Mint root borer
Wings are cream colored at the base and a mixture of rust-orange and dark brownish-gray toward the wing tip. Wings are also marked with dark lines. The wingspan is approximately 0.8 in (20 mm). Males and females appear nearly identical, although the front wings of females have slightly more orange patches.
Eggs are laid along the veins on either side of leaves. They are oval, flat, and transparent to white and turn greenish-brown prior to hatching. Depending on the temperature, eggs hatch in approximately 5 to 10 days.
Larvae feed on leaves for 2 to 4 days then drop to the soil surface and burrow into a rhizome. Mature larvae are white or tan with a reddish-brown head and are about half an inch long. In October, larvae leave the rhizomes to overwinter in hibernacula just below the surface (4/5 to 1 5/8 below). Larvae pupate in spring.
Adult mint root borers start emerging between early and mid-June, with peak emergence occurring from mid to late July. Mint root borers have one generation per year.
DAMAGE: Larvae bore into and feed on rhizomes of peppermint. Economic loss is due to decreased oil yield, reduced quality of oil, and shorter productive expectancy of mint stands.