Some of the most common species of weevils in the United States include the pales weevil, bluegrass weevil, and black vine weevil, or Otiorhynchus sulcatus. Weevils remain relatively destructive pests, especially to the outdoor activities reliant on the use of grass, such as golf courses and tennis courts. Similar to beetles, weevils are distinguished by the extended beaks that house mandibulated mouthparts used for chewing. Weevils do not bite or pierce humans looking for a blood meal, as the long snout might imply.
Appearance & Identification
What do weevils look like?
Weevils may be differentiated from other beetles by the easily recognizable elongated beak or snout and elbowed antennae. The pales weevil, Hylobius pales, typically grows to around 3/8 of an inch long and is dark, reddish-brown in color with pale yellow spots or hairs on the wing covers and thorax. The black vine weevil appears dark gray to black, may reach lengths of a little less than half an inch, and is completely flightless. The bluegrass weevil may grow up to 1/8 of an inch long and appears black in color with fine yellow hairs and scattered light gray spots on the thorax. Newly emerged adults may look a shade of orange in color until full pigmentation occurs.
Weevils may cause damage to various plants, grasses, and trees with a diverse feeding habit that varies by species. Species like the bluegrass weevil infest both golf courses and tennis courts, causing enough damage to call for a series of insecticides to be used annually in order to keep damage to a minimum. Different species of weevils may be found in crops, fields, lumber yards, greenhouses, and in varying grasslands. Certain species are nocturnal feeders, and most damage may not be found until after certain plants are moved, for instance to replant, or are sold.
What do weevils eat?
The bluegrass weevil (Listronotus maculicolis) feeds by cutting notches or holes in either the blades of grass or in the stems near the base leaving a jagged appearance or a thinning of the turf itself. Conversely, pales weevils find sustenance in logging areas containing freshly cut tops and stumps of conifers, feeding on the inner bark areas until the trees dry out. The insects may also feed on the twigs of saplings and even the stems of very young trees. The black vine weevil typically feeds at night, foraging on broadleaved vegetation and leaving marginal notches in the plants. Larvae feed on the root systems of plants, eventually moving up the roots to the stem.
The pales weevil deposits one to three eggs in the subterranean parts of stumps, roots, or the undersides of logs. Pearl-white in appearance, the egg is less than 1/20 of an inch long. Once hatched, the larva bores into the wood, making an irregular tunnel that ends in a pupation chamber. After passing through at least five larval stages, the insect goes through a pupal stage and then emerges as an adult. The pales weevil life cycle is completed in a year, but due to the cooler spring and fall temperatures the pales weevil may overwinter and emerge again the next spring.
The annual bluegrass weevil completes a full life cycle with up to two generations a year. Eggs are small and oblong and are typically found in the sheath of blades of grass, in groups of two or three. Each female may produce up to a dozen offspring, with full maturation from larva to pupa to adult taking up to two months. Again, due to harsher temperatures in the area, the annual bluegrass weevil may also overwinter and emerge the following spring to feed on turf.
The black vine weevil lays up to 500 eggs in a period of up to 21 days. Larvae hatch after about two weeks to feed on the roots of the host plant. Once temperatures drop, the larvae burrow deeper into the soil to overwinter. In the early spring of the following year, black wine weevil larvae form pupal cells, then emerge into adults, typically before the end of spring.
Problems Caused by Weevils
Weevils do the most damage to plants while in the larval stage, when the young insects must continually feed to reach adulthood. Adult weevils do marginal damage to the health of plants (the food source), though the damage itself may appear quite extensive. Golf courses, residential and commercial lawns, and even tennis courts may need repeated insecticidal treatments in order to maintain green, usable grass. For weevils that attack trees and lumberyards, trees and saplings face early destruction as the insects lay eggs and hatch larvae inside the roots and bark of young seedlings. For pine tree farms (used at Christmastime), many trees will have dead branches and needle loss caused previously by weevils.
Signs of Infestation
For weevils that infest grassy areas, destruction to turf appears as yellow or brown spots. If the infestation remains moderate, small and irregular patches of dead turf may appear. Most obvious damage occurs in late May and early June (as the larvae begin to pupate). Pales weevils attacking young trees and saplings may leave a white crystallized resin over the wounds where larvae feed, giving the seedling a sugary appearance. If numerous weevils feed on the same food source, seedlings will be completely stripped, only leaving a bare, curled stem surrounded at the base by a pile of separated needles.