A regional view of an impending invasion: western corn rootworm development in Northern Germany

We examined the immature development of the invasive maize pest western corn rootworm (Diabrotica virgifera virgifera LeConte; WCR) under Northern German temperature regimes. This research was part of the Climate impact and adaptation research in Lower Saxony, Germany (KLIFF; Klimafolgenforschung in Niedersachen), funded by the Ministry for science and culture of Lower Saxony. The experiments were conducted under quarantine conditions in climatic cabinets. Aim of the study was an improved knowledge of western corn rootworm biological key data under regional conditions which were necessary for an adequate integrated pest management strategy. This thesis adresses three fundamental issues: 1. Does a by 2 weeks delayed sowing date under recent temperature regime or a warmed temperature regime influence WCR development by disrupting host-pest synchronity? The temperature regime did not influence hatching rates, but the time of mean hatch occured earlier (JD 177) under the warmed temperature regime compared to JD 195 under today's temperature regime. Under the warmed regime larval development was retarded at the late sown plants. 2. We evaluated the effects of varying day-night (4°C and 6°C difference) temperature regimes compared to the equivalent constant temperature regimes on WCR immature development. Varying day-night temperatures resulted in earlier larval hatch and accelerated larval development. This effect was fortified at the higher temperature difference regime. For WCR the temperature sum needed for hatch in the field are overestimated when they are determined by models based on constant experimental temperatures. 3. We tested for developmental differences between the US non-diapausing laboratory population and two European field populations from Serbia and Hungary under a Northern German temperature regime. Hungarian and Serbian populations showed slight higher temperature requirements compared with the laboratory population. The Hungarian population required most thermal energy for hatch. We assumed that the differences between the two field populations indicate a rapid adaptation process of the introduced population. The benefits of the non-diapausing laboratory population are very high. For our comparing studies of the WCR traits hatching rate, development and recovery the US non-diapausing laboratory population was a very useful organism.. The earlier hatch has to be considered in comparison to field populations. For the implementation of regional pest management strategies local populations should be used in further experiments.