Western Corn Rootworm (Diabrotica virgifera virgifera LeConte) in Europe: Current Status and Sustainable Pest Management

Western corn rootworm (WCR), or Diabrotica virgifera virgifera LeConte, became a very serious quarantine maize pest in Europe in the mid-1990s. Between 1995 and 2010, European countries were involved in international projects to share information and plan common research for integrated pest management (IPM) implementation. Since 2011, however, common efforts have declined, and an overview of WCR population spread, density, and research is in serious need of update. Therefore, we retained that it was necessary to (1) summarize the research activities carried out in the last 12 years in various countries and the research topics addressed, and analyze how these activities have contributed to IPM for WCR and (2) present the current distribution of WCR in the EU and analyze the current population levels in different European countries, focusing on different management strategies. A review of scientific papers published from 2008 to 2020, in addition to direct interviews with experts in charge of WCR management in a range of European countries, was conducted. Over the past 12 years, scientists in Europe have continued their research activities to investigate various aspects of WCR management by implementing several approaches to WCR control. A considerable amount of new knowledge has been produced, contributing to the development of pest management strategies applicable in EU farming systems. Among the 10 EU countries analyzed, there is no country reporting economic damage on a large scale. Thanks to intensive research leading to specific agricultural practices and the EU Common Agricultural Policy, there are crop-rotation-based solutions that can adequately control this pest avoiding insecticide use.

Western Corn Rootworm, Plant and Microbe Interactions: A Review and Prospects for New Management Tools

The western corn rootworm, Diabrotica virgifera virgifera LeConte, is resistant to four separate classes of traditional insecticides, all Bacillius thuringiensis (Bt) toxins currently registered for commercial use, crop rotation, innate plant resistance factors, and even double-stranded RNA (dsRNA) targeting essential genes via environmental RNA interference (RNAi), which has not been sold commercially to date. Clearly, additional tools are needed as management options. In this review, we discuss the state-of-the-art knowledge about biotic factors influencing herbivore success, including host location and recognition, plant defensive traits, plant-microbe interactions, and herbivore-pathogens/predator interactions. We then translate this knowledge into potential new management tools and improved biological control.

The Use of Insecticides to Manage the Western Corn Rootworm, Diabrotica virgifera virgifera, LeConte: History, Field-Evolved Resistance, and Associated Mechanisms

The western corn rootworm, Diabrotica virgifera virgifera LeConte (Dvv) is a significant insect pest of maize in the United States (U.S.). This paper reviews the history of insecticide use in Dvv management programs, Dvv adaptation to insecticides, i.e., field-evolved resistance and associated mechanisms of resistance, plus the current role of insecticides in the transgenic era. In the western U.S. Corn Belt where continuous maize is commonly grown in large irrigated monocultures, broadcast-applied soil or foliar insecticides have been extensively used over time to manage annual densities of Dvv and other secondary insect pests. This has contributed to the sequential occurrence of Dvv resistance evolution to cyclodiene, organophosphate, carbamate, and pyrethroid insecticides since the 1950s. Mechanisms of resistance are complex, but both oxidative and hydrolytic metabolism contribute to organophosphate, carbamate, and pyrethroid resistance facilitating cross-resistance between insecticide classes. History shows that Dvv insecticide resistance can evolve quickly and may persist in field populations even in the absence of selection. This suggests minimal fitness costs associated with Dvv resistance. In the transgenic era, insecticides function primarily as complementary tools with other Dvv management tactics to manage annual Dvv densities/crop injury and resistance over time.

Models of Diabrotica Populations: Demography, Population Genetics, Geographic Spread, and Management

Both Diabrotica virgifera virgifera LeConte and D. barberi Smith and Lawrence are among the most damaging insects impacting corn in North America. D. virgifera virgifera has also invaded Europe and has become an important pest in that region. Computer models have become an important tool for understanding the impact and spread of these important pests. Over the past 30 years, over 40 models have been published related to these pests. The focus of these models range from occupancy models (particularly for Europe), impact of climate change, range expansion, economics of pest management, phenology, to the evolution of resistance to toxins and crop rotation. All of these models share characteristics. We elaborate on the methods in which modelers have incorporated the biology of these pests, including density-dependence, movement, fecundity and overwintering mortality. We discuss the utility of both spatially-explicit, complex models and spatially-implicit, generational models and where each might be appropriate. We review resistance models that either explain past evolution to crop rotation, insecticides or insecticidal traits or attempt to predict the consequences of resistance management strategies.

Inheritance and Fitness Costs of Cry3Bb1 Resistance in Diapausing Field Strains of Western Corn Rootworm (Coleoptera: Chrysomelidae)

Field-evolved resistance to Cry3Bb1 corn by western corn rootworm, Diabrotica virgifera virgifera LeConte (Colleoptera: Chrysomellidae), has been reported in field populations in Iowa, Illinois, Nebraska, and Minnesota. Inheritance and fitness costs associated with Cry3Bb1 resistance have been determined for non-diapausing laboratory strains of western corn rootworm with either laboratory-selected resistance or field-derived resistance. However, information on inheritance and fitness costs of Cry3Bb1 resistance in the diapausing field populations is lacking. In this study, we determined the inheritance of Cry3Bb1 resistance for four diapausing field strains of western corn rootworm using plant-based bioassays. We also determined the fitness costs for eight diapausing field populations in a greenhouse experiment. We found that Cry3Bb1 resistance was an autosomal trait and that the inheritance of resistance was mostly non-recessive; however, there was some variation in the dominance of Cry3Bb1 resistance. We did not find evidence of fitness costs affecting survival to adulthood, developmental rate, or adult dry mass. However, we did detect a fitness cost affecting adult size. The results of this study will add to the current understanding of field-evolved resistance to Cry3Bb1 corn by western corn rootworm and help in developing better strategies to manage resistance.