Armed and Invasive! – the Asian ladybird

Armed and Invasive! – the Asian ladybird

In an effort to control aphids and other pests, the multi-coloured Asian ladybird (H.axyridis) was introduced into many other regions of the world. The name multi-coloured Asian ladybird stems from the very diverse colours this species can have (see figure below). It was introduced in North America as early as 1916. In 1988 the first established population was documented in America. Currently it can be found across North America, Europe and even in South America. So this species is highly invasive. Although this ladybird is good at limiting aphid numbers (which was the intentional goal of the releases), more and more adverse effects are being found. One of which is the negative effect it has on native ladybird species, which rapidly decline in numbers when outcompeted by the Asian ladybird. But why is this Asian ladybird so good at outcompeting native ladybirds?

Harmonia_axyridis01

©entomart


A very potent immune system

One of the factors which can explain the high invasiveness of this Asian ladybird is that it has an amazingly potent immune system. The number of genes involved in the recognition and signal transduction (see Immunity in insects) are about equal to another beetle, the red flour beetle (T.castaneum). But contrary to the number of genes involved in the recognition and signal transduction, the number of genes responding to infection is incredibly high! Where the red flour beetle has approximately 16 AMPs, the Asian ladybird has 50! This large number of antimicrobial peptides is likely helping this invasive species to survive even when infected by unfamiliar pathogens. A subset of the AMP groups is outlined in the table below with the known functions of each group. The entire story has been published open access in the Proceedings of the Royal Society B and can be found here.

AMP class

Number in T.castaneum

Number in H.axyridis

Function

Attacins

3

10

Interference of cell membrane formation

Coleoptericins

2

15

Interference with cell division

Defensins

4

19

Antibacterial

Thaumatins

4

4

Antifungal

Biological warfare

Just surviving in lots of different places due to a highly potent immune response still does not explain why it outcompetes native ladybirds. The Asian ladybirds prey on the eggs and larvae of native ladybirds, but native ladybirds also prey on the eggs and larvae of the Asian ladybird. So what makes the Asian ladybird so much more successful? A recent article in Science reports that the Asian ladybird is armed with a biological weapon. This biological weapon is a fungus, which doesn’t harm the Asian ladybird (which might be due to its immense immune system). This fungus is carried around in the hemolymph and passed on to their eggs and larvae. When native ladybirds eat the eggs of larvae of the Asian ladybird they too get infected by this fungus. Unfortunately, the native ladybirds cannot cope with the infection like the Asian ladybird can, so they die.
So when the Asian ladybird preys on the native ladybirds eggs and larvae it is fine, but when the native ladybirds try to play the same game they lose and die. In this way the stakes are against the native species and the Asian ladybirds will keep gaining terrain at the costs of the native species.

So what will happen now? Probably the Asian ladybird will keep moving into new territories and replacing the native species. Hopefully the native species will find ways to cope with this new competitor. But only time (and more research) will tell.

Sources:

Vilcinskas, A., K. Mukherjee and H. Vogel (2013). “Expansion of the antimicrobial peptide repertoire in the invasive ladybird Harmonia axyridis.” Proc Biol Sci 280(1750): 20122113.

Vilcinskas, A., K. Stoecker, H. Schmidtberg, C. R. Röhrich and H. Vogel (2013). “Invasive Harlequin Ladybird Carries Biological Weapons Against Native Competitors.” Science 340(6134): 862-863.