Epitrix tuberis
(tuber flea beetle)

E. tuberis is native to northern Colorado, USA. Gentner (1944) gives an account of its initial spread to Nebraska, Oregon and Washington. It has since spread to California, New Mexico, South Dakota and Wyoming (USA), and to British Columbia and Alberta (Canada), during the latter half of the twentieth Century. The species is still spreading.

A record of E. tuberis in Manitoba, Canada (Campbell et al., 1989; Bousquet, 1991) published in previous versions of the Compendium was included in error; neither of these publications mention the presence of E. tuberis in Manitoba.

See also CABI/EPPO (1998, No. 68).

E. tuberis is categorized as an A1 quarantine pest by the European and Mediterranean Plant Protection Organization, Russia, South Africa and East Africa (EPPO, 2003). However, E. tuberis has never been detected in potato consignments, either nationally or internationally. Nevertheless, international spread could occur if adults were carried on rooted host plants or with eggs or pupae in any accompanying soil. The spread and establishment of E. tuberis into the Old World would lead to a generalized increase in the use of insecticides on potato, rather than the occasional targeted use against existing pests.

E. tuberis is primarily associated with Solanaceae, with adults feeding on foliage and the larvae feeding on underground roots or tubers. Potato is the most significant host. Damage to other solanaceous crop hosts such as aubergine, Chinese lantern, ground cherry (Physalis spp.), tomato and tobacco (Hatch, 1971) is generally less important because adults feed on these only if potatoes are not available. In the spring and autumn, when no solanaceous crops may be available, adults may attack beans, cabbages, chard or cucumbers and various weeds.

The date at which E. tuberis adults become active and emerge from overwintering sites in the soil varies depending on location but can range from late March or early April in southern locations to early May or July in eastern Washington state (Webster, 1945). Winter survival of adults depends on the depth and quality of the soil. E. tuberis survives well in soils of 20-30 cm (Davis and Landis, 1947) but can overwinter at depths of down to 60 cm (Campbell et al., 1989). It had been thought that adults overwintered exclusively at the margins of fields previously used to grow potatoes (Cusson et al., 1990) although it is now known that a proportion of the population can spend the winter in the middle of potato fields (Vernon and Thomson, 1991). Thus, E. tuberis may be more widely dispersed in a field of second-year potatoes than in a field of first-year potatoes. Adults prefer to feed and mate on the upper surfaces of leaves (Vernon et al., 1990) although, when windy, the beetles will not be as active on the upper surfaces (Bérubé, 2000). Adults tend to move under the leaves at night. Adults will fly considerable distances to find a host plant.

Mating takes place within 24 hours of emergence and there can be repeated copulation for up to 60 days. Vernon and Thomson (1993) measured the female: male ratio as 1: 0.94. After a pre-oviposition period of 5-6 days, eggs are laid over a period of 12-55 days, with an average of 38 days (Neilson and Finlayson, 1953). A number of authors have measured egg production in E. tuberis. Jones (1944) recorded females depositing 106 to 139 eggs over 17 to 30 days. Neilson and Finlayson (1953) recorded a wider variation in the number of eggs laid from 28 to over 200 with a mean of 87. The numbers of eggs laid varies markedly with the food plant of the adult. Females feeding on potato leaves produce the most eggs. In trials where caged adults were fed potato leaves then the diet switched to a less nutritious diet, egg production fell within 2 or 3 days, then increased when potato leaves were returned to the diet (Hill, 1946). Overwintered females will lay about 150 eggs whilst females in the summer generation will lay almost double this number (about 280 eggs). Eggs can be deposited in batches of 11-15 or can be laid singly (Campbell et al., 1989) in the soil or near the base of a host plant.

