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Biomedical subjects

D W Ragsdale

Publications and source records attributed to D W Ragsdale.

5 recordsLinked to original sources
PubMed2004

Enumerative and binomial sequential sampling plans for soybean aphid (Homoptera: Aphididae) in soybean.

Since the discovery of the soybean aphid, Aphis glycines Matsumura, in midwestern U.S. soybean, Glycine max L., in 2000, the aphid has become a significant economic pest. Basic information about estimating population density within fields is unknown. Therefore, we developed two sampling plans to efficiently characterize A. glycines densities. Enumerative and binomial sequential plans were developed using 89 data sets collected from 10 commercial fields sampled during 2001-2003. Re-sampling software was used to validate the enumerative plan on whole plant counts, based on Taylor's power law parameters (a = 9.157 and b = 1.543). For research applications, the enumerative plan was modified to provide an actual precision level of 0.10 (SE/mean), which resulted in an average sample number of 310 individual plants. For integrated pest management (IPM) purposes, we developed an enumerative plan with an actual precision of 0.25, which resulted in an average sample number of 38 individual plants. For IPM applications, the binomial plan will likely be more practical. Binomial plans were developed using two tally thresholds at five action thresholds. Final analysis of the operating characteristic curve for each plan indicated that the tally threshold of > or = 40 aphids per plant, and an action threshold of 0.837 (84% of the plants infested) provided the most correct treat (4%) and no-treat (95%) decisions, with very low incorrect treat (0.5%) and no-treat (0.5%) decisions. A tally threshold of > or = 40 aphids per plant and action thresholds of 84% of plants infested is equivalent to a mean density of 250 aphids per plant, a recently recommended economic threshold. Using this threshold, the minimum required sample number for the binomial plan was 11 plants.

Agriculture↗
PubMed2004

Demography of soybean aphid (Homoptera: Aphididae) at summer temperatures.

Soybean aphid, Aphis glycines Matsumura, is now widely established in soybean, Glycine max L., production areas of the northern United States and southern Canada and is becoming an important economic pest. Temperature effect on soybean aphid fecundity and survivorship is not well understood. We determined the optimal temperature for soybean aphid growth and reproduction on soybean under controlled conditions. We constructed life tables for soybean aphid at 20, 25, 30, and 35 degrees C with a photoperiod of 16:8 (L:D) h. Population growth rates were greatest at 25 degrees C. As temperature increased, net fecundity, gross fecundity, generation time, and life expectancy decreased. The prereproductive period did not differ between 20 and 30 degrees C; however, at 30 degrees C aphids required more degree-days (base 8.6 degrees C) to develop. Nymphs exposed to 35 degrees C did not complete development, and all individuals died within 11 d. Reproductive periods were significantly different at all temperatures, with aphids reproducing longer and producing more progeny at 20 and 25 degrees C than at 30 or 35 degrees C. Using a modification of the nonlinear Logan model, we estimated upper and optimal developmental thresholds to be 34.9 and 27.8 degrees C, respectively. At 25 degrees C, aphid populations doubled in 1.5 d; at 20 and 30 degrees C, populations doubled in 1.9 d.

Animals↗
PubMed1998

Serum and skin surface antibodies and their associations with sheep biting lice, Bovicola ovis, on experimentally infested sheep.

The sheep biting louse (Bovicola ovis) feeds superficially on the skin of sheep but appears to stimulate an immune response. In this study we examined the association between louse infestation and serum and skin surface antibodies. Louse numbers were monitored on experimentally infested Polypay and Columbia ewes for two years and on their lambs in the second year. Serum and skin wash samples were tested for antibodies to soluble extracts of B. ovis, Stomoxys calcitrans and Musca autumnalis by enzyme linked immunosorbent assay (ELISA). In addition, the effects of skin wash extracts on B. ovis were examined in vitro. The titre of anti-B. ovis antibodies in the serum did not differ significantly between infested and naive ewes. However, there was an increase in serum antibody titre which coincided with periods of high louse density in ewes with high louse counts. Infested lambs had higher serum antibody levels than naive lambs. Substantial cross reactivity was evident among extracts of the different insects. Densities of lice on the ewes during population decline were negatively related to the titre of skin surface antibodies. Skin washings collected from sheep during B. ovis population decline reduced the number of louse progeny when incorporated into louse diet. These results indicate that B. ovis stimulates an immune response in sheep and suggest that compounds on the skin surface may play a role in the regulation of louse populations.

Animals↗
PubMed1980

Isolation of O1 serovars of Vibrio cholerae from water by serologically specific method.

Vibrio cholerae bacteria of the serological variety O1 were consistently isolated from water samples by passing the water with added Tween 20 through columns packed with polystyrene beads coated with antibodies against the O1 antigenic determinants. The beads from the columns were washed, transferred to alkaline peptone broth, and incubated. The O1 serovars were isolated and identified by established procedures.

Antigens, Bacterial↗