Something Else Sunday: War of the Worlds in reverse

If you have read/seen the War of the Worlds (I admit to only having seen the 2005 version of it), you might remember that in the end, after destroying half of the world, the aliens suddenly collapse, as they got infected with Earth’s own trusted micro-organisms.

Last week, a new finding, published by Andreas Vilcinskas and his colleagues, suggests that a similar thing is happening in the insect world…except in reverse order!

One of the native ladybirds in Europe, the seven-spot ladybird (Coccinella septempunctata) is not doing very well at the moment. This is because some time ago, the Asian Harlequin ladybird (Harmonia axyridis) was introduced in Europe for pest control (they’re very good at eating aphids and other pest-insects). Unfortunately it started doing too well, and is now slowly replacing our own beloved seven-spot ladybird.

The seven-spot ladybird (Coccinella septempunctata)

The seven-spot ladybird (Coccinella septempunctata)

Ladybirds tend to eat each others larvae and eggs. It was previously found that when the seven-spot eats the eggs of the Harlequin, the seven-spot dies. However, the other way around this is not the case! How can this be?

Vilcinskas and colleagues show that the Harlequin ladybird has a lot of microsporidians (unicellular parasites) in its body. However, these parasites do not kill the Harlequin. Instead, they just carry them around in their body, and when the seven-spots eats a Harlequin egg, the parasites will infect and kill the poor seven-spot. This might explain why the seven-spot is doing so badly at the moment: it’s succumbing to the biological weaponry of the Harlequin!

So this time, not the natives, but the aliens are carrying the disease!

Source:Vilcinskas A., Stoecker K., Schmidtberg H., Röhrich C.R., Vogel H. (2013) Invasive Harlequin Ladybird Carries Biological Weapons Against Native Competitors. Science 340, 862-863

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