After incubation of 3-14 days, the eggs hatch and the larvae feed on roots and tubers for 2-4 weeks. The larvae can be found from late May throughout the potato-growing season, depending upon when the adults emerged. Pupation takes place in the soil, and lasts 4-10 days. The time of emergence, or the numbers of adults that emerge from different soil types, does not vary significantly according to the mineral, inorganic or organic nature of the soil in which eggs are deposited (Vernon and Thomson, 1993). Adults of the overwintered generation usually die in July (Kabaluk and Vernon, 2000) when there can be overlap with the next generation of adults that emerge between early July and early September. The second generation develops in 35-85 days, compared with 27-50 for the first. Second pupation starts at the beginning of August and may continue until the beginning of November. The F1 adults then emerge, and later enter diapause to overwinter in the soil. There are usually only two generations per year (Fulton and Banham, 1962) although, depending on the date of adult emergence in the spring or early summer, and larval food availability, there may be a complete or partial third generation in a year (Webster, 1945; Campbell et al., 1989).

In laboratory studies at 21°C, Jones (1944) calculated the average times for egg, larval, pre-pupal and pupal development to be 8.0, 15.3, 6.1 and 8.2 days, respectively.

No predators or parasites of E. tuberis are reported in British Columbia, Canada (Campbell et al., 1989). Climate is the major factor limiting the distribution and population size of flea beetles (Davidson and Lyon, 1979).

EPPO (2011) describes a diagnostic protocol for adult Epitrix cucumeris, E. similaris and E. tuberis infesting potato.

E. tuberis is most similar to E. cucumeris and E. subcrinata. A specialist is required to identify specimens to species. Seeno and Andrews (1972) provide a key to Californian species of Epitrix.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Cultural Control

Control measures should focus on controlling the first generation of E. tuberis ensuring only limited treatment is necessary later in the year. In locations where E. tuberis is known to occur, growers may adopt crop rotation to prevent the build-up of E. tuberis populations in the middle of fields (Kabaluk and Vernon, 2000). Growers should also avoid planting early potato varieties. This will cause emerging overwintered adults to have to feed on less nutritious food plants and greatly decrease the number of first-generation larvae available to infest later planted potatoes (Hill, 1946).

Economic Thresholds

To determine whether any chemical control measure should be applied, the number of adult E. tuberis should be monitored within a crop. When potato plants are less than 30 cm tall, a visual examination of plants lasting 5 to 20 seconds per plant is sufficient. Ten plants should be examined per row. The accuracy of monitoring E. tuberis using visual observations can be affected by observer experience and competence, the time spent observing each plant, the time of day, plant height and weather (Vernon et al., 1990). The greatest accuracy is achieved in the morning in calm weather. Plants over 30 cm in height should be sampled by sweep netting. Ten adjacent consecutive circular sweeps should be made enabling a sample to consist of sweeps from around 100 plants. Sweep netting is approximately 1-4% accurate (Bérubé, 2000).

There have been various thresholds suggested when action to control E. tuberis populations is warranted. Cusson et al. (1990) describe a practical action threshold of one beetle per 10 plants. Alternatively treatment may be necessary when a population averages three or four adults per 10 m row of potatoes (Berry, 1998). Bérubé (2000) suggests a threshold of one beetle per 100 plants.

Chemical Control

Insecticides can provide good control of E. tuberis (Antonelli and Davidson, 1991; Vernon and Mackenzie, 1991a, b). Synthetic pyrethroids are particularly effective. Chemicals routinely used against aphids on seed potatoes are also effective against adult E. tuberis and prevent leaf damage due to adult feeding. It is more difficult to control E. tuberis larvae since they are in the soil and insecticides incorporated into the soil may fail to provide adequate protection (Finlayson et al., 1979) although expensive granular formulations can be used. When overwintered populations are kept under control, localized sprays and targeting field edges, from where most overwintered adults will emerge, may be all that is necessary to provide effective control.

E. tuberis developed resistance to a number of organochlorines developed in the 1960s (Campbell and Finlayson, 1976). Organophosphates were used to provide control in the 1970s (Finlayson et al., 1972). Given the history of developing insecticide resistance, there is a possibility that resistance to modern insecticides may develop.

Phytosanitary Methods

Phytosanitary control to prevent the international spread of E. tuberis includes the restriction or prohibition of the importation of soil, or plants with soil, from countries where E. tuberis occurs (OEPP/EPPO, 1989). More specifically, when importing potato tubers from countries where E. tuberis is known to occur, appropriate phytosanitary measures should be used (OEPP/EPPO, 1990).