Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references (leaves 75-84). Also available on the Internet.

No description available.

No description available.

The ability of Nabis alternatus Parshley to reduce tobacco budworm, Heliothis virescens (F.), populations was studied in the laboratory, greenhouse and field. Tests were conducted at different temperatures and with different larval instars of tobacco budworm to determine their effects on predatory efficiency. Both immature and adult N. alternatus consumed more first-instars than of either second- or third-instars, or of the egg stage. Temperature significantly affected the predatory capability of N. alternatus. All instars and the adult exhibited a higher rate of consumption at 30°C than at temperatures of 20, 25 and 35°C; adults consumed more tobacco budworm larvae and eggs at all temperatures than did any of the nymphal instars. There were no differences in survival of the different N. alternatus stages at the different temperatures but the average number of days required to complete each instar was affected. Each increase in the predator-to-prey ratio resulted in a reduced survival of the tobacco budworm population. Release rates of 2500, 3750 and 5000 adults per acre resulted in mortalities of 55, 77, and 87%, respectively. Both adult and third-instar N. alternatus exhibited the higher searching and consumptive capacities at different ratios of first-, second-, and third-instar tobacco budworm infestations. All N. alternatus fed more at the 1:4 (predator/prey) ratio than at ratios of 1:1, 1:2, or 1:3. Longevity of adult N. alternatus varied when provided with food substances of sugar solution, green bean, no food or cotton plants at the different temperatures. Survival was greatest when provided with sugar solution over any of the other substrates, and when held at cooler temperatures. Compatibility of N. alternatus with other controls was studied under both laboratory and field conditions. Average longevity in combination with treatments of Elcarᴿ, Bacillus thuringiensis, or fenvalerate was 6.7, 5.9, and 1.3 days, respectively. Compatibility with the biological insecticides was very good and the combinations reduced first-instar tobacco budworm infestations more than did either alone.

No description available.

The GRASS (V. 4.0) geographical information system (GIS) was used to test the hypothesis that pheromone trap based predictions of Helicoverpa zea (Boddie) damage in processed sweet corn could be improved by considering spatial patterns of corn plantings and wind blocking features around the trap. Wind blocking features include: tree rows, wooded areas, large buildings close to the trap, and abrupt hillsides. Pheromone traps were monitored at 29 and 30 sites in 1990 and 1991. Corn development through the year and damage levels at harvest (percent infestation) were also recorded for these locations. Maps of all corn plantings and wind blocking features within 2.5 kilometers of the trap were created, digitized, and entered into the GIS for each site. A stepwise regression analysis considering 18 spatial and two non-spatial variables resulted in a highly significant (P<0.001) four variable regression model with an R�� of 0.82. Spatial input variables used in this model included the total number of hectares of corn within 2.0 kilometers of the trap as well as the average distance to wind blocking features on the north side of the trap. The non-spatial variables used were cumulative trap catch and date of first silk. A dynamic simulation model was also created. This was designed to filter from the trap catch those moths coming from plantings outside of the trapped planting. This model functioned by creating map surfaces in the GIS showing for each day the relative contribution to catch for each location around the trap. This map surface was the product for each location of relative moth population levels and the likeliness that a moth positioned there would be captured by the trap. The modified cumulative trap catch was expected to correlate more strongly to damage levels than the unmodified trap catch, but no run of the model produced a significant improvement in the correlation. In the process of collecting data for this project, circumstantial evidence was obtained which indicated that high synchrony between valley-wide moth catch levels and valley-wide timings of silking in corn could be used as an indicator of high damage years. / Graduation date: 1994

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 78-86). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 78-86). Also available on the Internet.

Efficacy of Bacillus thuringiensis Berliner against the first three larval instars of Heliothis virescens (F.) was studied under greenhouse and field conditions. The primary objective of these studies was to determine the susceptibility of the tobacco budworm to Dipel, a commercial preparation of Bacillus thuringiensis. Both greenhouse and field studies showed that first-instar larvae were more susceptible to all dosage levels of Dipel tested (0.125, 0.25, 0.5, and 1.0 1b/A). The higher rates of 0.5 and 1.0 1b/A gave better control and remained effective for longer periods against the first-, second- and third-larval instars than did the lower rates of 0.125 and 0.25 1b/A. The efficacy of all Dipel rates decreased significantly with each subsequent post-application-date bioassay, and only the higher dosages of 0.5 and 1.0 1b/A remained effective at the three-day residue period in the field studies. The addition of a feeding stimulant, Coax, at 0.25 1b/A, to all Dipel treatments resulted in a significant increase in larval mortality of all instars tested. Dipel plus Coax exhibited longer residual activity than did Dipel alone, indicating that Coax may protect the spores and toxin from degradation by the direct sunlight. When second-instar tobacco budworm larvae were allowed to feed on Dipel-treated terminals for 6, 18 or 30 hours and then transferred to untreated diet, they showed a great capacity to recover from the effect of the toxin. However, as the Dipel rate or exposure time was increased, the ability of larvae to recover was decreased. Dipel did have an effect on the biological activity of treatment-surviving larvae. Larval and pupal development was delayed, pupal weight was decreased, and female fecundity was reduced. In all cases the changes were proportional with the Dipel rate and with the length of exposure. No apparent effect was shown relative to adult longevity or egg viability for those surviving Dipel treatments as larvae. When Dipel was applied directly on tobacco budworm eggs, it had no effect on egg hatch but did significantly affect survival of newly-emerged larvae, indicating the larvae consumed a lethal dose of the toxin during eclosion. The compatibility of Dipel in combination with Geocoris punctipes (Say) against first-instar larvae of Heliothis virescens was also studied under greenhouse and field conditions. Results of these studies indicated the possibility of utilizing the two biological agents to suppress tobacco budworm populations in the field. A minimum density of one Geocoris nymph per 4 row feet is required, plus an effective field rate of Dipel. When adult tobacco budworms were fed on Dipel at 32000 IU/ml, their longevity and fecundity were significantly reduced. An adult feeding stimulant is needed to lure the adults to a Dipel source.

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves [224]-254). Also available on the Internet.