Scientists have discovered two new species of leaf beetles in southern India that display a novel way of using leaf holes and their fecal pellets to build shelters – a nesting behavior previously not known among leaf beetles.
Discovered in the forests of the Western Ghats in the states of Karnataka and Kerala, the scientists have named these pin-head sized leaf beetles Orthaltica syzygium and Orthaltica terminalia, after the plants they feed on: Syzygium species (e.g., the Java plum) and Terminalia species (e.g., the flowering murdah). Their findings were recently published in the journal Zookeys.
This image shows Orthaltica terminalia, one of the two newly discovered species. Photo by Alexander S. Konstantinov.
After several months of observing the behavior of these Orthaltica beetles in the field, the team found that the tiny adults of these species are so small they are incapable of cutting holes into the leaves. Instead they opportunistically use leaf holes previously created by larger leaf beetles that cut into the leaves while feeding.
The tiny leaf beetles, unable to cut, simply scrape the leaf surface to feed.
“These scraped areas look like trenches on close examination or under a microscope,” says Prathapan Divakaran, lead author with the Department of Entomology, Kerala Agricultural University, India.
The team also found that the beetles were not particularly picky about the holes they use. When they punched artificial holes into some leaves, the beetles readily used them as shelters. In fact, the beetles not only occupied the holes, but also resized and reshaped them by constructing walls made from their fecal pellets.
A shelter on the leaf, with feeding trenches radiating from the leaf-hole shelter. Photo by Kaniyarikkal Divakaran Prathapan.
“They partition the hole so that rest of the space can be occupied by other beetles and each of them have ‘privacy’,” explains Divakaran. “Moreover, unnecessary, inconveniently large holes need to be reshaped or resized to suit their exact requirements. So they use fecal pellets like building blocks or bricks to create the partition.”
While most holes housed single occupants, large holes were often used by more than one individual if beetle population densities were high. The team observed that the leaf beetles used these holes primarily for shelter, staying inside them as much as possible and leaving only to eat by creating feeding trenches.
“Leaf-hole shelters provide a roosting site that offers a certain degree of camouflage as well as protection,” state the authors.
Triangular-shaped artificial leaf-holes, used as shelter by the newly found beetle with feeding trenches radiating from holes. Photo by Kaniyarikkal Divakaran Prathapan.
To establish this, the scientists used their fingers and a stick to scare off the leaf beetles. On sensing this threat, the beetles immediately shifted their positions to the opposite side, making them “invisible” to the enemy. They responded similarly whenever an ant appeared next to their hole.
A highly cost-effective mechanism, the leaf-hole shelters provide a “behavioral novelty of evolutionary significance,” note the authors. Additionally they write, “The use of excreta for the construction of defensive structures or retreats was, until now, not known for adult leaf beetles.”
Citation: Prathapan KD, Konstantinov AS, Shameem KM, Balan AP (2013) First record of leaf-hole shelters used and modified by leaf beetles (Coleoptera, Chrysomelidae), with descriptions of two new Orthaltica Crotch species from southern India. ZooKeys 336: 47-59. doi:10.3897/zookeys.336.5435
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