Invasive Harlequin ladybird larvae use cannibalism as a survival tactic
05 Feb 2014
Scientists have shown that young harlequin ladybirds (Harmonia axyridis) show cannibalistic behaviour - eating eggs of their own species, to survive in new habitats. The findings are the first evidence that invasive species use cannibalism as a survival tactic, and are published in the open access journal BMC Evolutionary Biology.
Harlequin ladybirds are also known as Asian ladybirds, as they are native to Japan, China, Korea and Russia. After they were introduced to North America to control aphids in greenhouses, they went on to colonize much of the continent and Western Europe, as well as parts of South America and Africa, and are known as the most invasive species of ladybird. Invasive harlequins often replace other species native to these areas and can cause serious disruption to ecosystems.
Scientists from France, Belgium, Russia and the UK looked into how cannibalism fits into the invasive behavior of this species. They compared three groups of samples; invasive species from Belgium and France; native species from Russia and Japan where the bugs originate; and harlequins grown in the lab.
They found that invasive larvae from France or Belgium were much more likely to cannibalize eggs than those that developed in their native environment, or in the lab. Adults, on the other hand, showed a low rate of cannibalism in all groups.
The scientists suggest that this is because, unlike adults, larvae are unable to move from the leaf where they hatched to find other sources of food, and so cannibalism is their reaction to nutrient-poor surroundings to which they have not adapted.
The scientists also investigated whether the stage of the invasion affected the ladybirds cannibalistic behavior, by comparing samples from areas of France that had recently been invaded, to samples collected in Belgium, where the species was first sighted in 2001. They found that this made no difference to the rate of cannibalism, suggesting that the tactic was beneficial to the larvae past the initial stages of invasion.
Dr Benoit Facon from the French National Institute for Agricultural Research says: "¥In ladybirds, victims of cannibalism are usually defenceless life stages such as eggs, young larvae or quiescent pupae. Fellow ladybirds are a high-quality resource, so cannibalism gives clear nutritional benefit, particularly when resources are limited. It may also help ladybirds by getting rid of competitors for resources."
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Notes to Editor
1. Cannibalism in invasive, native and biocontrol populations of the harlequin ladybird
Tayeh A, Estoup A, Lombaert E, Guillemaud T, Kirichenko N, Lawson-Handley L, De Clercq P, Facon B.
BMC Evolutionary Biology 2014, 14:15
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2. Images available here. Please credit to Ashraf Tayeh
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