The life history, temperature, humidity, and feeding requirements of the phytoseiid predator mite, Typhlodromus americanus Chant and Yoshida-Shaul were tested in the laboratory. Occurance of the mite in the field during different times of the year was investigated as well. Effects of temperature and humidity on egg hatch, the feeding requirements of the larvae, the amount consumed by each life stage, the length of each life stage and suitability of different food sources were investigated in the laboratory. The use of the mite as a biological control agent was evaluated by using the information gained from the laboratory experiments. T. americanus was originally discovered in plantation grown Douglas-fir in western Oregon. Since that time the mite has been found on a number of other hosts throughout North America. The mite is active year round in the Christmas tree plantations of the Willamette Valley in Oregon. The adult is found in or near the one year old bud scars and the eggs are typically deposited there also. Life parameters were measured providing a net reproductive rate of 4.23, a mean generation time of 24.45 days, and an intrinsic rate of increase of 0.059 The intrinsic rate of increase was low when compared to other predator mites and numerical response to prey increase would not be possible with such a low rate. The optimal temperature for the shortest eclosion time (54.4 hr.) and the highest survival (96.4%) was 26��C. The regression of temperature vs. time to hatch gave a 90% R�� with both the slope and intercept significantly different from zero. Humidities above 70% had survival rates over 96% and eclosion rates in the range of 50-58 hours. The relative humidity at which 50% of the population died was 58.6%. The mite was found to feed readily on the pest mite Oligonychus ununguis (spruce spider mite), as well as Tetranychus urticae (two spotted spider mite), and corn, oak, and Douglas-fir pollens. The larval form of the predator mite does not require food to molt to the protonymph, but the protonymph does require food to molt. If water is provided the entire time from egg to death, the protonymph can survive about ten days. Females consumed more Tet. urticae than males in both the immature and adult stages. The T. americanus that were fed corn pollen and Tet. urticae (complete diet) lived for over 115 days. Mites raised on oak and corn pollens did not survive as long (only 70-80 days), and those raised on Douglas-fir pollens did not reach adulthood. Egg production was observed on the complete diet, but not on the diets of pollen. The largest number of eggs were laid around the twelfth day after the molt to adult. Control and management of field conditions to improve habitat for T. americanus will be the best approach for its use as a biological control agent. As it does not respond numerically to prey increase, it will be more effective in a regulatory role to prevent these increases while the prey is at low levels. / Graduation date: 1996

Hippodamia convergens Guerin-Meneville was selected for rapid development through five generations at four constant temperatures (18, 22, 26, and 30��C). Two levels of selection were used: intense and moderate. Differences in developmental rate, survivorship, live adult weight, aphid consumption, adult longevity, and fecundity were measured for both groups and an unselected line. The two selected lines exhibited significant differences in developmental rate after the first generation of selection. The differences increased by the fifth generation of selection. Average differences between selected lines at 18, 22, 26, and 30��C in development from egg to adult were 4.9, 3.0, 1.0, and 1.5 days, respectively. Individuals from the intense selected line had a lower developmental threshold (11.3��C) than the moderate selected line (12.0��C). Also, degree-day requirements from egg to adult were lower in the intense (266 DD��) than moderate (277 DD��) line. Wild type beetles accumulated 231 degree-days above a threshold of 13.6��C. Survivorship at cold temperatures significantly increased with selection for fast development. In addition, no significant differences occurred in either live adult weight, total larval consumption of prey, fecundity, or adult longevity. Larvae selected for fast growth consumed higher numbers of aphids per day and were more efficient metabolically in converting prey mass into body mass than slow growing larvae. Because of a lower developmental threshold and lower degree-day requirements, for complete development, beetles from the intense selected line may accumulate more degree-days throughout a year compared to a moderate selected line. Predictions of population growth, based on an equation for intrinsic growth rate, showed that beetles from the intense selected line would produce 1.6 and 1.4 times more individuals in a 60-day period than beetles from the moderate selected and unselected lines, respectively. The results suggest that intense selected beetles would develop faster earlier in the season and would produce higher population numbers under optimum conditions. Thus, selection of H. convergens produced superior beetles for future introductions in biological control. / Graduation date: 1995

Bertha armyworm, Mamestra configurata (Lepidoptera: Noctuidae), is an important pest of cruciferous oilseed crops in western Canada. A nuclear polyhedrosis virus, MacoNPV, isolated from M. configurata, has demonstrated as high as 95% infection in field populations of bertha armyworm. MacoNPV isolates from different geographic areas differ in terms of their virulence to bertha armyworm. Restriction endonuclease (REN) fragment analyses show that all of the geographic isolates are closely related viruses but with some distinct REN pattern differences. Most of these geographic isolates are heterogenous mixtures of genotypes. The thesis describes the cloning and physical mapping of the 156.9 kbp genome of the MacoNPV-90/2 geographic isolate, including 112 restriction sites for six common REN, BamHI, EcoRI, HindIII, PstI, SmaI and XhoI. Twenty plaque purified strains of MacoNPV were isolated in a cultured Mamestra brassicae (Mbr) insect cell line. The EcoRI restriction patterns of these pick plaque (pp) strains fell into 10 different categories. In order to investigate the difference among these pp strains, and between these strains and the parental geographic isolates in terms of REN patterns, virulence to insect hosts, and their growth rates in insect cell lines, some of these isolates were selected for bioassays in bertha armyworm larvae and in the Mbr cell line.

