Depressaria pastinacella Duponchel Lepidoptera Oecophoridae

Natural History

Distribution. Parsnip webworm was originally known from Europe, and apparently was introduced to North America some time before 1869. Its distribution now includes southern Canada from Nova Scotia to British Columbia, and the northern United States south to Maryland and Arizona.

Host Plants. In addition to feeding on parsnip, this insect feeds on several umbelliferous weeds, including cow parsnip, Heracleum lanatum; and angelica, Angelica spp. Records of wild carrot, Daucus carota, are doubtful.

Natural Enemies. Parasitism varied from 0-100% in Iowa (Gorder and Mertens 1984), but was limited to the larval stage. Apanteles depressariae Muesebeck (Hymenoptera: Braconidae) is the principal parasitoid, though others have been collected on occasion.

Life Cycle and Description. There seems to be only a single generation per year, though in Iowa a few eggs are deposited in late summer, suggesting the possibility of a partial second generation. Egg to adult development times are reported to be 38 days in Iowa and 62 days in Nova Scotia.

  1. The eggs are deposited principally on foliage, and to a lesser exlent on flower stalks. They are elliptical, but slightly rectangular. They are white, and ribbed longitudinally. Egg length averages about 0.56 mm (range 0.36-1.14 mm). Duration of the egg stage is about four days.
  2. Upon hatching the young larvae bore into the blossom to feed. They prefer unexpanded flowers, and generally distribute themselves so that there is only one insect per flower head (Thompson and Price, 1977). The larval color is generally greenish-yellow dorsally with yellow laterally and ventrally, but sometimes tends toward blue-gray. The head is black, and the length of the body is well-marked with rows of raised black spots. There are six larval instars. Head capsule widths are about 0.1, 0.3, 0.5, 0.7, 1.0, and 1.6 mm, respectively for instars 1-6. Larval development requires about 21 days, with duration of the instars about three, two, three, four, three, and eight

Parsnip webworm larva.

Parsnip webworm larva.

days, respectively. The larva, at maturity, attains a length of 16-18 mm. Larvae rest within the flower or other sheltered locations on the plant, surrounded by a tunnel webbed from silk. When disturbed, the larvae retreat within the tunnel, and if pursued wriggle violently and drop to the soil. Larvae feed preferentially on plants low in furanocoumarins, chemicals that function as toxicants or deterrents for many insects (Zangerl and Berenbaum, 1993).

  1. Pupation occurs within a silken sheath, generally within the stalk of the food plant. The pupa is brown. Duration of the pupal stage is about 13 days.
  2. The adults fly at night, but are not attracted to lights. The moths are fairly large for this group of moths, with wing lengths of 9.5-13.0 mm. The front wings are yellowish-brown, marked with gray, whereas the hind wings are grayish. Overwintering occurs in the adult stage, with the adults in reproductive diapause. Egg production under laboratory conditions averages 470 eggs per female (range 170-830 eggs). Females deposit more eggs on larger plants (Zangerl and Berenbaum, 1992).

The most complete account of parsnip webworm biology was given by Gorder and Mertins (1984). Methods for rearing were developed by Nitao and Berenbaum (1988), who also provided data on developmental biology. Brittain and Gooderham (1916) gave a good morphological description of this insect, except that some of the measurements are incorrect.

Damage

Parsnip webworm feeds primarily on the flowers and seeds of parsnip, and is of concern only where

Adult parsnip webworm.

seed production is desired. The larvae web together the flower heads and feed within, leaving the flower structure a mass of webbing and feces.

Management

This insect should rarely warrant control efforts, but foliar insecticides applied before opening of blossoms can prevent larval feeding.

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