Summary 1.While great effort has been made in documenting the processes that drive plant-induced susceptibility after herbivore attack and it is widely accepted that herbivores can facilitate plant diseases, the relative importance of this interaction in controlling plant growth in natural systems remains largely unexplored. 2. In south-western Atlantic salt marshes, we investigated the importance of disease after herbivory by examining: (i) whether or not a herbivorous crab facilitates disease (i.e. fungus infection) in marsh plants ( Spartina alterniflora and S. densiflora ) when clipping off small portions of leaves and (ii) the separate and interactive effects of crab grazing but fungal infection in controlling marsh plant growth. 3. Our results show that crab grazing facilitates fungal infection in Spartina leaves. A factorial field experiment shows that both direct crab herbivory and fungal infection strongly suppress plant production (by more than 50%). 4. Synthesis . These experimental results demonstrate that fungal infection following herbivory attack can decrease salt marsh plant production and that increased disease susceptibility can be a fundamental factor in controlling plant production in natural ecosystems, even in cases where herbivores do not directly inoculate the pathogen but only damage plant tissue.

A search for bioactive compounds, inhibitors of Paenibacillus larvae, the causal agent of American foulbrood, a honeybees' disease, was carried on. Extracts of two fungal strains, Alternaria brassicicola and Alternaria raphani, isolated from pollen collected from beehives, exhibited a specific inhibitory activity against this bacterium. From these extracts and by means of chromatographic steps and bioassay-guided fractionation, three tetramic acids were isolated. The compounds were identified by spectroscopic methods and the absolute stereochemistry was chemically determined. L-Tenuazonic acid was shown to be responsible for the antibiotic activity. This compound showed a MIC of 32 lg/ml, comparable with that of oxytetracycline, an antibiotic currently used for the prevention of American foulbrood.q Dedicated to the memory of Dra Alicia M. Seldes.

A new tetrapeptide D-Phe-L-Val-D-Val-L-Tyr (1), along with three known diketopiperazines and pseurotin A, were isolated from the culture of Penicillium canescens, collected from pollen from beehives, in a screening for new antimicrobial products from unexplored sources. The structure of the tetrapeptide, which exhibits antifungal activity comparable with that of the commercial product benomyl against the soybean phytopathogen Fusarium virguliforme, was determined by spectroscopic (2D-NMR, and MS and MS/MS) and chemical methods, and the sequence was confirmed by comparison with authentic synthetic isomeric peptides.

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Chalkbrood is a fungal disease of honeybees (Apis mellifera L., Hymenoptera:Apidae) caused by Ascosphaera apis Maassen ex Claussen (Olive et Spiltoir). Ascosphaera apis is a heterothallic fungus that affects larvae of the honeybee. Diseased brood becomes mummified and mummies are white, gray, or black depending on the predominance of the sexual stage of the fungus. If spore-cysts are formed as a result of mating, infected larvae become gray or black in color. Larvae infected only by mycelia, without spore-cysts, are white (Gilliam et al., 1988;Gilliam and Lorenz, 1993).Larvae ingest the fungal spores when they are fed by adult bees that carry the spores. AbstractInoculation of Apis mellifera colonies with chalkbrood is a good way to test for hygienic behavior. The use of compatible pure strains of Ascosphaera apis, the causative agent of chalkbrood, could maintain homogeneity among experiments. Mycelium aging, viability, purity and capacity to produce spore-cysts were evaluated in MY20 and integral rice kernels (IRK) medium. Ascosphaera apis strains on MY20 developed aging symptoms by the 30 th day and developed pure colonies until the 77 th day. The same strains on IRK showed aging symptoms by the 30 th day of growing, but they produced pure colonies for 360 days. Spore-cysts obtained from pure strains preserved in IRK and spore-cysts from wild black mummies obtained from honeybee hives were used to inoculate fifth instar A. mellifera larvae. Ascospores from black wild mummies or spore-cysts obtained from pure strains preserved in IRK were equally effective in causing clinical symptoms of the disease, which has main advantages: permanent inoculum availability and genetic homogeneity.Additional key words: Apis mellifera, chalkbrood, culture media, honey bees, hygienic behavior, larvae inoculation, preservation. ResumenComunicación corta. Viabilidad y patogenicidad de Ascosphaera apis preservado en cultivos de arroz integral