Northern corn rootworm

Appearance

Body length 4.8-5.6 mm. Body width 2.0-2.5 mm. Head basic color yellow. Antennae filiform, bi- or tricolored, antennomere 1 yellow, testaceous or greenish brown, antennomeres 2-11 brussels brown. Maxillary palpi and labrum black or piceous. Pronotum paris green, green or yellow, quadrate, deeply bifoveate, not shagreened. Scutellum yellow or amber yellow. Elytra green, sometimes humeri and basal third of suture tinged with amber, with five distinct sinuate sulci, strongest behind the humeral callus and extending beyond the middle. Elytral epipleura green, sutural angle of elytra round, punctation scattered, fine. Abdomen yellow, pale olivine or green. Tarsi black, amber brown or chestnut. Tibiae bicolored yellow, outer edge with piceous or testaceous line, or extensively darkened. Femora uniform yellow or olive ocher. Aedeagus symmetric, with four internal sac sclerites.

Naming

Diabrotica barberi R. Smith & Lawrence 1967

Diabrotica barberi Smith & Lawrence (the northern corn rootworm) was originally described as Galleruca longicornis by Say in 1824 and was subsequently transferred to the genus Diabrotica Chevrolat, 1843, considered only as a subspecies of Diabrotica longicornis (Say). However, based on laboratory and field studies, Krysan et al. (1983) elevated the taxon to species level. They concluded that even when the two species occur in the same geographic areas, adults are found in different habitats and they show a clear sexual isolation that supports the decision to elevate D. barberi to the species level.

Distribution

CANADA: Manitoba, New Brunswick, Ontario, Quebec
USA: AL, AR, CO, CT, DE, GA, IL, IN, IA, KS, KY, MD, MA, MI, MN, MO, NE, NH, NJ, NY, NC, ND, OH, OK, PA, RI, SC, SD, TN, VT, VA, WV, WI.

Reproduction

Two species of Diabrotica have evolved resistance to crop rotation that involves planting the same primary crop every second year in the same location. Diabrotica barberi has adapted by extending egg diapause for more than one winter.

Diabrotica barberi displays a single generation per year, with the egg stage overwintering but a portion of eggs within the population show an extended diapause trait that causes eggs to overwinter for 2 years and occasionally even for 3–4 years (French et al., 2014).

Eggs are laid in sets of 25–31 eggs by the female and hatch in late spring and early summer. Larvae feed on the roots of maize where they have three instars (Hammack et al., 2003). Development from egg to adult can be completed in laboratory studies in the range 15–31.5°C and the lower developmental threshold is estimated to be 10.2°C with 865 accumulated degree-days (base 10.2°C) needed from hatching to adult appearance in the field (Woodson and Jackson, 1996). Upon emergence from the soil, adults feed on maize tassels, silks and ear tips. Adult populations peak in the fields while maize is flowering (Lance et al., 1989). As the floral structures of maize dry, females abandon maize fields (Lance et al., 1989) and become increasingly abundant on the flowers of weeds, prairie forbs and crops other than maize listed above. According to Naranjo and Sawyer (1987), mean female and male longevity were similar, ranging from approximately 90 days at 17.5°C to 42 days at 30°C.

Food

Feeds on plants in several families including maize (Zea mays L.) and other grasses (Poaceae), Cucurbitaceae, Asteraceae and Fabaceae.

Adults show a comparable range of host preference, with corn kernels, corn silk and corn tassel tissue favouring survival and reproduction, but maize leaves are not the preferred food of adults (Ludwig and Hill, 1975). Blossoms from Solidago canadensis, Cucurbita spp. and Helianthus annuus are also suitable. Additionally, adults feed on pollen from plants in the families Gramineae, Compositae, Leguminosae, and Cucurbitaceae.

Host list: Agropyron cristatum, Bouteloua curtipendula, Bouteloua dactyloides, Elymus canadensis, Elymus smithii, Elymus trachycaulus, Eragrostis curvula, Hordeum vulgare, Oryza sativa, Panicum miliaceum, Setaria helvola, Setaria viridis, Sorghastrum nutans, Spartina pectinata, Thinopyrum elongatum, Thinopyrum intermedium subsp. intermedium, Thinopyrum intermedium, Triticum aestivum, Triticum spelta, Zea mays

Evolution

Some Northern Corn Rootworm populations are adapted to crop rotation by expressing an extended diapause trait that delays embryonic development for 2 years.