Platyptilia carduidactyla Riley Lepidoptera Pterophoridae

Natural History

Distribution. This native insect is found widely in North America. Artichoke plume moth is damaging throughout the west, from British Columbia to southern California, and east to Montana and New Mexico. It is also known from eastern North America, but in Canada it is known only as far east as Ontario, and in the United States it occurs as far east as New York and North Carolina but is absent from most southeastern states.

Host Plants. Artichoke plume moth attacks thistles in the family Compositae. Several weedy Cirsium species are suitable hosts, and some are preferred over globe artichoke. Other weeds also known to be hosts are milk thistle, Silybum marianum; and at least on one occasion Napa thistle, Centaurea melitensis. Despite the reported preference for weed species, artichoke is regularly attacked in California, where most artichoke is cultivated. Artichoke can serve as a host during the entire year, but a sequence of weedy thistle species is usually required in non-agricultural habitats. Lange (1950) and Turner et al. (1987) provided lists of known-host plants.

Natural Enemies. Several natural enemies are known, including a variety of Hymenoptera (Braconi-dae, Ichneumonidae), Diptera (Tachinidae), lacewing (Neuroptera: Hemerobiidae), rove beetles (Coleoptera: Staphylinidae), the whirligig mite, Anystis agilis (Banks) (Acarina), as well as spiders and birds. In California, Diadegma acuta (Viereck) (Hymenoptera: Ichneumoni-dae) is the most widespread and effective parasitoid, attacking larvae in their burrows. Other parasitoids were documented by Lange (1941) and Bragg (1994). Life table analyses conducted by Goh and Lange (1980b) suggested that much of the natural mortality occured soon after egg hatch. Predation and drowning were important factors at this time; once larvae began to burrow they were much less affected by such mortality agents.

Life Cycle and Description. There are three generations annually in California, where considerable overlapping of generations occurs, and all stages of development can be found throughout the year. The number of generation in New York was reported to be one, whereas two were reported from Minnesota. Development time is quite long, requiring about 110140 days for a complete life cycle, so it seems improbable that there was more than one generation in most of the North.

  1. The oval eggs are glossy and yellow, and measure 0.52-0.66 mm long and 0.26-0.35 mm wide. They are deposited singly and externally on various plant tissues, especially the undersides of leaves, and they may be attached either on the side or on end. Females prefer to attach their eggs among leaf hairs, and avoid smooth substrates. Mean production was estimated at 170 eggs (range 70-300 eggs) by Lange (1941) but at about 250 eggs by Bari and Lange (1980). Duration of the egg stage varies with temperature, but averages 15 days (range 8-24 days) during the spring in California.
  2. Upon hatching, the larva measures about 1 mm long, and bears 4 pairs of prolegs. Larvae often feed on young foliage during the first two instars, and then burrow into the stalks or flower buds. Lacking suitable young foliage, however, they immediately begin to burrow. There are four instars. Mean duration (range) of the instars is 8 (8), 5.2 (5-6), 7.1 (5-12), and 19.4 (16-26) days, respectively. Thus, larval development times of 40-60 days are common, depending on weather. The larva is yellowish for the first three instars, and whitish during the fourth instar. During all instars the head, true legs, cervical shield, and anal plate are black. The head capsule widths are 0.24, 0.43, 0.67, and 1.06 mm for instars 1-4, respectively. Body length increases to about 12 mm at maturity, and the larva is rather stout.
  3. The pupa varies from yellow to brown, and measures about 10-12 mm long. The abdomen bears tooth-like spines that project posteriorly. Pupation does not always occur within a cocoon, but a thin silken cocoon tends to be present if the larva pupates in an exposed location such as among old senescing leaves and leaf litter. Often the naked pupa is found within the burrow of the larva. Duration of the pupa is about 24 days (range 22-28 days).
  4. The adult is a small yellowish-brown moth with a wingspan of 18-30 mm. The forewing is lobed, with a cleft extending inward about one-third the length of the wing. The forewing also bears a dark triangular mark adjacent to the cleft, and extending to the leading edge of the forewing. The hind wing is even more divided, consisting of three large lobes;

Artichoke plume moth larva.

Artichoke plume moth larva.

Artichoke plume moth pupa.

Artichoke plume moth pupa.

Adult artichoke plume moth.

the color is uniform brown. The legs are light in color except that they bear dark bands at the joints. Adults normally are not active during the day, and tend to rest on the underside of foliage, but they make short flights if disturbed. The temperature threshold for flight is about 8-10°C. Mating usually occurs within three days of emergence, and adults display a pre-ovipositional period of about 3-8 days. Adults live for up to 30 days. Females produce a sex pheromone (Klun et al., 1981) with maximal pheromone release about 4h after sunset (Haynes et al., 1983).

The most complete accounts of artichoke plume moth biology were supplied by Lange (1941, 1950). Bari and Lange (1980) provided information on developmental biology.

Damage

The larvae may feed on any portion of the plant, but they are usually found in the developing flower head, or bud, of the artichoke. Small larvae may burrow through the tissue of the outer bracts. As the larvae mature, they tunnel into the inner portions of the fruit. Larvae sometimes feed on the leaf tissue, especially the newly formed foliar tissue at the center of the plant, and sometimes burrow into the stalks and crown, including short distances below-ground. Artichoke plume moth is often considered to be a serious limiting factor in commercial artichoke production.

Management

  1. Distribution of eggs and larvae was studied by Goh and Lange (1980a). During the vegetative or prebloom stage, most eggs and young larvae were found on the young leaf tissue at the center of the plant. As blossoms are produced, however, eggs are deposited on the leaves just below the flower heads, and virtually all the larvae are found within the buds. Moths can be captured with light traps. Sex pheromone can be used to bait traps for population monitoring, but can also be used to permeate the atmosphere and disrupt mating (Haynes et al., 1981).
  2. Foliar insecticides, including Bacillus thuringiensis, are often applied to protect artichoke from artichoke plume moth. The preferred materials affect both the adult and larval stages, and this often limits use of Bacillus thuringiensis to tank mixes with chemical insecticides. Insecticide use sometimes induces outbreaks of twospotted spider mite, Tetrany-chus urticae Koch.

Cultural Practices. Sanitation is an important element in artichoke plume moth management. Infested artichokes should be shredded, deeply buried, fed to livestock, or otherwise destroyed and not discarded in the field, because moths emerge successfully from infested buds. Similarly, destruction of plants after harvest can be beneficial if they are infested. Weedy thistles should be eliminated if found growing near cultivated artichoke as these weeds can provide inoculum for crops.

Biological Control. The bacterium Bacillus thurin-giensis and the entomopathogenic nematode Steiner-nema carpocapsae have been shown to provide effective suppression of artichoke plume moth larvae. The dense vegetative growth and tunneling behavior of larvae provide suitable microhabitat for nematode survival during the prebloom period, but not during the fruiting period (Bari and Kaya, 1984). At planting time, artichoke cuttings can be soaked in a suspension of entomopathogenic nematodes to reduce the likelihood of planting insects into a field along with the new crop.

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