41st Annual Meeting of the Society for Invertebrate Pathology
and 9th International Conference on Bacillus thuringiensis

The Western Corn Root Worm (Diabrotica v. virgifera) first time occurred in Germany in July 2007. Four different maize cultivars including Diabrotica-resistant MON88017, were assessed in respect to its effects on saprophagous Diptera and predators out of Carabidae and Staphylinidae. The methodological approach comprised a hierarchic order of different ecological scale levels (agro-ecosystem, population, organisms). Abundance and species composition of both Diptera and their predators were recorded in the field. Most saprophagous Diptera belong to Sciaridae (fungus gnats), of which the predominant Lycoriella castanescens was used for feeding trials. It was tested whether mortality, pupation, hatching rates, duration of larval development and pupation were affected by uptake of Cry3Bb1-contminated plant tissues. Species of Carabidae and Staphylinidae were fed with Sciaridae-larvae reared on Bt- and non-Bt-maize-litter respectively. In a similar way Diabrotica-larvae were offered as prey. Toxin analyses of saprophagous Diptera and predators reared with Bt-plant parts or feeding on Bt-contaminated prey contained Bt-toxin up to 1.6% (decomposers) and 14.0% (predators) of the toxin level recorded in the source material. Predators collected from Bt-maize fields stated these findings. Thus, Bt-toxin is transferred into the food chain. Predators feeding on prey containing Cry3Bb1-toxin showed a significant delay in accepting the prey in comparison to prey free of Bt-toxin, but this didn't result in higher mortality or less longevity. However, predators which were fed with Sciaridae-larvae containing Bt-toxin produced significantly less offspring than those feeding on prey reared with non-Bt-maize litter. Thus, an uptake of Cry3Bb1-toxin by carnivorous beetles doesn't lead to a higher mortality, but results in subtle effects like lower fertility of the females.

Currently, all commercialized transgenic approaches for managing western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, and northern corn rootworm, Diabrotica barberi Smith and Lawrence, in the USA utilize various Bt proteins as the insecticidal mode of action. While this approach has proven to be an excellent tactic for maize producers in the USA, additional modes of action will likely be required to ensure the long term success of transgenic approaches for rootworm management. We recently reported that ingestion of dsRNAs from selected target gene templates can induce larval stunting and mortality in artificial feeding assays. Furthermore, we demonstrated that maize plants expressing selected dsRNAs protect roots from rootworm feeding damage. Here, we demonstrate that in-planta dsRNAs alone and in combination with Bt significantly effect multiple aspects of WCR life history while challenging these pests to a novel mode of action. Beyond root feeding protection, our results indicate that this approach may serve as an effective resistance management option as we move forward with additional options for managing rootworms of maize.

The effective control of European corn borer (ECB) is a very important aspect in food safety programmes in maize growing systems. Making holes in the stalks and in ears the pest larvae are a primary cause of maize infections by toxinogenic micromycetes dangerous both for human consumers and animals. The efficacy of selective insecticides (metoxyfenozide, indoxacarb), Bt maize and Trichogramma wasp (Tw) as preparation Trichocap ® against ECB was evaluated on several different locations during period 2002-2007. Before the harvest the plant injuries (tunnels and stalk breakage) caused by ECB were evaluated. The highest biological efficacy was achieved in Bt- maize (100%) in all experimental years. The effect of insecticide treatments was very good ranging from 80% to 95%. Tw applications resulted in satisfactory effect (cca 50%) in the most of years. The exception was previous season (2007) when the efficacy nearly 80% was observed. In addition, the concept of an antiresistant strategy in ECB control is proposed. In this concept Tw and selective insecticides can be applied in refugees used in insect resistant management in the protection against European corn borer. The work was funded by the project No 1B53043 of the Ministry of Agriculture of the Czech Republic.

The control of European corn borer (ECB) plays the most important in the prevention of mycotoxin accumulation in maize. Except of this, the occurrence of insecticide residues must be studied if chemical control used. Bt-maize, insecticides, and Trichogramma wasp were tested against ECB during period 2002-2007. To this purpose Bt-maize (‘MON 810’) and non-Bt hybrid (‘Monumental’) were used. The content of mycotoxins (NIV, DON, ADONs, T-2, HT-2, FUS-X and ZEA) in maize grain was evaluated. In addition, the incidence of insecticide residues (metoxyfenozide, indoxacarb) used in ECB chemical control of sweet maize was analysed. In Bt maize the lower occurence of toxinogenic micromycetes was observed. From the fungi linked to injuries by ECB to the most frequent species belonged: Fusarium subglutinans, F. verticillioides, F. proliferatum, F. sporotrichioides. Generally, the most frequent mycotoxin found in product was DON. NIV and ZEA appeared in some seasons only and the content of other mycotoxins was mostly bellow LOQ. A slight contamination by residues was observed in ear coats sampled during vegetation season. Before the harvest the metoxyfenozide residues was detected whereas indoxacarb declined better. Negligible contents (<MRL) of pesticide residues left by the tested insecticides were found in harvested sweet maize grain.