Q. I planted a sweetbay magnolia last spring, and it has grown well with no problems until this spring. I noticed that most of the leaves are riddled with small holes. I have looked and looked for insects but I cannot find anything. Do you have any idea what is causing this or what I can do to stop it?
A. Yellow poplar weevil (Odontopus calceatus) is probably the culprit. Adult feeding creates numerous small holes that dot the leaf. Sometimes the damage is done while the leaf is still rolled up in the bud, so the resulting holes sometimes form a pattern.
Weevils are just beetles with an elongated snout. Yellow poplar weevil adults are black-brown and about 3/16-inch long. They overwinter in the leaf litter around the base of host trees that include magnolias, tuliptree (Liriodendron tulipifera) and sassafras (Sassafras albidum). They become active on warm days in early spring, when they feed on buds and newly expanding leaves.
In late April or early May, weevils lay their eggs down the midribs of leaves, on the undersides. The larvae hatch quickly and begin feeding as leafminers between the layers of the leaves. They create a blotch-shaped mine at the tip, or apex, of the leaf. Yellow poplar larvae pupate inside the leaves and hatch out as adults. The new adults feed from late June through late July and move to their overwintering sites by mid-August. They will not cause any more damage until they resume feeding the following spring.
We have cyclical outbreaks of this pest every three to five years or so. Their population is held in check most years by parasitic wasps that attack the larvae and pupae while they are inside the leaves. Even when we have outbreaks, their damage is more cosmetic than life-threatening, and rarely warrants control in the landscape.
Yellow poplar weevils generate many calls to extension offices because people find them on their clothing and mistakenly think they are ticks. Ticks do not have antennae and they cannot fly. These weevils do not bite people, nor do they transmit disease.
Send questions to Sandy Feather by e-mail at firstname.lastname@example.org or by regular mail c/o Penn State Extension, 400 N. Lexington Ave., Pittsburgh 15208.