|I have a lemon tree which is the regular victim of semi-defoliation. I have inspected the plant at day and night, but I can find no bugs or worms.
|Slugs and snails can be quite sneaky so check to make sure they're not feasting on the leaves. If there are no slime trails up the trunk or on the branches of the tree, then I suspect the defoliation is caused by and environmental problem such as over-watering. Citrus like moist soil, but not standing water. Make sure that the soil drains quickly. They also benefit from some organic mulch over the roots to keep them cool. Withhold fertilizers at this point and prune lightly to encourage new growth. Then just watch carefully for scale, aphids, mealybugs or snails.