Distribution. Several native species of Tenebrio-nidae damage vegetable crops in the western United States and Canada. The affected area is west of the Mississippi River, and invariably is arid. Although numerous species may be involved, the common species and area where damage has been reported are: Blapstinus elongatus Casey (California), B. fuliginosus
Casey (California), B. pimalis Casey (Arizona, California), B. rufipes Casey (California), B. substriatus Champion (Montana), Coniontis globulina Casey (California), C. muscula Blaisdell (California), C. subpubescens LeConte (California), Eleodes hispilabris Say (Alberta, Washington), E. omissa (Say) (California), E. tricostatus (Say) (western United States and Canada), and Ulus crassus (LeConte) (California). The list of damaging species is likely longer, but species-level identifications are not usually made. In fact, these insects commonly are confused with wireworms (Coleoptera: Elateridae), a similar and much more common group of pests.
Host Plants. False wireworms are associated with grassland environments, and both larvae (called false wireworms) and adults (called darkling beetles) feed on seeds and seedlings of grasses and grain crops. Most false wireworm species, including many which are not mentioned above, are best known as wheat pests, principally because this is the crop most often grown in the arid areas inhabited by these insects. However, when irrigation is applied and vegetable crops cultured, false wireworms may also cause injury to vegetables. Among the vegetables reported injured are asparagus, cabbage, cantaloupe, corn, lettuce, lima bean, mustard, onion, pepper, potato, radish, snap bean, tomato, and watermelon.
Natural Enemies. Many parasitoids and diseases are known from false wireworms and darkling beetles, but the significance of these natural enemies is not always apparent. Flesh flies (Diptera: Sarcophagidae), particularly Blaexoxipha eleodes (Aldrich), are known from several Eleodes spp. Eleodes spp. also are parasitized by Eleodiphaga and Sitophaga spp. (Diptera: Tachinidae) and Microctonus eleodis (Viereck) (Hyme-noptera: Braconidae). The fungi Beauveria bassianna and Metarhizium anisopliae occasionally are associated with false wireworm larvae (Allsopp, 1980).
Rodents are important predators of darkling beetles in grass and shrub ecosystems, but not all rodent species consume them regularly. Work in Utah indicated that though northern grasshopper mouse, Onychomys leucogaster arcticeps, and omnivorous deer mouse, Peromyscus maniculatus nebrascensis, were effective predators, Uinta ground squirrel, Spermophilus armatus, and Great Basin pocket mouse, Perognathus parvus clarus, developed an aversion to the beetles after several feedings (Parmenter and MacMahon, 1988).
Birds feed readily on larvae and pupae, and often follow tractors as the soil is tilled, and capture the exposed insects. Larvae also can be forced to the soil surface when it becomes saturated by heavy rain, and birds are frequently observed to take advantage of this temporary abundance of food. Consumption of the adult stage is more infrequent, but some species are adapted to consume these insects. Among the species which feed on darkling beetles most frequently are bronzed grackle, Quiscalus quiscula seneus; western crow, Corvus brachyrhynchos hesperis; western robin, Planesticus migratorius propinquus; and sage hen, Centrocercus urophasianus (Hyslop, 1912c)
Life Cycle and Description. The aforementioned false wireworm species have, at most, a single generation per year. Most species seem to require 2-3 years to complete their development. False wireworms generally overwinter as larvae, but some species pass the winter as adults. Some apparently overwinter in both stages.
The life cycle of Eleodes hispilabris, one of the most common species that affect vegetables, is fairly typical of false wireworms. Adults pass the winter under dense masses of leaf debris, in cracks in the soil, and in rodent burrows. In the spring the adults feed on young weeds. In June they commence egg laying, with eggs deposited just beneath the soil surface. The eggs hatch in July, with the larvae about one-half grown at the onset of winter. The larvae commence feeding again in the spring, and pupate in the soil in about August. They have about 11 instars, and duration of the larval stage is about 270 days. The adults emerge in the autumn, feed briefly, and then overwinter, completing the two-year developmental cycle.
The species differ somewhat in appearance, but the following description of Eleodes letcheri Blaisdell is typical. The egg is oval, measuring about 1.1 mm long and 0.6 mm wide. It is white, and free of sculpturing. Larvae are elongate-cylindrical, and somewhat flattened ventrally. Larvae are yellowish, but the head, mandibles, tarsi, and anal segment are brown to black. The antennae are short, enlarged or clubbed at the tip, and yellow in color. The enlarged antennae of false wireworms serves to differentiate them from wireworms, which lack expanded antennae. The thoracic legs are stout. The larvae move freely and rapidly on the soil surface, a characteristic that helps distinguish them from wireworms, which are not agile on the soil suface. The pupa generally resembles the adult, except that the elytra are shrunken. Initially white in color, the pupal stage soon turns black. The adult is a shining black beetle with punctate elytra. The legs are long and stout. The maximum width of the abdomen is considerably greater than the juncture of the thorax and abdomen, and the tip of the abdomen tapers to a point. The adults are easily distinguished from predatory ground beetles (Coleoptera: Carabidae), with which they could be confused, because the apical segments of the antennae are enlarged in tenebrionids but not in carabids.
Most adults measure about 2.5 cm long. They display a defensive posture that involves extending the hind legs and tilting the body forward so that the tip of the abdomen is greatly elevated. Release of chemical exudates usually accompanies the head-standing behavior. In some cases the exudate is forcibly expelled, but more commonly it is simply released at the tip of the abdomen as a drop, or spreads over the posterior part of the body. The exudate usually contains toluqui-none, ethyl-p-quinone, and often other chemical components, that help deter predation.
A worldwide review of false wireworm biology was published by Allsopp (1980). Observations on several western species were provided by Wakeland (1926). Rearing was outlined by Matteson (1966) and Wright (1972).
These insect normally are pests of dryland agriculture, and particularly of fields that have recently been converted from grassland. However, as noted by Daniels (1977), irrigated crops can be invaded. Both larval and adult stages may injure vegetables, but such injury is infrequent. Larvae tend to reside in the soil near the surface and feed on roots, seeds, and the stems of seedlings. Farmers often first detect a false wire-worm infestation when they observe an irregular or patchy stand of seedlings in a field; widespread or uniform damage is rare. The adults are more mobile and active above-ground, they often feed on aerial plant parts. For example, Campbell (1924) observed the beetles feeding on the stems of tomatoes, peppers and lima beans—both young seedlings sprouting from seed and transplanted plants were injured. Such injury is usually inflicted at the soil surface, and sometimes several beetles aggregate and feed on a single plant, quickly girdling it. Older plants are quite resistant to attack. False wireworms are omnivorous. In addition to feeding on seeds and seedlings, they also may feed on tubers, leaf tissue, plant detritus, and insect cadavers. Toba (1985a) studied damage to potato in Washington and reported that the surface scarring inflicted on potatoes was so minor that it would not lower the grade, and reduce the value, of potatoes.
Cultural Practices. Soil characteristics are often linked to false wireworm problems, with damage most often occurring in dry, light, sandy or sandy loam soil (Wade, 1921). However, research in South Dakota showed that though some species (e.g., E. hispilabris) were most frequent in such soil types, other species (e.g., E. tricostatus) occur across most soil types, including heavier clay soils (Calkins and Kirk, 1975).
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