This fly’s larvae tunnel inside bitter-tasting greens like arugula and kale, leaving squiggly marks behind. The plants fight back with toxic chemicals. So before laying her eggs, the fly mom digs into a leaf and slurps its sap - a taste test to find the least toxic spot for her offspring.
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As they feed inside a leaf’s spongy layer, leaf miners etch intricate patterns that are visible to us on the leaf’s surface. The whitish tan or light gray markings can be neatly serpentine or converge and have a blotch-like appearance, depending on what insect made them. Many different flies, butterflies and moths lay eggs on the leaves of citrus, vegetables and ornamental plants that grow into leaf miner larvae.
One leaf miner that gardeners might find in their arugula is the larva of a fly called Scaptomyza. The fly is related to - and looks a lot like - the fruit fly you might find buzzing around your ripe bananas.
The chemicals called isothiocyanates that give leafy greens like arugula their bitter taste are precisely the plants’ defense mechanism against pests. Scaptomyza flies have evolved to tolerate low levels of these compounds. One way in which the flies deal with these toxic chemicals is by laying their eggs on the leaves with the lowest concentrations.
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--- Can leaf miners kill plants?
Leaf miners rarely do enough damage to even come close to killing a plant, but they make individual leaves inedible. If given enough time, a leaf miner can be particularly damaging to vegetables that are harvested specifically for their leaves. But don’t worry if you mistakenly eat a larva - it won’t make you sick.
--- How do you treat leaf miners?
Most backyard gardeners only need to remove the damaged leaves by hand. Since leaf miners are tucked inside the leaf, insecticides aren’t very effective and can hurt beneficial pest predators like wasps, spiders and ladybugs.
Gardeners with a greenhouse or large numbers of plants can use parasitic wasps to control leaf miners.
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