Thursday, February 26, 2015

Tracing Leaf Miners

A major challenge in network ecology is to describe the full-range of species interactions in a community to create highly-resolved food-webs. We developed a molecular approach based on DNA full barcoding and mini-barcoding to describe difficult to observe plant – leaf miner – parasitoid interactions, consisting of animals commonly regarded as agricultural pests and their natural enemies.

Leaf miners are plant feeding insects, mainly consisting of flies, moths, and beetles. Many of them are agricultural pests and are therefore considered economically important organisms. They feed on a wide range of plants, which unfortunately also includes cultivated plants and crops. Females lay their eggs either on the leaf surface or in a hole they punctured into the leaf. The hatched larvae will start feeding on leaf tissue making a tunnel which is called 'mine'. 

The problem is that despite their potential impact on a range of commercially important crops, we know only little about leaf miners and their interactions with other species. They are poorly studied organisms, partly due to their cryptic life-cycle which can create major challenges when attempting to incorporate leaf mining insects into complex ecological networks.

A new study is now presenting a novel way to construct precise plant - leaf miner - parasitoid interactions. Morphological identification is very difficult in all the groups and usually requires rearing of collected larvae. However, laboratory rearing is very difficult because collecting infested leaves and rearing adults from larvae within the mines often results in premature death, or one finds the mines empty as the larvae already hatched or moved on to form a new one. In order to overcome these problems the authors of the new study developed a new molecular approach based on DNA Barcoding of remnant DNA within the mines, and it worked quite nicely:

... we show how a molecular approach can be used to determine difficult and cryptic species interactions, even when an adult insect has left its leaf mine. Our molecular approach found more species and interactions than traditional approaches based on insect rearing methods, altering network structure as well as identifying previously unknown species interactions. Thus networks constructed using these molecular methods are better resolved and more useful for network ecologists.

It is very difficult to effectively control for leaf miners. Infected leaves are usually removed and discarded and pruning is often required in the event of a heavy infestation. Many species of leaf miners overwinter in fallen leaves and soil beneath the host plant. Doing a fall clean up can be beneficial in reducing these overwintering sites. In general leaf miner control relies on the use of a combination of cultural practices, including the collection and disposal of infected leaves, as well as the removal of weeds that can act as alternate hosts. That in turn requires extensive knowledge about the species-species interactions. Far more than we know at this point. This new study might help to speed up this process and gain knowledge that eventually will turn into some useful strategies.

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