Distribution. Wheat wireworm is northern in distribution, but occurs primarily in eastern North America. This native wireworm is considered to be a pest from the Atlantic Ocean to the Great Plains, and damaging as far west as eastern Saskatchewan. It is considered to be the most serious wireworm pest in Canada's Atlantic Provinces, and is well known in the midwestern states. It is not the only Agriotes spp. that is known to damage crops, but it is the most serious. Among other Agriotes spp. that sometimes damaging are dusky wireworm, A. obscurus (Linnaeus) and lined click beetle, A. lineatus (Linnaeus), both imports from Europe to the east and west coast of Canada; western wireworm, A. sparsus LeConte, known to damaging in the northwest; and A. sputator (Linnaeus), another European import that inhabits eastern Canada.
Host Plants. This species is known to feed on such vegetables as bean, cabbage, carrot, corn, cucumber, potato, tomato, turnip, and probably others. As its common name suggests, A. mancus is a pest of wheat, and it also damages such field crops as oats, soybean, and tobacco. It favors many grasses, and as is the case with many wireworms, crops are often damaged when planted after grass sod.
Natural Enemies. There is little information on the natural enemies of wheat wireworm. Avian predators are sometimes observed feeding on larvae exposed by tillage, but birds probably affect a small proportion of the population. Fungi are commonly associated with dying or dead wireworms, but their role in wireworm ecology is poorly known.
Life Cycle and Description. Wheat wireworm has a 3-4 year life cycle. Adults are active early in the spring, mate, and oviposit in April or May. Larvae feed through the remainder of the first year, and the entire second year, overwintering as partly grown larvae. During the third season they complete larval growth and pupate in July, forming adults in August-October. The adults remain in the soil, in their pupal cells, until the following spring. In New York, a portion of the population has an extended larval development time, producing a four-year cycle (Rawlins, 1940). Under the cooler conditons of Quebec, apparently all insects have a four-year life cycle (Lafrance, 1967).
A detailed description of the morphology and biology of wheat wireworm was provided by Hawkins (1936), and good life-history information was given by Rawlins (1940). A key to distinguish Agriotes from the other common vegetable-attacking genera of wireworms can be found in Appendix A. Keys for
the identification of the genera of adult Elateridae can be found in Arnett (1968), and of larvae in Wilkinson (1963) and Becker and Dogger (1991). Although Wilkinson (1963) did not include A. mancus in his key to wireworms of British Columbia, it is very useful for identification of the other western Agriotis spp. Becker (1956) also provided a major review of the genus Agriotes. Thomas (1940) provides a review of wireworm biology and management, and King (1928a) and Glen et al. (1943) gave useful information on wireworm ecology and damage in Canada.
Injury by wheat wireworm is typical of wireworm damage. Larvae feed below-ground on roots, stems, stolons, and tubers. They may tunnel completely through large plant tissue such as potato tubers, which are honeycombed by their feeding passageways. In other instances the larvae limit themselves to surface feeding, which nevertheless mar the appearance and reduce commercial value. Once the larvae chew through the surface, the tissue is often invaded by fungi and other soil-borne plant pathogens.
Sampling. The eggs can be separated from the soil by sifting with a 60-mesh sieve. Separation is aided by a gentle stream of water, which helps wash away the soil, including some of the soil particles that adhere to the sticky surface of the eggs. They also can be separated by flotation, using a strong solution of sodium chloride or magnesium sulfate.
Population monitoring depends primarily on assessment of larval populations, and fields should be sampled before susceptible crops, such as potatoes, are planted. Larval populations are sampled by baiting or soil sampling. Baiting is accomplished by burying whole wheat, corn, barley, flour plus molasses, or other attractive food sources in the soil at a depth of 10-15 cm and counting the number of wireworm larvae attracted (Lafrance, 1967; Parker, 1994). Baiting does not work well if the soil is cold, so a sheet of black or transparent plastic is sometimes placed over the section of soil containing bait; this warms the soil and increases the mobility of wireworm larvae, allowing more accurate counts. Simmons et al. (1998) compared several methods of sampling and reported that corn/wheat baits were the most accurate, precise, and cost effective.
For soil sampling, 15 x 15 cm soil samples, including soil to a depth of 30-40 cm, are removed and checked for wireworms. This is normally done by sieving with coarse and fine screen to separate insects from the soil. Although accurate estimates of wireworm population densities are possible with soil sampling, this approach is very labor intensive; however, baiting is more commonly used.
Adults may be collected from "trap heaps," which consist of small piles of hay placed on bare soil. They are made more attractive by spraying the heap with a solution of dilute molasses. Unlike many other click beetle species, A. mancus cannot be readily captured in blacklight traps, apparently because the beetles disperse primarily by walking (Lafrance, 1967).
Insecticides. Insecticides are often applied for wireworm control when susceptible crops such as potato are planted. Insecticides may be applied broadcast before planting, but more commonly are applied at the time of planting in the seed furrow, over the row, or broadcast. At low wireworm densities, applications limited to the rows are adequate, but at moderate wireworm densities broadcast applications are often more effective. At high densities susceptible crops should not be planted.
Cultural Practices. Land management has a significant role in creating or alleviating problems with wheat wireworm. Land that is planted to grass sod is often heavily infested with wheat wireworm, and crops are at great risk for about 2 years following conversion from sod to crops. Also, this wireworm is usually associated with heavy soil such as silt and clay loams, and low-lying or moist sections of fields.
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