The carrot weevil, Listronotus oregonensis LeConte (Coleoptera: Curculionidae), is an important pest of carrot in northeastern North America. The objective of this study was to determine the host selection stimuli used by two L. oregonensis parasitoids: the adult parasitoid Microctonus hyperodae Loan and the egg parasitoid Anaphes victus Huber. / In the first chapter, the response of M. hyperodae females to various odor components from potential hosts and host plants was tested with a Y-olfactometer. / In the second chapter, the effect of L. oregonensis adult sex, feces and movement on host selection behavior of M. hyperodae females was evaluated by quantifying L. oregonensis adult movement and various M. hyperodae female behaviors in an arena. / In the third chapter, the response of A. victus females to different L. oregonensis related odor components was evaluated using a filter paper of which half was moistened with odor components and the other half with water.

In Quebec 11 840 kg of insecticides are used against the cabbage maggot, Delia radicum L. (Diptera: Anthomyiidae) each year. It is possible to decrease this quantity of insecticide by using natural enemies such as fungi, nematodes, predators and parasitoids. Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae) is a natural enemy of the cabbage maggot. Adults of this species are predators of eggs and larvae of cabbage maggot and the first instar larvae are ectoparasitoids of cabbage maggot pupae. A. bilineata oviposits its eggs in the soil, near plants infested with cabbage maggots. / Differences in size have been noted in the eggs of A. bilineata . In insects several factors can affect egg size. Certain females can oviposit small trophic eggs which serve as food for emerging larvae or egg size can be affected by factors such as size and age of female, as well as, food and host quality. These factors have been studied in A. bilineata in order to determine the conditions that favor the production of small eggs. (Abstract shortened by UMI.)

During a two years study (1993-1994) in southwestern Quebec, Artogeia rapae and Plutella xylostella were found to be the most important lepidopterous pests of cruciferous crops, followed by Trichoplusia ni and four minor species. The relationship between plant sampling and the use of degree-days, pheromone traps (P. xylostella) or butterflies counts (A. rapae) was assessed for A. rapae and P. xylostella. Three generations of A. rapae were observed annually, with a duration of 319.7 degree-days above $ rm 10 sp circ C (DD sb{10}),$ while P. xylostella had three to four generations with a duration of 277.7 $ rm DD sb{10}.$ Captures of P. xylostella were not linked to the level of infestations. By the end of summer, A. rapae was the most abundant species, especially on broccoli, while P. xylostella was often abundant early in the season. The complex of lepidopterous pests' natural enemies was identified, and the data were analyzed using an illustrated parasitoid web. Fourteen parasitoid and three hyperparasitoid species (12 Hymenoptera, 2 Diptera) were identified. The most important parasitoid, Cotesia rubecula, is a larval parasitoid of A. rapae that is newly established in Quebec. Overall, parasitism of lepidopterous eggs is almost not existent, whereas parasitism and infection of larvae and pupae by pathogens are important, but not significant to reduce butterfly populations. In order to evaluate the potential of oophagous parasitoids, the parasitism of up to 42 species/strains of Trichogramma was studied with different development stages of P. xylostella, A. rapae and T. ni eggs. Generally, Trichogramma females attacked preferably young eggs of a given host species. Females modified the number of offspring according to host size and host age, as fewer offspring emerged from the smallest or the oldest hosts. Host age had no impact on sex allocation. (Abstract shortened by UMI.)

