The multicoloured Asian ladybird beetle (Harmonia axyridis (Pallas, 1773)) is a well-known species overseas and in Europe which turned out to be of a well estimated natural enemy an invasive alien species (IAS). Unfortunately, feral populations of H. axyridis invaded most European countries and some of Africa after the New World. It became a hazard for many native ladybird H beetle species as well as for other aphidophagous arthropods by competition and intraguild predation as well as a pest and human nuisance.
H. axyridis has many colour forms such as succinea, spectabilis, conspicua, autlica, nigra etc.
In some studies were indicated that melanism is known to have an impact on vigour in H. axyridis, and the flexibility of melanization may have a role in thermoregulation, chemical defence and might accelerated its spread as an IAS.
http://www.gen.cam.ac.uk/research/jiggins/pdfs/Michie2010.pdf
http://www.eje.cz/pdfarticles/103/eje_098_3_287_Soares.pdf
http://link.springer.com/content/pdf/10.1007%2Fs10905-013-9384-6.pdf
http://onlinelibrary.wiley.com/doi/10.1111/j.1420-9101.2010.02043.x/abstract
http://www.azoresbioportal.angra.uac.pt/files/publicacoes_Supplement_5_Aphidophaga.pdf#page=55
Has anybody found an obvious correlation between colour forms of H. axyridis and its invasiveness and aggressiveness?
Personally, I have been able to analyze several dozen cases of urban infestations by H. axyridis.
In all cases there were no black shapes. All specimens were orange in color.
I guess it is not a simple correlation, but there are differences shown for some groups if invasiveness is measured in terms of body size, fecundity etc.. Soares et al. 2001 showed that var. aulica is larger and has higher fecundity than var. nigra. One could study life-history traits of several var. of H. axyridis to answer your question.
Melanic forms appear to be rare in invasive populations, although they do occur. The only place I have ever seen them in North America is in the Pacific Northwest where they would be thermally advantageous.
I share opinion of Moreno Dutto. I haven't seen many of black forms - they were rather rare in my observations of this species.
Dear All,
In fact, succinea form predominates generally, but spectabilis and conspicua forms had quiete a high percentage in Belgium and England (see the presented table). Yesterday, I sampled an alfalfa field in Hungary where I found that 15% of H. axyridis adults was melanized. Certainly, n was only 20.
Melanism confers a thermal advantage in regions with lots of cool, cloudy weather and it is in such places we would expect melanic forms to reappear in invasive populations that otherwise lack them. But it is more complicated because melanism has pleiotropic effects on other traits, including fertility, that may contribute to selection against it in the absence of an environmental advantage. See here: http://link.springer.com/article/10.1007/s10905-013-9384-6
I have examined (or plainly seen) tens of thousands of 'harlequin' individuals in South Africa since 2007. Every single one belonged to any of the various subforms of the colour form succinea -- no melanics whatsoever. Published herein: https://www.researchgate.net/publication/202379480_The_establishment_and_rapid_spread_of_an_alien_invasive_lady_beetle_Harmonia_axyridis_(Coleoptera_Coccinellidae)_in_southern_Africa_20012009/file/60b7d516b36afb7d0c.pdf .
The 'harlequin' invasion of southern Africa was rapid and the range of the invaders is still expanding before our very eyes. I think that "our" Harmonia axyridis are perfectly invasive, thank you very much, but there is no other colour form to compare its invasiveness to (let alone its "aggressiveness"). I cannot think how its invasiveness in southern Africa can be compared with that in another place. Come to think of it ... how can one compare the relative invasiveness/"aggressiveness" inside and between populations? To calculate the fraction that each colour form contributes to a population seems too simplistic and ignores the beetles' genetic predelictions, geographic characteristics, atmospheric influences, possible unequal fitness for other reasons than colour form, or founder effects. Indeed it is the bridgehead effect that caused the extreme genetic homogeneity of the South African 'harlequins' (Lombaert et al. 2010: PLoS ONE 5, e9743. doi: 10.1371/journal.pone.0009743).
Article The establishment and rapid spread of an alien invasive lady...
Dear Andras,
in the database of the Hungarian Harlequin Project the validity of almost all data are supported by photographs taken by the recorders. Both groups of beetles or single specimens are photographed and I think it would be easy to correlate the number of recorded colour forms to 'invasiveness' (if it was able to define 'invasiveness' on a measurable way). Lat/long or any environmental factors are likely to play an important role in this case so these variables should be considered as well. Although this is not a direct answer to your question it may be a useful starting point.
Dear Riaan,
Thanks for your answer, and comments. Your data may be of interest also for others.
I am a humble entomologist with a one person staff (this is myself). However, I can afford thinking in a limited way but not the realizing of sophisticated investigations. Unfortunately, I was able to ask merely so too simplistic questions because I know the limits of my opportunities. Genetic predilections (?), geographic characteristics, atmospheric influences, possible unequal fitness for other reasons are really fascinating challenges for a team with suitable facilities. Certainly, the Plos One article is motivating.
Dear Gábor,
Thanks for your answer as well as for the availability of information. It is possible I misused the word “invasiveness” but when observing new species or their occurrence, the study of some simple characteristics may be of importance. One should be prepared for a possible deductive way.
Dear Andras,
There was no problem with the expression, I was just wondering how would it be possible to statistically incorporate this into an analysis.
dear Andras and others,
as far as I know, no one has been studying the difference in aggressiveness, or e.g. predation rates (including intra guild-) between color forms of Harmonia. in my view, this is a very useful topic of research, especially if it is done in combination with study of interactions with local (abiotic) conditions. to put it in terms of invasion success is less feasible (if at all) because of the complex nature of such a variable (and hence its definition). but indeed it has been shown that melanic morphs of ladybird species (e.g. 2-spot) are more active under certain climatic conditions (e.g.de jong et al. 1996, j. exp. biol.) which might influence also their relative fitness in invaded areas with such climatic conditions. this might, for example, work through level of agression. very interesting topic! it would indeed be very good to also study changes in morph frequencies, but it would be more useful to relate this to some measurable variables than to "invasion success"
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