Movement Ecology of Adult Western Corn Rootworm: Implications for Management

Abstract

Movement of adult western corn rootworm, Diabrotica virgifera virgifera LeConte, is of fundamental importance to this species’ population dynamics, ecology, evolution, and interactions with its environment, including cultivated cornfields. Realistic parameterization of dispersal components of models is needed to predict rates of range expansion, development, and spread of resistance to control measures and improve pest and resistance management strategies. However, a coherent understanding of western corn rootworm movement ecology has remained elusive because of conflicting evidence for both short- and long-distance lifetime dispersal, a type of dilemma observed in many species called Reid’s paradox. Attempts to resolve this paradox using population genetic strategies to estimate rates of gene flow over space likewise imply greater dispersal distances than direct observations of short-range movement suggest, a dilemma called Slatkin’s paradox. Based on the wide-array of available evidence, we present a conceptual model of adult western corn rootworm movement ecology under the premise it is a partially migratory species. We propose that rootworm populations consist of two behavioral phenotypes, resident and migrant. Both engage in local, appetitive flights, but only the migrant phenotype also makes non-appetitive migratory flights, resulting in observed patterns of bimodal dispersal distances and resolution of Reid’s and Slatkin’s paradoxes.

Critical Facets of European Corn Borer Adult Movement Ecology Relevant to Mitigating Field Resistance to Bt-Corn

“…Thus, European corn borer migration is not characterized by the mass springtime exodus from overwintering grounds and mass arrival in a disjunct breeding range that makes a migration event so obvious for seasonal migrants like black cutworm ( Agrotis ipsilon ) [ 120 ], fall armyworm ( Spodoptera frugiperda ) [ 121 , 122 ], monarch butterfly ( Danaus plexippus ) [ 123 , 124 ], and many others [ 125 ]. Instead, migration is almost invisible for an insect like European corn borer, which departs and arrives where others of its kind are simultaneously arriving and departing [ 89 , 126 , 127 ]. There is no spatial goal to which they orient, so the direction the moths travel is dependent on wind direction on the night of ascent into the atmosphere.…”

“…This result contrasted with that for western corn rootworm ( Diabrotica virgifera virgifera , Coleoptera: Chrysomelidae), densities of which were significantly correlated with corn use in the landscape at 1-km and 20-km radii [ 96 ]. Western corn rootworm is also a partial migratory species, but with only about 25–30% of adults emigrating from the natal field before or in the midst of reproduction [ 127 ]. The 12 km radius, or whatever radius is chosen, may need to extend from the edge of the spatial extent of early warning resistance rather than from the area of observed practical resistance.…”

Corn Rootworm: Biology, Ecology, Behavior, and Integrated Management

“…The highly adaptable nature of this species has made management an ongoing challenge. Over time, this species has evolved resistance to active ingredients in four insecticide classes, annual crop rotation, and all commercially available rootworm-active Cry toxins (derived from the soil microbe Bacillus thuringiensis) expressed in Bt-maize hybrids in the U.S.A. [4][5][6].…”

“…This requires movement away from single-tactic approaches to a combination of tactics deployed within an integrated pest management framework [5]. This will include the conceptualization and development of new tactics that are based on an increased understanding of Diabrotica biology, physiology, ecology, and population dynamics [6][7][8][9][10].…”

“…[1];• The biology and management of D. v. virgifera in Europe[3] and D. speciosa (Germar), D. balteata (LeConte), and D. viridula (F.) in South America[2]; • Host-microbe relationships and aspects of chemical ecology that influence D. v. virgifera behavior and host plant resistance[9]; • The movement ecology of D. v. virgifera and its relation to management[6];…”