Euborellia annulipes Lucas Dermaptera Carcinophoridae

Natural History

Distribution. First found in the United States in 1884, ringlegged earwig now is widespread in southern states. It is also known from many northern states, and the southernmost portions of British Columbia, Ontario and Quebec in Canada. Redlegged earwig occurs in Hawaii and has been transported to most other areas of the world, including both tropical and temperate climates. It likely is of European origin.

Host Plants. Ringlegged earwig is omnivorous in its feeding habits, taking both plant and animal material readily. It occurs as a minor nuisance in southern vegetable gardens and in greenhouses, where it nibbles on succulent plants such as lettuce. It is also documented to feed on roots or tubers of radish, potato, and sweet potato, and the pods of peanuts, though this is infrequent and normally of a little consequence. Ring-legged earwig is a voracious predator of insects and sowbugs. This predatory behavior probably offsets the small amount of damage done to plants. It also is highly cannibalistic.

Natural Enemies. The natural enemies of ring-legged earwig seem to be undocumented, though they are likely about the same as those attacking European earwig, Forficula auricularia Linneaus. Cannibalism of eggs and nymphs by adults is an important mortality factor.

Life Cycle and Description. This insect seems not to have been studied under field conditions. Three generations were observed under greenhouse conditions in Ohio—one each in the spring, autumn, and winter months. A complete generation can be completed in 61 days (Klostermeyer, 1942). Thus, under field conditions, it seems probable that at least two generations occur, one each in spring and autumn, at least in warm climates. In Illinois, adults can be found throughout the year except during winter when adults seek shelter deep in the soil. (The ringlegged earwig adult in color figure 178 is referred to on page 196.)

  1. The eggs are nearly spherical when first deposited, and measure about 0.75 mm in diameter. As the embryo develops, however, the egg becomes more elliptical, and attains a length of about 1.25 mm. The egg is creamy white initially, becoming brown as the embryo develops. Females deposit 1-7 clutches of eggs with a mean clutch size of about 50 eggs. Total fecundity is estimated at 100-200 eggs. Duration of the egg stage is 6-17 days.
  2. The nymphs greatly resemble the adult in form, differing primarily in size. Wing pads are absent. The head and abdomen are dark-brown. The pronotum is considerably lighter in color, usually grayish or yellowish-brown. The legs are whitish, with a dark ring around the femur. The cerci are moderately long, and not strongly curved. Normally, five instars are found, but six are observed occasionally. Instars are difficult to distinguish and no single character is completely diagnostic. The number of antennal segments is most useful, though this is mostly effective among the early instars. The number of antennal segments is about 8, 11, 13, 14-15, 15-16, and 14-17 in instars 1-6. Head capsule width is 0.62-0.75, 0.700.91, 0.83-1.09,1.04-1.56,1.22-1.56, and 1.40-1.72 mm for instars 1-6, respectively. Body length is 3.0-4.7, 3.9-6.9, 5.7-7.7, 6.7-10.8, 8.7-13.2, and 9.8-12.9 mm, respectively, for instars 1-6. When reared at 21-23°C, Bharadwaj (1966) reported mean development times of 11.8, 10.6, 13.4, 16.3, 20.1, and 27.0 days for instars 1-6, respectively, for a total of about 99 days. However, he observed a considerably shorter mean nym-phal development period, 83.6 days, when cultured at 20-29°C. Klostermeyer (1942) was able to rear the nymphal stage through to the adult in as little as 45 days, with an average of 81 days, when cultured at 18-29°C.
  3. The adults are dark brown, and wingless. They measure 12-16 mm long, with females averaging slightly larger than the males. The legs are pale, usually with a dark band around the middle of the femur, and often tibia, of each leg. Adults generally bear 16 anten-nal segments. The leg bands are the basis for the common name, and are readily apparent. Cerci of the adults can be used to distinguish the sexes. In the male the cerci are more curved, with the right branch of the forceps turned sharply inward at the tip. The males also possess 10 abdominal segments, whereas females possess eight segments. (See color figure 178.)

Earwigs are nocturnal. Mating occurs 1-2 days after attainment of the adult stage. Oviposition commences 10-15 days after mating, and requires about three days to complete. The adults construct a small cell in the soil in which eggs are deposited. The female drives the male from the oviposition chamber before eggs are produced. The female protects the egg clutch from mites, fungi, and intruders, cleaning and relocating them if necessary. Maternal care decreases soon after

Adult female ringlegged earwig.

nymphs hatch, disappearing after about 10 days. The female cannot tolerate the presence of her progeny once she begins production of a subsequent egg clutch. Adults are long-lived, capable of living over 200 days.

The biology of redlegged earwig was given by Klostermeyer (1942), Neiswander (1944), Bharadwaj (1966), and Langston and Powell (1975). Culture was described by Bharadwaj (1966). This earwig was included in the keys by Langston and Powell (1975) and Hoffmann (1987).

Damage

These earwigs cause little direct injury to growing vegetable crops, but can feed on both the above-ground and below-ground portions of plants. More commonly, they serve as a contaminant of produce, sometimes defecating on leafy green vegetables. They also can cause injury to stored products such as potatoes and carrots, and are important contaminants of food processing plants (Gould, 1948). These earwigs are important insect predators, and are documented to feed on such diverse prey as caterpillars, beetle larvae, and leafhoppers. Unfortunately, there seems to be no quantitative data on their relative importance.

Management

These earwigs rarely warrant suppression, but are easily killed by most residual insecticides. They also take bait formulations consisting of wheat bran, molasses, and toxicant, as well as many other baits (Neiswander, 1944). For additional information on earwig damage and management, see the section on European earwig, Forfícula auricularia Linnaeus.

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