Food and oviposition preferences of Diabrotica v. virgifera in multiple-choice crop habitat situations

Multiple-choice field cage experiments were used to clarify to what extent adults of one of the most destructive maize pest, the western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), use non-maize crop habitats as alternative food sources or oviposition sites in situations of non-maize/maize rotations. Between 2009 and 2012, D. v. virgifera adults were released into large walk-in gauze cages each containing different combinations of three out of ten crop habitats in southern Hungary. Maize was planted the following year, allowing the development of larvae and the emergence of adults that were then captured in small cages. Results indicate that the polyphagous nature of D. v. virgifera adults is, under field situations, not as important as often stated. The generational, i.e. annual growth rate of populations, an indicator of crop habitat quality for food and oviposition, appeared highest when the entire multiple-choice cage had been planted with maize (populations nearly doubled). When Sudan grass and Sorghum millet were combined with maize, a slight population grow was still possible. When maize was combined with any other habitat type, populations decreased from year to year, suggesting that non-maize crop habitats are suboptimal, and their role as alternative food sources under field conditions might be overestimated. As for oviposition, also maize was found to be the most attractive. Of medium proportional attractiveness for oviposition were Sorghum millet, Sudan grass, and ploughed bare soil. Harvested and grubbed winter rape with some regrowth, harvested and grubbed or not grubbed winter-wheat with regrowth, and potatoes were comparatively less attractive for oviposition, suggesting that regrowth or volunteer crops play no role for D. v. virgifera. Least suitable were harvested and grubbed peas and soybean. The presence of particular weed species had no detectable influence on oviposition, but vegetation coverage of crops and/or weeds positivity influenced oviposition. In conclusion, there is no indication that the rotation-tolerant D. v. virgifera strain had been introduced from the USA. Crop rotation, no matter what crop combination in an agricultural area, remains an effective control measure for D. v. virgifera populations in Europe, and should be communicated as such by regional or country wide decision makers in agri-policy.