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PubMed2001

Symbiotic fungal endophytes control insect host-parasite interaction webs.

Symbiotic microorganisms that live intimately associated with terrestrial plants affect both the quantity and quality of resources, and thus the energy supply to consumer populations at higher levels in the food chain. Empirical evidence on resource limitation of food webs points to primary productivity as a major determinant of consumer abundance and trophic structure. Prey quality plays a critical role in community regulation. Plants infected by endophytic fungi are known to be chemically protected against herbivore consumption. However, the influence of this microbe-plant association on multi-trophic interactions remains largely unexplored. Here we present the effects of fungal endophytes on insect food webs that reflect limited energy transfer to consumers as a result of low plant quality, rather than low productivity. Herbivore-parasite webs on endophyte-free grasses show enhanced insect abundance at alternate trophic levels, higher rates of parasitism, and increased dominance by a few trophic links. These results mirror predicted effects of increased productivity on food-web dynamics. Thus 'hidden' microbial symbionts can have community-wide impacts on the pattern and strength of resource-consumer interactions.

Animals↗
PubMed1996

Insect Control and Dosage Effects in Transgenic Canola Containing a Synthetic Bacillus thuringiensis cryIAc Gene.

Zygotic hypocotyls of canola (Brassica napus L.) cv Oscar, cv Westar, and the breeding line UGA188-20B were transformed with a truncated synthetic Bacillus thuringiensis insecticidal crystal protein gene (Bt cryIAc) under the control of the cauliflower mosaic virus 35S promoter using Agrobacterium tumefaciens-mediated transformation. Fifty-seven independently transformed lines were produced, containing 1 to 12 copies of the transgenes. A range of cry expressors was produced from 0 to 0.4% Cry as a percentage of total extractable protein. The Brassica specialists, the diamondback month (Plutella xylostella L.) and the cabbage looper (Trichoplusia ni Hubner), were completely controlled by low-, medium-, and high-expressing lines. Whereas control of the generalist lepidopteran, the corn earworm (Helicoverpa zea Boddie), was nearly complete, the other generalist caterpillar tested, the beet armyworm (Spodoptera exigua Hubner), showed a dose response that had a negative association between defoliation and cry expression. These plants were produced as models for an ecological research assessment of the risk involved in the field release of naturalized transgenic plants harboring a gene (Bt) that confers higher relative fitness under herbivore-feeding pressure.

Journal Article↗
PubMed1982

Effects of xanthene dyes in cattle diets for insect control: diet digestibility and fecal excretion.

The effects of rose bengal, erythrosin B and fluorescein on ruminant digestion were evaluated by an in vitro rumen technique. Rose bengal reduced in vitro dry matter disappearance (IVDMD) values starting at .5 mM in the nutrient media and erythrosin B reduced IVDMD values starting at .05 mM in the nutrient media. Maximum reduction in IVDMD values was observed at 3.0 mM of rose bengal and erythrosin B. Fluorescein depressed digestion but not as severely as rose bengal or erythrosin B. Dry matter digestibility (DMD) values for steers given erythrosin B at a daily dosage of 6.5 mg/kg body weight were higher (P less than .05) than DMD values for control steers. DMD values were higher for steers given 16.3 or 26.1 mg erythrosin B/kg body weight daily than for the control steers, but the differences were not significant. There were no significant differences among animals given the different dosages in digestible energy. Recovery of erythrosin B from feces of treated steers varied with time, indicating that steers fed erythrosin B at a dosage of 6.5 mg/kg body weight might excrete feces during some periods of the day which would not control face fly development; however, administration of erythrosin B at a dosage of 16.3 mg/kg body weight would provide enough erythrosin B in feces to control face fly development throughout a 24-h period.

Animals↗