-relevant concentrations to cercariae of the trematode Echinoparyphium from two populations. All six insecticides reduced the survival of cercariae (overall difference between mortality in control vs pesticide exposure = 86·2 ± 8·7%) but not in a predictable dose-dependent manner. These results suggest that Echinoparyphium are sensitive to a broad range of insecticides commonly used in the USA. The lack of a clear dose-dependent response in Echinoparyphium highlights the potential limitations of toxicity assays in predicting pesticide toxicity to parasites. Finally, population-level variation in cercarial susceptibility to pesticides underscores the importance of accounting for population variation as overlooking this variation can limit our ability to predict toxicity in nature. Collectively, this work demonstrates that consideration of pesticide toxicity to parasites is important to understanding how pesticides ultimately shape disease dynamics in nature.

Control of the malaria vector An. gambiae is still largely obtained through chemical intervention using pyrethroids, such as permethrin. However, strains of An. gambiae that are resistant to the toxic effects of pyrethroids have become widespread in several endemic areas over the last decade. The objective of this study was to assess differences in five life-history traits (larval developmental time and the body weight, fecundity, hatch rate, and longevity of adult females) and energy metabolism between a strain of An. gambiae that is resistant to permethrin (RSP), due to knockdown resistance and enhanced metabolic detoxification, and a permethrin susceptible strain reared under laboratory conditions. We also quantified the expression levels of five antioxidant enzyme genes: GSTe3, CAT, GPXH1, SOD1, and SOD2. We found that the RSP strain had a longer developmental time than the susceptible strain. Additionally, RSP adult females had higher wet body weight and increased water and glycogen levels. Compared to permethrin susceptible females, RSP females displayed reduced metabolic rate and mitochondrial coupling efficiency and higher mitochondrial ROS production. Furthermore, despite higher levels of GSTe3 and CAT transcripts, RSP females had a shorter adult life span than susceptible females. Collectively, these results suggest that permethrin resistance alleles might affect energy metabolism, oxidative stress, and adult survival of An. gambiae. However, because the strains used in this study differ in their genetic backgrounds, the results need to be interpreted with caution and replicated in other strains to have significant implications for malaria transmission and vector control.

Pyrethroids are the insecticides of choice for the treatment of bednets for malaria control. Pyrethroid resistance in Anopheles spp. vectors may adversely impact malaria control measures, and therefore it is important to know the initial level of pyrethroid resistance before pyrethroid-treated bednets are introduced. Furthermore, a search for replacement insecticides is necessary to manage any eventual high-resistance levels to pyrethroid insecticides that may affect the effectiveness of treated bednets. This study reports on the susceptibility of Anopheles gambiae s.s. exposed for 1 h to the pyrethroid insecticide permethrin and the carbamate insecticide propoxur, at eight localities in the Greater Accra region of Ghana. The observed mortality rates ranged between 21–92% and 92–100% to permethrin and propoxur, respectively. The results also showed a reduction in the knockdown time (KD50 and KD95) in propoxur (mean KD50 = 20 min and mean KD95 = 31 min) when compared with permethrin (mean KD50 = 47 min and mean KD95 = 87 min). The results suggest that permethrin may not be effective in all areas. Where pyrethroid resistance is a problem, propoxur could be an alternative for indoor residual spraying and for insecticide-treated materials such as curtains and eave screens.

When strong directional selection acts on a trait, the spatial distribution of phenotypes may reflect effects of selection, as well as the spread of favoured genotypes by gene flow. Here we investigate the relative impact of these factors by assessing resistance to synthetic pyrethroids in a 12-year study of diamondback moth, Plutella xylostella, from southern Australia. We estimated resistance levels in populations from brassicaceous weeds, canola, forage crops and vegetables. Differences in resistance among local populations sampled repeatedly were stable over several years. Levels were lowest in samples from weeds and highest in vegetables. Resistance in canola samples increased over time as insecticide use increased. There was no evidence that selection in one area influenced resistance in adjacent areas. Microsatellite variation from 13 populations showed a low level of genetic variation among populations, with an AMOVA indicating that population only accounted for 0.25% of the molecular variation. This compared to an estimate of 13.8% of variation accounted for by the resistance trait. Results suggest that local selection rather than gene flow of resistance alleles dictated variation in resistance across populations. Therefore, regional resistance management strategies may not limit resistance evolution.

—In order to evaluate the effect of permethrin-treated wall cloth against phlebotomine sandflies, a study lasting 26 months (February 1989 to March 1991) was conducted in Marigat Location of Baringo District, Kenya, an endemic focus of both visceral and cutaneous leishmaniases. In six experimental villages, a total of 2000 houses were fitted with cloth made of cotton and impregnated with permethrin EC 20% at a dosage of 0.5 g/m2 diluted in water. Houses in the two control villages were not fitted with cloths and were located 1.5 km away from the experimental area. Traps made of clear polythene sheeting were coated with castor oil and placed inside houses to collect endophilic sandflies. In the experimental villages, the permethrin-treated wall cloth (called Mbu cloth) reduced the population of sandflies found inside houses by 52–73%. Phlebotomus martini and P. duboscqi, vectors of visceral and cutaneous leishmaniases, were reduced by 76 and 85% respectively. In the experimental villages, highly significant differences were observed between the average numbers of sandflies collected before deployment of the treated wall cloth and those observed after thethird treatment of the cloth. No major sandfly reduction was observed however, in the control villages. There was also evidence of feeding reduction due to the permethrin.

