Like other citrus trees, lemon trees are susceptible to a wide range of pests, some insects being more prevalent than others depending on the region where you live. The most common bugs found on lemon trees include brown soft scales, citrus thrips, aphids, citrus whiteflies, citrus bud mites and citrus red mites, as well as snails and Orangedog caterpillars. Some of these lemon tree bugs are tiny and difficult to see, so try using a magnifying glass to study and properly identify them. The tiniest of the lemon tree insects are scales, thrips and mites.
Look for a brown, 1 1/2- to 2-inch-long caterpillar feeding on your lemon tree's leaves to identify the Orangedog caterpillar. This caterpillar will chew on the outer edges of all the lemon tree's leaves.
Identify brown soft scales on your lemon tree by looking for tiny, immobile bugs on the foliage and new woody growth. Brown soft scales secrete a sticky liquid substance called honeydew and feed on the tree's sap. You'll see the leaves yellowing and dropping prematurely.
Spot citrus thrips on your lemon tree by looking for curled, silvery-grayish leaves on the tree and shriveled or distorted leaf buds. Also look for lemons that are streaked with a silvery color and scabbed. Citrus thrips are miniscule in size, pale yellow or orange and found feeding on the young leaves and fruits.
Detect aphids infesting your lemon tree by looking for twisted, yellowed and deformed leaves. You'll also see honeydew, the sticky liquid substance that aphids secrete, dripping from or coating the undersides of the lemon tree's leaves.
Identify citrus whiteflies by looking for white winged insects that are about 1/12 of an inch long on the undersides of the lemon tree's leaves. Shake the branches of your lemon tree to see the citrus whiteflies take flight from the leaves. The citrus whitefly also secretes honeydew and lays its eggs on the undersides of the leaves.
Look for tiny elongated insects with four legs situated near their mouths to identify citrus bud mites. You'll likely find the citrus bud mite on the lemon tree's blooms and budding fruits during the summer.