Unique food source utilisation – Issue #87

Hello Explorer,
Herbivorous insects are a farmer’s arch nemesis, due to their plant eating habits. The ways in which insects consume the plants varies greatly, some will consume whole parts of the plant by chewing it off, and others will only drink the plant sap, but all of them are a problem.
One of these herbivorous insects is a collection of species from different groups that stay inside a leaf, the Leaf Miners. The collection includes moths, flies, sawflies (wasp species), and some beetles. Leaf miners do not change the leaf morphology at all, they utilize the leaf as it is.
A leaf miner’s life cycle are as follows: The female will lay an egg either on or inside the leaf. The larva will then make its way into the leaf if the egg was laid on the leaf, and from there the lifecycle of the two different egg laying positions are the same. The larva will travel between the top and bottom epithelial (outside) cells of the leaf, consuming certain cells between the top and the bottom of the leaf. As the larva consumes the inner tissue of the leaf it leaves a clear trail in the leaf. This “tunnel” the leaf miners leave behind is often filled with frass (insect poop), giving it a distinct dark or black appearance. Once the larva has consumed its fill it will pupate inside the leaf, and once it emerges from the pupae it will chew its way out of the leaf and the life cycle will begin all over again.
Thought leaf miners are often only thought to eat plant leaves, there are some species that will mine in flower petals and the surface layers of fruit. These miners consume plants in this way for a few reasons. Firstly, the outer surfaces of the leaf that covers them offers protection, and not just protection against predators, but also against desiccation, sunburn, and protection from accidently being bumped off your food source. Secondly, they consume the most nutrient rich parts of the leaf only and do not have to digest the outer cells of the leaf, which is generally not as nutritious.
The plant species, plant part (leaf, flower petal, or fruit surface) consumed, tunnelling pattern and types of cells that are consumed, is often diagnostic of who has enjoyed the plant, even to species level. This means that each species of leaf miner has a specific pattern of feeding it follows inside a leaf, an instinctive pattern of feeding that is set within the larval DNA.
The damage a leaf miner makes might seem small, but when their population number and density increase, they can kill a plant. They kill a plant by reducing the effective photosynthesis area to below the plants survival threshold, meaning the plant cannot produce enough food through photosynthesis to survive.
Although many species of leaf miners have been declared pests, most of them create beautiful mosaics of mines on leaves in nature that doesn’t bother anyone. So next time you see a leaf with a strange pattern that seems carved on the inside of the leaf, take a moment to admire the work of the leaf miner and its instinctive feeding patterns!
Have you ever come across a leaf miner’s tunnels? Have you ever thought about the complexity and implications of instinct?

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