STAR-K Guide to Checking Lettuce for Insects

There are three main species found on lettuce and other leafy vegetables. Aphids, thris, and flies. Aphids are small round green bugs. Very difficult to see with the naked eye, their color and size allows them to become virtually invisible on the host leaf. Most aphids measure about 1 millimeter in length, about the size of the letters on a nickel. To properly check for aphids, it is advisable to use a light box. The thicker insect remains dark while light passes through the leaf. Thris are small elongated brown insects. Roughly the same length as an aphid, these pests are only half the width. Easily mistaken for a piece of dirt, it takes some practice to recognize what is an insect and what is not. In the beginning, many find it helpful to have a magnifying glass or jeweler's loop on hand to confirm the actual identity of the speck. Thris move very quickly and may run under curls in the leaf when exposed to light. Vegetable flies resemble house flies. About twice the size of aphids and thris, this black winged insect is the easiest to find.