More wasps of Encarsia formosa Gahan (Hymenoptera: Aphelinidae) were found on fertilized poinsettias, Euphorbia pulcherrima (Willd.) (Euphorbiaceae), than on non‐fertilized plants. Parasitization of Bemisia argentifolii Bellows & Perring (Homoptera: Aleyrodidae) by E. formosa was higher on plants treated with calcium nitrate than with ammonium nitrate or on control plants. In a no‐choice test, host feeding by E. formosa was higher when hosts were on fertilized plants than when hosts were on control plants. The nitrogen content of whitefly pupae reared on plants treated with ammonium nitrate was higher than those on calcium nitrate‐treated plants.
Variability in the parasitization of B. argentifolii by E. formosa appears to be due to host plant‐mediated differences in the whiteflies. E. formosa may be influenced by the nutritional suitability of the host, which influences whether wasps continue to oviposit, feed, or disperse.
Breeding for resistance to Fusarium head blight {FHB; caused by Fusarium graminearum Schwabe [teleomorph Gibberella zeae (Schwein) Petch]} is complicated because there is no accurate method for quantifying the disease organism. Most breeders rely on visual scoring for FHB and deoxynivalenol (DON) analysis to assess disease severity, but both DON and visual scoring are subject to error. The objective of this study was to compare a Fusarium‐specific quantifiable enzyme‐linked immunosorbent assay (ELISA) to DON and visual assessment of FHB. A doubled‐haploid mapping population was grown in two environments and breeding lines in the North American Barley Scab Evaluation Nursery (NABSEN) were grown at four locations. Both experiments used a randomized complete block design and were analyzed for Fusarium by ELISA, DON, and visually scored for FHB. ELISA values for the doubled‐haploid lines were consistent over years, and lines that were low in ELISA were also low in DON. Broad sense heritability was greater for ELISA (0.48) than DON (0.19) or visual scores of disease (0.29) in the NABSEN study. Numbers of locations and replications necessary to screen for disease were calculated for ELISA, DON, and FHB. ELISA required one‐third to one‐fourth as many replications and locations as did DON or FHB. Temperature and osmotic potential had little effect on mycelial antigen used for ELISA in vitro, but both affected DON. ELISA is a practical alternative to combined visual scores and DON analysis for breeders interested in improving FHB resistance.
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