Rhizoctonia solani (AG-3), the causal agent of Rhizoctonia disease of potato, overwinters as sclerotia on potato tubers. To develop a biocontrol strategy based on the prevention of the sclerotial germination, an isolation of microorganisms colonizing sclerotia of infected potato tubers (cultivars Norland, Atlantic and Souris), was conducted. In vitro screening was used to select effective antagonistic fungi against Rhizoctonia solani. Fifty fungal isolates were selected in order to cover all identified genera and potato variety and examined for their ability to inhibit germination of sclerotia which were incubated with the test fungus for 14 days. Twenty-four (24) fungal isolates were retained based on their ability to reduce sclerotial viability by more than 50% as compared with 100% viability of untreated sclerotia. These 24 isolates were further examined for their ability to protect Table beet seedlings against the pathogen in greenhouse soils. Based on their ability to protect Table beet seedlings from Rhizoctonia infections and to increase the number of secondary roots and root length isolates, F2, F11, F132, F158, and F258 were screened and test their efficacy to increase beet seed germination in field soils. (Abstract shortened by UMI.)

The Labiatae is a large family that occurs worldwide and have species that are adapted to almost all habitats and altitudes. Plectranthus is in this family. Plectranthus species are beautiful South African shrubs. The genus Plectranthus belongs to subfamily Nepetoideae of tribe Ocimeae. The test microorganisms were chosen carefully as each one belonged to a different taxonomic group of fungi and bacteria. Biologically active mono- and sesquiterpenoids are frequently found in many species of Plectranthus but there are little published data that directly link the presence of specific compounds in a species with the traditional uses of that species. Various Plectranthus spp. were collected and dried, followed by chemical extraction using various solvents. Dichloromethane extracts of P. fruticosus and P. ecklonii were screened for antibacterial and antifungal activities using the agar well and trench diffusion methods. It was found that both methods produced inconsistent results. The trench method required a bigger volume of plant extract to be filled into the well, hence, better biological activity was observed with that method. The well method required a smaller volume therefore poor activity was noted with this assay. The size of inhibition zones are dosage dependent. Overall, both plant extracts exhibited antibacterial but no antifungal properties. The pure compound (1), 11-Hydroxy-2-(4-hydroxybenzoyl)-5,7,9(11),13-abietatetraen-12-one, isolated from P. ecklonii was found to be the same as compound (10) which was isolated from P. lucidus. P. hadiensis was extracted using dichloromethane and hexane. The dichloromethane extract proved to contain much higher biological activity than the hexane extract. Three pure compounds, identified as diterpenes, were isolated from the crude dichloromethane extract of P. hadiensis. 6,7-Dihydroxyroyleanone-6,7,12-trihydroxy-8,12-abietadiene-ll,14-dione (2) and 7(alpha)-formoxy-6(beta)-hydroxyroyleanone (3) exhibited good antibacterial and antifungal activity but not against all the test organisms. The remaining pure compound, 7(alpha)-acetoxy-6(beta)hydroxyroyleanone (4), exerted good antifungal activity. This was measured by the inhibition zone which measured up to 14mm when compound 4 was tested against S. sclerotiorum. When testing the hexane extract against the Bacillus formulations, the pellets that were suspended once in Ringer's solution produced bigger inhibition zones than the pellets that were suspended twice. This could be due to bacterial cells washing out of the suspension. The dichloromethane extract of P. praetermissus proved to be very active against X campestris, producing an inhibition zone of 8 - 20mm. Two pure compounds were isolated from the crude extract and identified as diterpenes. Compound 5, 20(10--> 5)-abeo1( 10),6,8,11,13-abietapentaene-11,12,16-triol, and compound 6, 11,12,15-trihydroxy-20( 10-->5)-abeo-abieta-1-(10),6,8,11,13-pentaene are both known compounds which have previously been isolated from Salvia apiana. P. cilatus was extracted with chloroform and tested against various microorganisms for antifungal and antibacterial activities. It showed poor biological activity overall, except against S. sclerotiorum. The crude dichloromethane extract of P. zuluensis exhibited good antibacterial activity, which was limited to the Gram negative test organism. The extract produced an inhibition zone of 10-12mm when tested against X campestris. Pure compound 7, 2-hydroxy-4,6dimethoxyacetophenone, exerted excellent inhibition against B. subtilis and S. sclerotiorum. Neither compound 8, 1,2,4-trimethoxy-5-(2-propenyl)-benzene, nor compound 7, inhibited Candida spp., F. oxysporum and R. solani. Two diterpenes were isolated from the aerial plant parts of P. lucidus with dichloromethane and their structures elucidated by spectroscopic means. The pure compound 9, 11-hydroxy19-( 3-methyl-2-butenoyl)-5,7,9(11), 13-abietatetraen-12-one, showed moderate antifungal activity whereas compound 10, 11-hydroxy-2-(4-hroxybenzoyl)-5,7,9(11),13-abietatetraen12- one, showed high antifungal activity against R. solani, S. sclerotiorum and F. oxysporum. The crude and the pure compounds (formerly isolated from P. parviflorus) showed inhibition against X campestris. The dichloromethane extracts of P. purpuratus subsp. purpuratus and P. purpuratus subsp. tongaensis exhibit similar levels of biological activity when tested against the same test organisms. Poor antibacterial activity was noted with both extracts. However, excellent antifungal activity was depicted when both plant extracts were tested against F. oxysporum, R. solani and S. sclerotiorum. However, the highest biological activity was noted by R. solani which was totally inhibited by both dichloromethane extracts. The pure compound (11) isolated from P. purpuratus subsp. purpuratus was found to have the same chemical structure as compound (9) previously isolated from P. lucidus. The bioautography assay was used to detect and activity-guide the fractionation of antimicrobial compounds from all the Plectranthus spp. tested. The TLC fingerprint showed a zone of clearing around the lower bands of P. fruticosus and P. ecklonii when the plate was sprayed with a suspension of B. subtilis. This result is consistent with the agar well diffusion method. Clear zones were also noted on some bands of the extracts of P. zuluensis, P. ciliatus, P. hadiensis and P. praetermussis. Clear zones indicate inhibition of growth. Other plant extracts tested for biological activity were from the family Lamiaceae, however, not of the genus Plectranthus. Persicaria senegalensis, Pycnostachys reticulata and Ficus sur possessed moderate biological activity overall. It is interesting to note that P. senegalensis and F. sur exert high biological activity against Candida spp. This could be useful as herbal remedies for yeast infections. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.

