Different wing colors in a harlequin ladybird specimen (4K)
The ladybeetle Harmonia axyridis is naturally distributed over eastern Asia, but was imported to the United States already at the beginning of the 20th century as pest control. At first, there was no population development in the open fields. These were at first reported from Louisiana in 1988. In 2001 the first free living specimens were for Europe discovered in Belgium. Since then the beetle distributed over several european countries, such as France, entire Germany or Switzerland.
The beetle is well known for its great form variations. Worldwide more than 200 different color pattern forms of thorax and elytrae are described. They are distinctly shaped and maintain in this shape and arrangement of pattern. But four forms dominate within natural populations. Speaking about the elytrae (not the thorax patterns), the reddish form with dark spots, as visible in my film, is one of them.
These distinct different forms must be named a polymorphism and are based on genetic information as well as on environmental conditions, such as temperature, humidity and light intensitivity. In such cases even the term polyphenism might be adequate.
According to the work of M. Gautier et al. (the genomic basis of color pattern polymorphism in the harlequin ladybird, Current biology, 28, 20), the transcription factor pannier is responsable for the genetical ly based control of this polymorphism. They discovered that different pannier alleles determine the color pattern in the different known forms. The authors furthermore report that pannier was never found before to play a keyfactor role in the pigmentation of insects.
The specimen in my footage was discovered on an urban meadow in the park area "Nordhafen" in Berlin. It's a meadow in autumn predominantly c onsisting of lucerne and clover, sorrel and yellow field cress. Different ladybeetle species could be in greater numbers found there between September and October 2019. The sevenspot-ladybird, the adonis ladybird (Hippodamia variegata)and most abundant the harlquin ladybird in all its developmental stages.
The most conspicuous character of "my" harlequin ladybird specimen was its distinct asymmetrically colored wings (elytrae). One side reddish with black spots, the other side brownish with black spots. During my research about such asymmetries in ladybirds, I didn't find recent studies, which distinctly focussed on that topic. H. E. Roy et al. reported in their book "ladybirds" (original version 1989, revised version 2013) about the existance of such differently colored wings in the same specimen. They emphasized that the phenominon was not studied in detail, but assumed different factors being eventually responsible for such a development of a beetle individual: 1) disruption of pigment production,2) mitotic mutation in early development, 3) environmental conditions, eventually influencing the colors of an originally normal developed young adult (exposed for longer time to different light intensities etc.). The latter might in the case of "my" specimen being an indeed possible factor, as it is clearly visible that also the brownish wing has at its edges some of the reddish pigments.
The beetles was filmed under artificial conditions in a soil and grass-set in my video lab. There, mites of the Gamasina (Parasitiformes, evtl. mostly Laelapidae) were common. They interstingly showed a phoretic behavior by quickly climbing onto the wings of that ladybeetle. They obviously recognized it as a suitable carrier to new habitats. I assume ladybeetles in the field not being of much attraction for phoretic dispersal, based on their life-cycles and preferred habitats.
Berlin, September/ October 2019, Copyrights Stefan F. Wirth
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