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Toxicity of microcystin-LR, isolated from Microcystis aeruginosa, against various insect species
1Department of Agricultural and Environmental Science, University of Newcastle upon Tyne, U.K.
Abstract:
Microcystin-LR (MC-LR), isolated from the cyanobacterium Microcystis aeruginosa Kuetzing emend. Elenkin strain CCAP 1450/4 was tested for biological activity against four species of insect and the invertebrate Artemia salina. The efficacy of pesticidal activity was compared with various insecticides. The 24 hr LD50 value for third instar diamond-backed moth, Plutella xylostella, on ingestion from a treated leaf surface was 1.0 micrograms cm2, compared with a 72 hr LD50 value for rotenone of 2.0 micrograms cm-2. The 24 hr LD50 values of MC-LR and malathion on intrathoracic injection into adult house flies (Musca domestica) were 0.5 and 3.7 mg kg-1, respectively. MC-LR had no effect on M. domestica when applied topically at dosages up to 32 mg kg-1. MC-LR and malathion gave 24 hr LD50 values of 4.7 and 13.1 mg kg-1, respectively when injected into third instar cotton leafworm (Spodoptera littoralis). In fourth instar cabbage white butterfly larvae (Pieris brassicae) MC-LR injected gave 24 and 48 hr LD50 values of 3.9 and 1.9 mg kg-1, respectively, whilst the 24 and 48 hr LD50 values for carbofuran were 0.4 and 0.3 mg kg-1, respectively. An immersion bioassay with 1-day-old brine shrimp larvae (Artemia salina) gave 24 hr LD50 values of 3.8 micrograms ml-1 for MC-LR and 1.8 micrograms ml-1 for carbofuran. MC-LR has appreciable insect toxicity, comparable to the three insecticides tested. The toxin look 24-48 hr to exert its full lethal effect in insects, much longer than the 1-3 hr it takes in mammals. The potential use of MC-LR as an insecticide is discussed.
Insights
Microcystin-LR (MC-LR), a toxin from cyanobacteria, shows significant insecticidal activity comparable to synthetic insecticides. While slower-acting in insects than mammals, MC-LR demonstrates potential as a novel biopesticide.
Area of Science:
- Environmental Science
- Toxicology
- Biotechnology
Background:
- Cyanobacteria, such as Microcystis aeruginosa, produce toxins like Microcystin-LR (MC-LR).
- The biological activity and potential applications of MC-LR beyond its known mammalian toxicity are not fully understood.
Purpose of the Study:
- To evaluate the insecticidal and pesticidal activity of Microcystin-LR (MC-LR).
- To compare the efficacy of MC-LR against common insecticides across various insect species and an invertebrate model.
Main Methods:
- MC-LR was isolated from Microcystis aeruginosa.
- Biological activity was tested against Plutella xylostella, Musca domestica, Spodoptera littoralis, Pieris brassicae, and Artemia salina.
- LD50 values were determined for MC-LR and reference insecticides (rotenone, malathion, carbofuran) using different exposure routes (ingestion, injection, topical application, immersion).
Main Results:
- MC-LR exhibited significant insect toxicity, with 24-hour LD50 values comparable to or better than tested insecticides for certain species and exposure routes.
- For instance, the 24-hour LD50 for MC-LR against Plutella xylostella via ingestion was 1.0 µg/cm², and against Musca domestica via injection was 0.5 mg/kg.
- MC-LR showed no topical toxicity on Musca domestica and required 24-48 hours to achieve lethal effects in insects, unlike the 1-3 hours in mammals.
Conclusions:
- Microcystin-LR possesses considerable insecticidal properties, demonstrating efficacy comparable to established insecticides.
- The slower action in insects suggests a different toxicological mechanism compared to mammals.
- MC-LR presents potential as a novel biopesticide, warranting further investigation into its application and ecological impact.
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