Coleoptera Chrysomelidae

Natural History

Distribution. The tuber flea beetle is western in distribution, although some eastward movement is evident in Canada, as it has only appeared recently in Alberta. It is highly damaging in British Columbia, where it is considered by some as be the most serious insect pest of potato, and in Washington and Oregon. Gentner (1944) found that in addition to the far western populations there was a disjunct population in Colorado and western Nebraska. Gentner speculated that this beetle might be native to eastern Colorado, and have spread to other states.

Host Plants. Tuber flea beetle feeds on a variety of solanaceous crops and weeds. The preferred host seems to be potato. Other crops that have been observed to be attacked, when potato was not available, include bean, cabbage, cucumber, lettuce, pepper, radish, spinach, swiss chard, and tomato. Several weeds, such as buffalo bur, Solanum rostratum; ground cherry, Physalis lan-ceolata; marsh elder, Iva xanthifolia; kochia, Kochia scoparia; dandelion, Taraxacum officinale; wild mustard, Brassica kaber; tansymustard, Descurainia pinnata; and lambsquarters, Chenopodium album; also are consumed by adults.

Hill (1946) conducted plant suitability experiments in Nebraska, assessing adult longevity, egg production, and larval survival on various host plants. Potato foliage was the most suitable food—egg production was highest and mortality lowest. Tomato also was a fairly suitable host, although not as favorable as potato. Buffalo bur was quite suitable for adult survival, but egg production was reduced considerably relative to potato. Plants that were decidedly less suitable included bean, ground cherry, marsh elder, and kochia. However, it is worth noting that even the less suitable hosts considerably extended longevity of adults as compared to the absence of food, and some egg production resulted from beetles fed these plants. No larval development was detected on marsh elder or kochia, but the tests were not exhaustive. Thus, though not optimal hosts, various weeds certainly would assist survival of beetles in the absence of potato and tomato.

Natural Enemies. Natural enemies seem to be rare or nonexistent (Neilson and Finlayson, 1953).

Life History and Description. There are 1-2 generations annually, though two is most common. Most of the second brood beetles enter diapause, but a few produce eggs and initiate a third generation. In some locations, only a single generation develops annually due to adverse weather. A complete generation requires about six weeks. Overwintering occurs at the adult stage within the soil or under plant debris, in or near potato fields, with adults first emerging in May or June (Vernon and Thomson, 1991).

  1. Egg deposition occurs for about a month, with an average of 90 eggs produced per female. However, Hill (1946) reported good survival for 40-60 days, with fecundity of up to 250 eggs per female. The elliptical eggs, which measure 0.5 mm long and 0.2 mm wide, are deposited singly in the soil adjacent to food plants. Eggs hatch in about 10 days.
  2. The larvae feed below-ground on the roots of plants. The larva is elongate in form, and bears three pairs of true legs. It is white, though its head capsule is brown. It measures only about 1 mm at hatching, but grows to about 5.3 mm long and 0.8 mm wide at maturity. First-generation larvae are present from early June to mid-July. Larval development requires about three weeks. Second-generation larvae are present from about mid-July to mid-August. Third-generation larvae are present from about mid-August until October.
  3. Pupation occurs in the soil. The pupa is white and measures about 2.5 mm long and 1.5 mm wide. The duration of the pupal stage is about two weeks.
  4. The adult is a small, shiny black beetle, measuring 1.5-2.0 mm long. Its antennae and legs are orange, and the elytra bear rows of fine punctures. The thorax and elytra are covered with a fine layer of hair. The hind femora are enlarged. The pre-oviposition period after adult emergence from overwintering is 5-8 days. Oviposition can occur over a period of 12-54 days, but averages about 37 days.

The biology of tuber flea beetle was given by Hill (1946), Neilson and Finlayson (1953), Beirne (1971), and Howard et al. (1994).

Insect Black Beatle Pictures

Damage

Damage by tuber flea beetles is typical of flea beetle injury. Adults eat small holes in foliage and larvae feed on the below-ground parts of plants. (See the discussion on Potato Flea Beetle for a more detailed description of Flea Beetle Damage.) Tuber flea beetle apparently has a high rate of reproduction with excellent survival or both, because low spring populations often result in considerable damage by autumn (Vernon et al., 1990). Second-generation larvae are particularly damaging, because they feed on the surface of potato tubers, in the same manner as potato flea beetle, reducing their commercial value. Growers attempt to maintain a first-generation beetle density of less than 0.05 beetles per meter of row (or 1 beetle per 10 sweeps), a density that produces minimal damage to tubers by the second generation (Vernon and Thomson, 1993). Damage is often greatest along the edges of fields. Tuber flea beetle is considered much more damaging to potato tubers than to potato flea beetle.

As is the case with many flea beetle species, activity and damage are higher under hot and dry conditions. Overwintering survival is poor under exceptionally cold conditions, reducing damage during the subsequent summer. Organic soils are more favorable for flea beetle population growth than to mineral soil (Vernon and MacKenzie, 1991a).

Management

  1. Tuber flea beetles prefer to feed and mate on the upper surface of foliage, and are easily monitored visually. This is the only practical method for newly emerged or small potato plants, as other methods are too destructive. As plants mature, other techniques, such as use of a sweep net, are more appropriate (Vernon et al., 1990). Flea beetle densities tend to be higher along the margins of potato fields (Cusson et al., 1990), suggesting that although overwintering may occur within a field, most beetles may overwinter in weedy or untilled areas. This aggregated distribution must be considered when deciding on the need for control.
  2. Potato growers in British Columbia apply insecticides from plant emergence to maturity to prevent damage by these flea beetles (Vernon and MacKenzie, 1991a). Systemic and nonsystemic granular insecticides are commonly applied to prevent damage. Foliar insecticides also are effective, but it may be necessary to apply insecticides every week (Vernon and MacKenzie, 1991b). If the overwintering population can be reduced adequately, the need for late season pest suppression is reduced. Insecticide resistance has been a problem in British Columbia (Finlayson et al., 1972), but now many insecticides are effective.

Cultural Practices. Flea beetle densities are higher in potato fields where potatoes have been grown previously (Cusson et al., 1990), suggesting that there is considerable value in rotating crops. If potatoes are to be grown for the first time in a field, there is little likelihood that flea beetles are present; thus, treatment of the edge rows with a granular systemic insecticide should provide a chemical "barrier," protecting the remainder of the crop from invading beetles. Early harvesting of potatoes can help avoid most of the damage caused by the summer generation of larvae.

In some areas potatoes can be planted either early or late in the growing season. In such locations, beetles typically attain moderate densities in the early season plantings and then disperse to later plantings, where significant damage occurs. It may be advisable to treat early season plantings to avoid damage in adjacent late season plantings if the early plantings are smaller in acreage. In any event, growers should be aware of the inoculum potential of early crops.

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