Potent Antimicrobial and Antimalaria Compound Isolated from Ladybug Secretions

axyridis is a large coccinellid beetle with color ranging from yellow-orange to black, and the number of spots between 0 and 22. It is native to eastern Asia, but has been introduced with tremendous success to North America and Europe to control aphids and scale insects. It is commonly known in North America as Asian lady beetle, or Japanese ladybug, and in the United Kingdom as the Harlequin ladybird (the last because it occurs in numerous color forms). It is also known in North America as the multicolored Asian lady beetle, and (because it invades homes in October in preparation for hibernation) as Halloween lady beetle.

The beetles secrete droplets of hemolymph containing deterrent alkaloids through their leg joints when threatened or attacked, a behavior known as reflex bleeding. For the current study investigators at the Institute for Molecular Biology and Applied Ecology (Giessen, Germany) induced reflex bleeding in a population of 500 H. axyridis beetles and then collected and purified the harmonine content.

They reported in the September 21, 2011, online edition of the journal Biology Letters that harmonine displayed broad-spectrum antimicrobial activity that included human pathogens. Antibacterial activity was most pronounced against fast-growing mycobacteria and Mycobacterium tuberculosis, and the growth of both chloroquine-sensitive and –resistant Plasmodium falciparum malaria strains was inhibited. Harmonine displayed gametocytocidal activity, and inhibited the exflagellation of microgametocytes and zygote formation. In an Anopheles stephensi mosquito-feeding model, harmonine displayed transmission-blocking activity.

Results from this study combined with previous findings that indicated that harmonine displayed cytotoxicity against five human solid tumor cell lines suggest that this compound should be of interest to drug developers.

The broad-spectrum antimicrobial activity observed in the present study demonstrates that harmonine is an important factor in beetle immunity and may explain the invasive success of H. axyridis. What is not clearly understood is how the beetle itself resists the toxic effects of the compound.

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Institute for Molecular Biology and Applied Ecology