Does Freezing Kill Hollyhock Weevil Larvae?

The Culprits

• If your once-dense stand of towering hollyhocks has thinned gradually in recent years, suspect hollyhock weevils (Apion longirostre). Seen under a magnifying glass, these 1/8- to 1/4-inch, dark-gray pests resemble tiny elephants with upraised trunks, or snouts. The weevils' jaws are located on the ends of these snouts, and the insects use them to chew on your hollyhocks’ new spring leaves and flower buds. This largely nocturnal feasting results in a peppering of holes on the unfurling leaves and petals, but it's far from the worst of what these pests do.

Reproduction

• During their extended between-meal breaks, hollyhock weevils spend their time mating. Male hollyhock weevils are protective spirits, and rarely leave their mates alone in case a competitor is lurking nearby. After mating, the females migrate to your hollyhock’s developing flowers, chewing deep holes with their extra long snouts and depositing an egg in each hole.

Damage

• Newly hatched larvae burrow into the flower’s embryonic seeds and consume them from the inside. They pupate inside the seedpods and crawl out as adults to drop to the soil for overwintering or, if it's late in the growing season, overwinter as pupae in the seedpods. On the outside, your hollyhock blooms and seedpods look quite normal. The chances of their producing enough viable seed to replenish your aging plants, however, have been decimated.

Cultural Control Methods

• To eliminate hollyhock weevils without resorting to insecticides, begin checking your plants for the adult pests in early spring. The mating insects are fairly easy to spot on the leaves. Have a pail of soapy water handy, and place a cloth on the ground beneath the plant you’re monitoring. Shake the hollyhock to dislodge the weevils onto the cloth and drown them in the water. As soon as the infested hollyhocks’ blooms fade, remove their larvae-hosting seed pods. It may be too late for those plants to produce viable seeds, but you’ll be protecting future plantings from infestation. Frequently clearing debris from the hollyhock bed also removes concealed adult weevils.

Insecticide

• Treating your infested hollyhocks with malathion insecticide kills the adult weevils without doing anything to rid you of their seedpod-protected larvae. If you want to proceed, mix a spray containing 1 tablespoon -- or the label’s specified amount -- of malathion concentrate in 1 gallon of water. To avoid harming honeybees or other beneficial insects, treat the plants in the evening. Wearing protective clothing and eyewear, saturate the stems, leaves and flowers. Don’t allow children or pets near the plants until they dry, and wash your clothing right after spraying the plants.