In 1992, a research program was initiated to select suitable antagonists against the saprophytic (or winter) phase of the apple scab pathogen, Venturia inaequalis. An improved method for the mass screening of a vast collection of fungi was developed for this purpose. Some of the previously reported criteria such as leaf rheology and overwintering structure production proved unreliable or fastidious and cannot be used for in vitro antagonist selection. The main antagonism selection criterium retained was the in vitro inhibition of ascospore formation. To measure ascospore production, a simplified method of in vitro pseudothecia production was devised. This new method eliminates the need for prior conidia production by using a mycelial suspension and greatly reduces the risks of sterile mating by using a cocktail of Venturia inaequalis strains of different origins. Finally, the production cycle duration was reduced by varying the incubation temperature during the simulated winter. Moreover, a quick and efficient method of ascospore collection was developed. Ascospores were forcibly ejected in a large scale bubbler type apparatus in only one hour. This bubbler can be used for other studies including axenically produced ascospores. This new method compared favourably to the previously reported method and was used to screen a collection of about forty-two fungi. Six proved to significantly reduce the ascospore production of Venturia inaequalis. Two were as effective as Athelia bombacina, a previously reported antagonist of pseudothecia formation and inhibited over 98% of the ascospore production. These new organisms are now available for future field tests. Future selections from a large collection of saprophytes can now be based on a reliable and simple in vitro screening methodology.

