no abstract provided by author / Master of Science

In this thesis chromatographic conditions for the HPLC analysis of ribonucleotides AMP, ADP and ATP were optimized. For their separation chromatographic column, Nucleogel SAX 1000-8, 50 x 4,6 mm, from the German company Marcherey-Nagel was used. The mobile phase of a 0,2 mol/L solution of KH2PO4, its pH was adjusted with 1mol/L with potassium hydroxide to pH = 5,00. As the most suitable flow rate was selected 1,0 mL/min. The analysis was conducted using an isocratic elution. Detection was conducted by a DAD detector at a wavelength of λ = 260 nm. Substances were eluted in the following order AMP (tr = 0,911 min), ADP (tr = 1,667 min) and ATP (tr = 7,262 min). The total analysis time of the mixture of standards, under the conditions mentioned above, lasted for 10 minutes. For the extraction of adenosine-5-ribonucloetides the real matrix frozen and lyophilized leaves of tobacco virginia (Nicotiana tabacum L.) have been used. Two methods of extraction were applied. The first procedure was based on the extraction of AMP, ADP and ATP from the leaves of the tobacco plant by boiling deionized water. In the second method 0,07 mol/L HClO4 for the extraction instead of deionized water was used. Keywords: HPLC, adenosine ribonucleotides, AMP, ADP, ATP, tobacco virginia

The effects of indigenous predators on green peach aphid (GPA), Myzus persicae (Sulzer), populations on flue-cured tobacco were evaluated in 1985 and 1986. The most common GPA predators found on tobacco were convergent lady beetle (CLB) (Hippodamia convergens), syrphid flies, Geocoris spp., Jalysus wackhimi, Nabis spp., Chrysopa spp., Micromus sp., and several other species coccinellids. However, CLB was the only predator that had a numerical response to increasing GPA density on tobacco. In the laboratory, the minimum number of GPA required to initiate reproduction in CLB, and the conversion rates were two factors that determined the oviposition rate of CLB. In fields, CLB demonstrated a sigmoid curve predator-prey relationship. CLB did not show a linear relationship until GPA populations reached a certain density. Furthermore, CLB did not show a response when GPA density was above the satiation point. Although CLB were able to reduce GPA population growth, they were not able to maintain GPA populations below the economic injury level. Two factors probably limited the success of CLB to control GPA populations on flue-cured tobacco: 1.) the glandular trichomes of tobacco which produced gummy exudates, and 2.) the satiation point of CLB when GPA populations were very high. In addition, interplanting tobacco with clover increased the number of syrphid fly larvae on tobacco. Likewise, tobacco interplanted with sunflowers had increased big-eyed bug, populations, and tobacco-alfalfa and tobacco-tobacco plots had higher stilt bug populations on tobacco. / Master of Science

The temperature-dependent development of red and green morphs of the green peach aphid, Myzus persicae (Sulzer), was compared on flue-cured tobacco, Nicotiana tabacum (L.), at moderate to high constant temperatures in the laboratory. The red morph was found to develop faster and reproduce more than the green morph at temperatures that promoted the most rapid population growth of either morph. In addition, mean longevity of the green morph was increasingly and significantly shorter than the red morph as temperature increased above the mutual optimum temperature (25 °C) for population increase. Study of the growth of GPA populations on commercial flue-cured tobacco farms in Virginia indicated the initial GPA population is highly aggregated. As the population increases, it becomes increasingly more randomly dispersed within the field. The typical pattern of temporal development of GPA was a bimodal distribution with the greater proportion of individuals occurring after topping of the crop. Cumulative proportional population growth models using degree-days were able to adequately describe growth of populations only on individual farms. Study of the within-plant distribution of GPA found that populations developed colonies of greatest intensity on the youngest leaves. The proportion of the total GPA population found on each leaf occurring on the lower leaf surface decreased with ascending leaf position. In addition, the proportion of the total plant population found on the lower leaves was highest as the crop approached the topping stage. / M.S.