Presently, most bacterial diseases of eel (Anguilla japonica) are controlled by antibiotics. However, antibiotics not only kill the bacterial pathogens but also kill those bacteria which might be beneficial to eels. In the meantime, application of antibiotics may result in spreading and accumulation of the resistance genes which may in turn lower the efficacy the antibiotics in the future and may threat public health. The recent trend to such problems is to screen non-pathogenic bacteria which are competitive to the pathogenic bacteria in the same environments. The eel pathogen, Edwardsiella tarda, was chosen as the target in this study. Bacterial strains were isolated from different eel ponds and tested for the ability to inhibit the growth of E. tarda. Of 2,412 strains tested, eight of them showed the inhibition capability. The molecular weights of the bioactive ingredients are all smaller than 12,000 daltons indicating they are not protein in nature. One of the strains is Bacillus cereus, four of the strains are Bacillus sphaericus, two of the strains are Bacillus laterosporus, and one of the strains of identified as Pseudomonas areuginosa competed extremely well with E. tarda. These antagonistic bacteria may have the potential of becoming as bio-control agents.Tiger shrimp (Penaeus monodon) is an important agricultural product in Taiwan. The over all production peaked in 1988, since then the outbreak of viral infection has caused the shrimp aquaculture a heavy damage. The current production is merely 1/10 of the peak. Many solutions were proposed to solve the problem, such as: increase the immunity of the shrimp, study pumping of the underground water has caused serious land subsidence in the coastal areas. Therefore, conservation of water is the trend of current aquaculture. In this study, culturable bacteria were isolated from a closed tiger shrimp pond. The taxonomy of the bacteria was based on 16S rDNA sequence phylogeny. Roughly 8 groups (genera) of bacteria were identified, including: Vibrio, Pseudoalteromonas, Porphyrobacter, Flavobacterium, Rhodthermus and three uncertain genera.

This study addressed the possibility of rice blast fungus (Magnaporthe grisea) as a potential bioherbicide for the control of crabgrass (Digitaria sanguinalis), in turf/lawn plantings. Experiments were: (i) evaluation of the effect of bioherbicide inoculum dosage (titer) on disease severity in crabgrass; (ii) competition between crabgrass and tall fescue (Festuca arundinacea Schreb. 'Fawn') and the additive effect of rice blast bioherbicide on the competitiveness of crabgrass; (iii) survival of rice blast spores under non-conducive infection conditions on crabgrass; and (iv) effect of multiple inoculations of rice blast fungus and subsequent disease on crabgrass.Spore concentrations of 5 x 105 to 1 x 106 conidia/mI had no significant difference in effect on mean biomass reduction of treated crabgrass. All produced tissue death and loss of vigor in treated crabgrass, but no plant death. In one trial, a spore concentration of 2 x 106 conidia/ml produced 100% biomass loss in treated crabgrass.Competition studies indicated crabgrass will out-compete fescue 'Fawn' in plots of equal numbers of each plant, i.e., 3 fescue and 3 crabgrass. In 10 x 10 cm mini-lawns of fescue interspersed with 5 crabgrass plants, fescue will out-compete the crabgrass. In mini-lawns of fescue and crabgrass, infection of crabgrass with non-lethal doses of rice blast fungus improved fescue's ability to out-compete crabgrass. Three methods of investigating competition were tested. Mini-lawns sown with 0.5 g fescue seed (approx. 200 seeds) with crabgrass seed sown into centers of the four quadrants and in center of the mini-lawn, worked best.Survival of Magnaporthe grisea conidia under non-conducive conditions was tested by drying inoculated crabgrass seedlings for 0-48 hours prior to dew-deposition. Treatments verified spores remain viable at least 24 hours on crabgrass leaves under greenhouse conditions (25-40° C and 25-75% relative humidity).Two successive inoculations (at 3 days and 7 days after primary inoculation) of crabgrass with M. grisea conidia (5 x 105 conidia/ml) resulted in significant reduction in growth compared to a single spore application.Results suggested Magnaporthe grisea exhibits potential for future development as a commercial bioherbicide to control crabgrass (Digitaria sanquinalis). Current studies investigated integration in lawn grass, but should be applicable to situations anywhere crabgrass is considered a weed e.g., in corn (Zea mans) or soybeans (Glycine max). / Department of Biology