Venturia inaequalis, the causal agent of apple scab, overwinters in apple leaves on the orchard floor. To develop a control strategy based on the prevention of the maturation of overwintering pseudothecia, a sampling of fungi colonizing dead apple leaves was conducted from different orchard floors in Quebec during the spring and fall of 1993. A total of 345 different isolates were obtained, from which fifteen genera have never been previously recorded as colonizers of apple leaves in North America. Small differences were detected in genera richness among orchards but the fungal composition of each orchard was fairly unique. Different tests on growth on amended media and leaf decomposition demonstrated that leaf degradation is not a reliable parameter alone to screen antagonist against V. inaequalis. No significant relation between growth on amended media, leaf rheology and ascospore inhibition was detected. However, 40 fungi reduced significantly ascospore production more than 87% compared to the control (V. inaequalis only). Of these antagonists, 30% decomposed apple leaves, suggesting that competition for the substrate is involved in the mode of action of at least one third of the antagonits detected. Other possible modes of antagonism are discussed.

Glucose was present in substantially greater concentrations in whole body extracts of fourth instar Aedes aegypti L. larvae than was trehalose; in contrast, trehalose was more abundant than glucose in haemolymph extracts. Preliminary studies suggested that infection of Ae. aegypti by the entomopathogenic digenean Plagiorchis elegans Rudolphi alters the carbohydrate metabolism of fourth instar larvae. Within 24 hours of cercarial penetration, total body extracts of infected fourth instar larvae exhibited decreased trehalase activity, increased trehalose-6-phosphatase activity, and an accumulation of trehalose in comparison to uninfected larvae. Concentrations of glucose, glycogen and lipids, and the activity of glycogen phosphorylase a were similar in extracts of infected and control larvae. The predominant fatty acids, in both control and infected larvae, were C 18:0, C 18:1 and C 18:3. There were no significant differences in the types and proportions of fatty acids found in control and infected larvae. Parasitic infection is discussed in terms of impaired trehalose metabolism.

Thirty-two isolates of rhizosphere bacteria, selected for their ability to inhibit zoospore germination and/or mycelial growth of Pythium aphanidermatum (Pa) in vitro, were evaluated in a test tube bioassay using cucumber c.v. 'Straight 8'. These isolates were identified as Psedudomonas corrugata (Pc13 or 35) and P. fluorescens (Pf15, 16 or 27). All but one of the five isolates effectively colonised the roots of cucumber plants in short term studies. Isolates 15 and 35 were found to maintain high population densities throughout the time period. Pa-inoculated plants treated with the Pc13 or Pf15 produced fruit yields equal to 92 and 74% respectively of the control (no Pa, no bacteria). Pa-inoculated plants without bacteria yielded only 46% of the control. In the fall crop, Pa-inoculated plants treated with Pc13 or Pf15 yielded 52 and 47% of the control compared to Pa-only treatment, which yielded 12.5% of the control. In both crops, treatment with any of the bacterial isolates resulted in significantly reduced cull rates compared to the Pa-only treatment.

The use of a biofungicide on the perfect stage of V. inaequalis on leaf litter is one potential way to reduce the number of fungicides used to control apple scab. The previous in vitro screenings of Quebec mycoflora have shown that several isolates are able to significantly reduce the primary inoculum of the pathogen. Among the screened fungi, P176A and P130A, reduced over 98% of the ascospore production and were as effective as Athelia bombacina. However, because in vitro tests are generally poor predictors of in vivo assays a re-evaluation of the antagonists was done under field conditions. Eight fungal isolates, leaf shredding, and two comparative treatments (A. bombacina, 5% urea) were applied to intact scabbed leaves in October 1994 and 1995. After the treatments, the leaves overwintered on the orchard ground until the next spring. In April, samples of treated leaves were randomly selected and placed in spore traps to collect the ejected ascospores during rainfall. Since the primary inoculum was ejected during a four-month period, antagonism was based upon ratings taken throughout the whole ejection season. To evaluate the effect of incubation conditions on the antagonistic performance we incubated separately, in vitro and in vivo, sterile leaf disks which were artificially inoculated with V. inaequalis and fungal isolates. (Abstract shortened by UMI.)