Psylliodes punctulata Melsheimer Coleoptera Chrysomelidae

Natural History

Distribution. Hop flea beetle is found throughout northern areas of the United States and southern regions of Canada, from the Atlantic to the Pacific coasts. However, it is known as a serious pest principally in the western portion of its range—British Columbia, Washington, and Oregon.

Host Plants. This insect has a wide host range. Vegetables attacked include beet, cabbage, cauliflower, cucumber, mustard, spinach, potato, radish, rhubarb, tomato, turnip, and probably others. Other crops damaged include canola, hops, sugarbeet, and strawberry. Many weeds are known to be suitable hosts, including Canada thistle, Cirsium arvense; dock, Rumex sp.; flixweed, Descurainia sophia; pepperweed, Lepidium spp.; lambsquarters, Chenopodium album; nettle, Urtica sp.; wild buckwheat, Polygonum convolvulus; and tumbleweed, Amaranthus albus.

Natural Enemies. General predators such as birds and ground beetle (Coleoptera: Carabidae) larvae are known to feed on the adults and larvae, respectively. Wylie (1984) observed parasitism of hop flea beetles by Microctonus punctulatae Loan and Wylie and Town-esilitus psylliodis Loan (both Hymenoptera: Braconi-dae); the latter seems to attack only hop flea beetle.

Life Cycle and Description. After overwintering as adults, beetles become active early in the spring, often while snow remains on the ground. Overwintering occurs in grass and grain stubble, and in leaf litter and other debris found in woodlots. They are usually the first flea beetles found in pastures, fencerows, and roadsides among dry grasses and weeds, seeking green plants. They are fairly active fliers in the spring—a habit that seems to diminish later in the season. Although there are reports of two generations, it is now believed that only one generation occurs annually in Canada. The overwintering adults disappear in July after initiating the summer generation. Adults from the summer generation, which are destined to overwinter, begin to appear in August. Overwintering beetles do not mate until the following spring. About two months are required for a generation to be completed.

Egg. Mating commences as soon as the beetles become active in the spring, and continues until the decline of the overwintering generation, usually in July. Eggs are deposited in the soil, normally at a depth of 3.5-5.0 cm. The eggs are elliptical in shape, yellow in color, and measure about 0.30 mm long

Hop flea beetle larva.

and 0.15 mm wide. They are laid singly or in small clusters and require 2-3 weeks for hatching.

  1. Young larvae are whitish or gray, and measure about 0.5 mm long. They have a dark head and anal plate. The larvae eventually attain a length of about 5 mm, and require about 35 days to complete development of the stage. The larvae are quite active in the soil. Most are found at depths of 7.5-20.0 cm, but deeper depths are attained by some. They feed on the rootlets of crops and weeds.
  2. The larvae pupate in the soil and reportedly do not prepare a pupal cell. However, the larva shortens and thickens, remaining immobile for about two weeks before pupation. The pupa greatly resembles the adult beetle in form. Initially it is white, but gradually darkens over the two-week period the insect remains in this stage.
  3. Upon emergence from the soil, the beetle is blue-black, but soon acquires a shining bronze-black appearance. It measures 1.5-2.5 mm long, with the males consistently smaller than females. The elytra are well marked with rows of punctures. The antennae are brown and lighter in color basally. The legs are reddish yellow except for the femora, which are darker. The hind femora are enlarged. Hop flea beetle
Phyllotreta Spp Psylliodes Spp
Adult hop flea beetle.

can be distinguished from the other common pest flea beetle species by the antennae. A characteristic of the genus Psylliodes is 10 antennal segments, whereas Chaetocnema, Disonycha, Epitrix, Phyllotreta, and Systena have 11 segments.

A fairly complete account of the biology was provided by Parker (1910). Useful observations were provided by Burgess (1977) and Wylie (1979).

Damage

The adults are the damaging stage of this insect. Adults inflict typical flea beetle injury, making irregular round feeding sites in which they eat all except one layer of leaf epidermis—in this case the lower surface. The lower epidermis at the site of feeding eventually dies, however, leaving a small round hole where the beetle fed. At high densities, beetles riddle the leaves with tiny holes, effectively eating all except the veins and causing severe damage to small plants. Leaf petioles are eaten occasionally. Except for hops, mature crops are not usually injured. Although larvae feed on roots, they are not reported to be severe pests of crops. Thus, weed hosts must figure prominently in the biology of these insects.

Management

Protection of seedlings is accomplished with systemic insecticides applied at planting or foliar insecticides applied early in plant development. Row covers would protect young plants from dispersing beetles. Parker (1910) observed that later in the season the beetles were reluctant to fly or to leap. Therefore, large plants such as hop vines could be protected by placing a barrier of adhesive around the base of the plant to entangle crawling beetles.

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