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Localisation of lichen secondary metabolites in Cladonia foliacea thallus presented in light microscopic views.a Cortical layer of thickened hyphae with larger (near the surface) and smaller (between the thickened hyphae) yellow UA crystals (see arrows) in water; FA crystals (see arrows) b on lower surface medullary hyphae stained orange, c on hyphae in photosynthetic layer (near algae) and d on hyphae in photosynthetic (ph) and medullary (med) layer stained strongly orange-red by p-phenylenediamine. Scales: a = 50 µm, b, c = 20 µm, d = 10 µm. Micrographs: E. Farkas
Source publication
Lichen specific metabolites (LSMs) have interesting biological activities and quantitative variations may be present intraspecifically. For example, variations in medullary fumarprotocetraric acid (FA) and cortical usnic acid (UA) were observed in the lichen Cladonia foliacea, but the mechanism of variation is not well understood. The current study...
Citations
... Willd. is widely distributed over Europe and relatively frequent in Hungarian lowlands and low elevation mountain rocky grasslands (Wirth et al. 2013) (Fig. 1). It contains two major LSMs (usnic acid and fumarprotocetraric acid) in known concentrations (for usnic acid ranging from 6.88 to 34.27 mg/g dry weight and fumarprotocetraric acid from 1.44 to 9.87 mg/g dry weight - Farkas et al. 2020Farkas et al. , 2024. These metabolites protect the photobionts against harmful UV-and solar radiation (Nguyen et al. 2013), furthermore they have various bioactive roles (Molnár and Farkas 2010), e.g. ...
... However, Emmerich et al. (1993) found significantly different toxicity and antifeedant activity in the larvae of a herbivorous insect (Spodoptera littoralis Boisduval), since the (-)-usnic acid was found to be almost 10-times more effective than the (+)-usnic acid. It was known from 2004 (Bézivin et al. 2004), that C. foliacea produces (-)-usnic acid and it was confirmed that the Hungarian populations also contain this isomer (Farkas et al. 2024) in additionally to fumarprotocetraric acid and 9′-(O-methyl)protocetraric acid. In agreement with Galanty et al. (2019) the study of the usnic acid enantiomers, consequently the (-)-usnic acid enantiomer containing lichen C. foliacea seems to be promising. ...
... The current study did not focus on measuring the amount of the secondary metabolites in C. foliacea since it was initially determined by Farkas et al. (2020Farkas et al. ( , 2024 from samples obtained from the same location of Tece, Vácrátót, Hungary. Use of acetone and 2% food dye as negative control did not cause high mortalities of mosquitoes to warrant discarding any of the test results during the bioassay tests. ...
Plasmodium falciparum is primarily transmitted by Anopheles gambiae . Malaria caused by Plasmodium falciparum is a major public health issue in western Kenya and sub-Saharan Africa, accounting for 90% of malaria deaths. The primary methods of malaria prevention are indoor residual spraying and the use of insecticide-treated nets. These tools face challenges such as mosquito resistance to insecticides as well as their toxic effect to the non-target organism, therefore this study aims to explore the application of lichen secondary metabolites as potential oral biological insecticides by assessing mosquito mortality in varying concentrations. Lichen secondary metabolites were extracted from Cladonia foliacea thalli. Bioassay experiments were conducted on A. gambiae Kisumu strain mosquitoes. Mortality rates were measured after ingesting sugar bait and lichen extracts in different concentrations. Three test replicates and negative control were used, with mortality measured after 4, 24, 48, and 72 hours. Analysis using three-way analysis of variance with twoway interactions was performed using R program to determine the effect of different lichen extract concentrations, time of exposures and mosquito sex on mortality. Our results showed that the ingestion of C. foliacea extract at 50 mg/ml and a post-exposure period of 24 to 48 hours had a maximum effect on the mortality rate of targeted male and female A. gambiae . No statistical difference was found between male and female mosquitoes in mortality. Our study confirms firstly that the extract of C. foliacea is a promising oral toxic agent against adult malaria vector A. gambiae .
... They are known to produce over 1000 unique secondary metabolites. The amount of usnic acid produced by lichens varies and factors such as the algal partner and season have been shown to have a significant relationship [46,47]. These metabolites exhibit various biological activities that include insecticidal bait for the control of malaria vectors. ...
Background
Despite the application of various tools for the control of vectors of Plasmodium falciparum, malaria remains the major killer disease in sub-Saharan Africa accounting for up to 90% of deaths due to the disease. Due to limitations of the useage of chemical insecticides such as resistance, negative impact on the environment and to nontarget organisms, the World Health Organization (WHO) requires that affected countries find alternative vector control tools. This study evaluated the effectiveness of ( +)-usnic acid (UA) as an insecticide through oral administration to male and female Anopheles gambiae as an alternative or additional active ingredient to be used in toxic sugar bait.
Methods
( +)-usnic acid was diluted using acetone at 5, 10, and 15 mg/ml concentrations in three replicates. A 5 ml mixture of 2% food dye and 10% sugar using chlorine-free water mixed with the dilutions of the ( +)-usnic acid and negative control was made containing 2% food dye and 10% sugar solution. The preparations were soaked on a ball of cotton wool and placed over the net of a cup. 5 male and 5 non-blood-fed female newly hatched starved An. gambiae Kisumu strain were introduced together into a cup and monitored for knockdown and mortalities after 4, 24 48, and 72 h. The data were analysed using a multiple linear regression model using the lm function, a base R function and a posthoc test were conducted on the significant main effects and interaction terms using the emmeans function from the emmeans R package. All analyses were performed in RStudio using base R (version 4.3.3).
Results
There was high mortality of both male and female An. gambiae after ingestion of the toxic sugar bait. 15 mg/ml usnic acid caused the highest mortality (50%) within the first 4 h compared to 5 and 10 mg/ml ( +)-UA. There was a decline in the mortality rate with increased exposure time from 24 to 72 h, however, there was a significant difference in mortality at 5, 10 and 15 mg/ml. Acute toxicity was associated with ingestion of 15 mg/ml after 24 h. 72 h post-mortality was lower in all concentrations than in the control. High mortality was observed among females over the first 4 h (60%) compared to males (40%) due to higher feeding rate of the toxic agent. The proportion of dead males and females was equal after 24 h while after 48 h, the proportion of dead males was high.There was a significantly lower mortality rate after 72 h for both males and females (0 to 13.3%). Compared to all the treatments, high mortality of males was observed.
Conclusions
The results of this study indicate that ( +)-UA when administered as oral sugar bait to An. gambiae has insecticidal properties and is a suitable ingredient to be used as a toxic agent in the novel attractive toxic sugar bait for the control of malaria vectors. ( +)-UA may be an alternative active ingredient as toxic bait in the effort to reduce and eliminate the transmission of Plasmodium falciparum in Africa.
