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A soil washing apparatus was constructed and tested in collaboration with colleagues from the grant authority and project partners in Austria and Romania. It is based on a similar apparatus used in the USA but our apparatus can quickly process a large number of samples. The eggs were extracted by sieving and then floating on MgSO4-solution followed by sedimentation in water. Eggs of D. virgifera virgifera were separated from those of other species by studying the structure of egg surface. The efficiency of extraction of the apparatus was checked using samples spiked with blue coloured eggs. In co-operation with Austrian and Romanian colleagues a method was developed for sampling in the field. Eggs of D. virgifera virgifera were extracted from soil samples collected from fields in Austria and Romania in spring/summer and autumn 2011. The beetles did not appear to prefer to lay eggs at either the edges or centres of fields. As very few eggs were found at the edges of oil seed squash fields this crop does not appear to be a suitable habitat for egg laying.

The objective of this study was to obtain data that could be used to develop a model for forecasting the occurrence of Diabrotica virgifera virgifera. The model currently available is mainly based on results from American studies using non-diapausing beetles, but the biological performance (fitness and mobility) of American nondiapausing beetles and those of European origin could differ, which would affect the accuracy of this model when used for forecasting in Europe. Thus, it is important to know whether the biological performance of D. virgifera virgifera of European origin differ from that of non-diapausing American beetles. The following aspects of the effect of temperature on the biology of D. virgifera virgifera occurring in Europe were studied and compared with those of a non-diapausing strain from the US: - pre-diapause development of eggs, - post-diapause development of eggs, - effect of different temperatures and densities on the development of larvae. The results indicate that the American data based on studies of non-diapausing strains of D. virgifera virgifera are of only limited use for forecasting the occurrence of this pest in Europe. In particular, the results obtained for the development of eggs, larvae and adults provide information about this species’ biology that could be used to increase our understanding of the population dynamics of this pest in Europe.

In a series of greenhouse experiments the host status and quality of 49 biofuel plants for the larvae of WCR were evaluated. The plants tested (18 species and varieties of Sorghum, 16 forage grasses, 6 Miscanthus genotypes, 6 Panicum varieties and 3 broadleaf species) were grown for at least three weeks before they were used in the bioassays. The insects used in the experiments were obtained from a non diapausing laboratory strain originally from the US and maintained by BTL since 2006. Only neonate larvae (not older than 24 hours) were used in the bioassays. In each experiment up to six species or varieties of plants were tested each with 10 replicates (containers). A susceptible maize variety was used as a positive control in each experiment. Each plant container was infested with ten neonate WCR larvae using a fine art brush. After inoculation the plants were not watered for at least 24 hours to facilitate the establishment of the larvae. The experiments were terminated after 18 days. To extract surviving larvae the soil and roots of test plants were carefully examined by hand and then transferred to a modified MacFadyen heat extractor with an extraction temperature of 45 °C. To assess the host quality the number of larvae recovered, the widths of their head capsules and dry weights were recorded. The larvae were dried at 40 °C for at least 72 hours and then weighed on an electronic micro balance. Of the 21 forage and switch grasses examined 16 hosted WCR larvae. However, the percentage of larvae that survived for 18 days, their dry weights and head capsule widths were significantly less than that recorded for larvae that developed on maize roots. The roots of most (i.e. 15) of the 18 Sorghum species or varieties tested were unsuitable for the development of WCR larvae. For the remaining three Sorghum species a maximum of only two larvae (of 100 inoculated) were recovered. These results indicate that species of Sorghum are very poor quality hosts for WCR as previously reported in other studies. The opposite was true for the Miscanthus species tested. The number of larvae recovered from Miscanthus x giganteus roots, their dry weight and head capsule widths were the same as those recorded for larvae reared on the maize control. The other Miscanthus genotypes were less suitable than Mxg, but still more acceptable than all the forage and switch grasses tested in this study. In accordance with all previous studies, which used host plants other than maize, no larvae developed on the three broad leaf species.

Due to the great ecological plasticity and adaptability of the western corn rootworm, Diabrotica virgifera virgifera LeConte, the unilateral use of one control option could result in it becoming less effective within a few years. Therefore, no one option alone is sufficient for resolving the problem with D. virgifera virgifera. In fact all possibilities have to be considered and integrated. One possibility is to control the adult beetles and so minimize egg deposition and reduce the beetle population size below the economic threshold for the following year. By applying mixtures of insecticides with bitter substances from cucurbits, which are strong feeding stimulants for D. virgifera virgifera, it should be possible to reduce insecticide dosages by up to 95%. This would control the beetles and minimize undesired side-effects to the agro-ecosystem and non-target organisms. Therefore, the aim of this study was to determine (i) the interactions between cucurbitacins (Invite) and five insecticides with different odes of action (indoxacarb, neonicotinoids, organophosphates, pyrethroids and spinosyns), (ii) the effects of biological factors (age, gender and pre-contact) and (iii) the possibility of selection for resistance to bitter agents. In laboratory trials it was shown that the stimulatory effect Invite has on feeding had little or no effect on the efficacy of the five insecticides tested. The improvement in the efficacy after five hours of exposure to Avaunt (indoxacarb) and Biscaya (neonicotinoid) disappeared after 24 and 48 h, and is attributed to the slow initial effects of Avaunt and the recovery of beetles exposed to Biscaya, respectively. Although the LC-values of Biscaya and Avaunt were significantly greater than the corresponding values for mixtures with Invite, it was not possible to reduce the dosages of these active substances by up to 90%. There was no improvement in the efficacy after 48 h of exposure to any of the other insecticides analyzed. The assumption that contact (e. g. pyrethroides) and gas phase insecticides (e. g. organophosphate) are generally less suitable for mixing with Invite was only partly supported by our results. The lack of improvement in the efficacy of Spinosad when mixed with Invite is especially puzzling. Neonicotinoids and indoxacarb are suitable for mixing with Invite, especially in terms of delaying the selection for resistance. Carbamates, e. g. carbaryl (not analyzed in this study), were successfully applied in mixtures with cucurbitacins. The results indicate that biological factors such as gender, age and pre-contact have a strong effect on the attractiveness of Invite. In the experiments, the strength of the response of young beetles to the bitter agents was greater than that of old beetles and that of females less intense than that of males, and pre-contact markedly reduced the stimulatory effect for both sexes. These results and the findings of trials using D. virgifera virgifera caught in Austrian maize fields before and after applications of insecticide-Invite mixtures indicate that the attractiveness of cucurbitacins varies and is subject to selection. If this control strategy is applied extensively then it is likely that this beetle will develop resistance to the bitter agents. Thus, it is important to monitor the resistance of the beetles to these substances.

Abstract: Pollen beetles (Nitidulidae: Meligethinae) are among the most abundant flower-visiting insects in Europe. While some species damage millions of hectares of crops annually, the biology of many species is [...]