Ctenocephalides felis adults obtained from young goats belonging to the Faculty of Veterinary Medicine (SUA) were reared in captivity and the offsprings used for testing against permethrin. A total of 1260 fleas were exposed to 0.005% permethrin dust (0.5% a.i. diluted with fine sand) for periods varying from 30 min to 24 hr. Additionally, white rats infested with 2400 fleas were exposed to a similar mixture for 24 hr.

In the first set of tests, 100% mortality was obtained after a 2-hr exposure of the insects to the insecticide. Similarly, in the second set of tests, all the fleas were found dead at the end of 24-hr exposure.

It was generally concluded that permethrin is very effective against this flea species and that it could be used for controlling the ectoparasite in livestock, animal barns and residential houses in the area. It was finally recommended that similar tests with other flea species in the country, especially in plague endemic areas were desirable.

Studies conducted using laboratory and field bioassays showed that cypermethrin (b = −1.691) had a significantly (P < 0.05) higher and longer residual action at 7,14,21 and 28 days after application than did fenvalerate (b = −2.28) and permethrin (b = −1.871) against Dysdercus fasciatus Sign, and D. nigrofasciatus Stal. when coefficient regression analyses were performed. Residual action of fenvalerate and permethrin was regarded as being identical over the same experimental period in the field since their regression coefficients were not significantly (P > 0.05) different from each other.

It was also shown by these studies that the effective interval between applications was 21 days for cypermethrin and 14 days when fenvalerate and permethrin were applied. This finding has important practical implications in the adoption of an integrated approach aimed at minimizing damage to cotton by D. nigrofasciatus.

In North Africa, the potato tubermoth Phthorimaea operculella (Zeller) is an important pest in traditional, non-refrigerated potato stores. A collaborative research programme of the Institut National de la Recherche Agronomique de Tunisie (INRAT) and the International Potato Center (CIP) investigates the relationships between, (a) the dynamics of the field populations, (b) the harvest date, (c) the economic damage in the field, and (d) the subsequent damage in stores under Tunisian conditions. Emphasis was given to the identification of cultural practices that allowed reduction of pesticide applications and to the replacement of the commonly used parathion with less toxic products.

Potato tubermoth control was achieved by applying a synthetic pyrethroid (permethrin) or Bacillus thuringiensis at the beginning of the storage period. The latter, however, seemed to be less effective on tubers with a high initial infestation (over 20%). The studies showed that tuber damage could be avoided by an early harvest and insecticide applications in the field were not indicated.

An integrated control approach including an early harvest date (to reduce initial tuber infestation), and the application of B. thuringiensis or a synthetic pyrethroid is being developed.

Tanzanian strains of Tribolium castaneum (Herbst), Gnatocerus maxillosus (F.), Sitophilus oryzae (L.) and Sitophilus zeamais Motschulsky were confined to maize grain treated with a dilute dust of permethrin at the rates of 1.5, 3.0 and 6.0 ppm active ingredient. The adult mortality and resulting F1 generation were recorded. G. maxillosus was very susceptible to the insecticide and even the lowest dose brought complete control. T. castaneum adults survived all treatments but few F1 were produced. Adult survival of s. oryzae and S. zeamais was progressively reduced by increasing dosage, although S. zeamais was much less susceptible to the treatment than S. oryzae.

The repellency of grain, treated with 3.0 ppm permethrin, to S. oryzae, S. zeamais and T. castaneum was tested in a simple choice chamber. Neither male nor female T. castaneum were repelled but significantly fewer eggs were laid on treated grain. For both Sitophilus spp there was no significant difference between the numbers of females or eggs observed on treated or untreated grain, but males were repelled from permethrin.

The importance of these results is discussed in relation to a recent recommendation that the treatment of shelled grain with 3.0 ppm permethrin should be adopted in Tanzania in order to control Prostephanus truncatus (Horn), a new and serious storage pest.

The corn earworm damage to seven maize cultivars TZB, TZPB, WYI, 096EP6, Farz 25, ‘Kewesoke’ and Local White, was assessed during the early and late cropping seasons of 1980 and 1981 at Ikenne and Ilora located in the rain-forest and derived savanna zones, respectively. The effectiveness of dimethoate and permethrin in controlling the earworms was evaluated. All the cultivars appeared susceptible to earworm infestation in the two ecological zones. Infestation was consistently and significantly higher in the early season and also in the rain-forest zone. It ranged from 71.5 to 86% in the early and from 28 to 36.8% in the late seasons, respectively, at Ikenne. At Ilora, infestation ranged from 53 to 82% and from 20 to 75% in the early and late seasons, respectively. Mussidia nigrivenella and Heliolhis armigera were the dominant species recorded damaging the grains.

Earworm infestation was significantly lower on plots treated wtih three applications of 0.05 and 0.1% a.i. permethrin at weekly intervals than on plots that received the same dosages and sprays of dimethoate and the control. Maize yields were significantly higher on permethrin-treated plots. The lower dosage of permethrin is recommended to reduce chemical residue on maize grains.