Try locating a leaf beetle on a leaf. It’s difficult, and not just because these insects are tiny, barely half the size of our smallest fingernail. They have evolved a unique strategy to blend out of sight: they resemble the feeding marks – holes or scrapes – they make on leaves. This could be to avoid being seen by predators, say scientists.
A leaf beetle systematically eats out small bits of the leaf it rests on, creating numerous holes or scrapes on it. These marks are as big and of a similar colour as the beetle itself, often making a predator mistake a dark beetle for a hole in the leaf.
This deception even fooled entomologist Alexander Konstantinov (Smithsonian Institution, U.S.A.) on his beetle collection trips. Did leaf beetles across the world – there are more than 30,000 species – exhibit this masquerading strategy too?
From field data collected over 16 years, Konstantinov and a team including scientist K. D. Prathapan from the Kerala Agricultural University in Thiruvananthapuram studied the colours and sizes of 119 leaf beetle species found worldwide (including 24 species from India), as well as the colour of the beetles’ feeding marks. They also studied photographs which had inadvertently recorded some of these beetles on plant leaves in Europe in the 1920s.
A majority of the 119 beetles were found to be masqueraders.
Their results, published in the Biological Journal of the Linnean Society, show that masquerading beetles are small (about 4 mm long) and mostly feed on leaves exposed directly to the sun. They are uniformly dark- or light-coloured and their shells lack warning colours or contrasting patterns. The team find that beetle body colour is linked to the colour of their feeding marks: beetles that make dark feeding marks are dark in colour and those that make light-coloured marks, pale.
Which came first?
That these beetles could have evolved to be dull and uniformly coloured because it makes them harder to spot is an interesting hypothesis, but the study has several gaps that need to be addressed, says scientist Deepa Agashe of National Centre for Biological Sciences, Bengaluru, who studies evolutionary and allied ecological processes and is not part of the study.
“An alternative hypothesis is that the behaviours necessary to make light or dark-coloured damage (i.e. chewing partly or fully through the leaf) evolved later,” she wrote in an e-mail to The Hindu. “It needs to be tested more rigorously.”
