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.)

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.

No description available.

The effect of spore titer, virulency, and carrier systems on biological control of giant foxtail (Setaria faberi hermm.) with a species of Phoma isolated from this weed wereinvestigated. The lowest concentration of Phoma conidia which significantly affected (lowered) growth of giant foxtail was 1x106 conidia/ml. In conducting Koch's postulates, all but one (FF2) of the Phoma, isolates tested infected giant foxtail. Isolates FF1 and FF9 were the most virulent against giant foxtail. No correlation was apparent between virulency and fungus germination rate. No visible difference occurred with in vitro germination rates of spores incubated upon pea vsr water agar media; nutrient rich vs. nutrient poor media, respectively. These results suggest that Phoma spores already contain sufficient nutrients required for infection of foxtail. A definitive answer as to the effect of carrier system (e.g. surfactant, sticker, spreader, etc.) on efficacy of Phoma to infect foxtail could not be determined from results obtained, based upon statistical analysis of variance (ANOVA) for the single experiment performed. Several of the surfactant treatments (e.g. Silwet 77 and 408) did produce significant biomass losses against foxtail due to the phytotoxicity of the carrier system alone, and not reflective of fungal (Phoma) infection. Inoculation of foxtail plants with a conidial suspension amended with carriers of either Tween 20 (0.05%-0.1%) or methylcellulose (0.1%) should optimize chances for sufficient infection resulting in biological control of this weed. / Department of Biology

Inoculation studies were conducted in controlled environments with isolates of a Phoma sue. collected from leaf spot lesions on the weed giant foxtail. Limited host specificity studies resulted in this potential bioherbicide fungus killing all three foxtail species tested including Setaria faberi (giant), a. viridis (green) and S. lutescens (yellow). Several agronomically important plant species tested exhibited a hypersensitive-type response to infection, but these plants soon grew out of this symptom and appeared healthy. This bioherbicide preferred cool temperatures, exhibiting optimal biomass loss (100%) or death against foxtail seedlings following 120 hours leaf wetness with plants incubated at 20°C. At more conducive growth temperatures for the weed (25'C-300C), optimum biomass loss achieved was only 70% following 50 hours leaf wetness. Susceptibility to this Phoma sue. greatly decreased as foxtail seedlings attained 4 or more leaves per plant. To kill this weed, the author recommends inoculation of foxtail seedlings in early evening to take advantage of cooler temperatures and to inoculate plants between cotyledon to 3-leaf stages of growth. / Department of Biology

The production of Jersey Royal potatoes is an important industry for the island of Jersey. The crop is grown annually, and sometimes biannually, so there is no opportunity to practise crop rotation in order to control potato cyst nematodes (PCN), Globodera pallida and G. rostochiensis. Control of these pests in Jersey has traditionally relied on the use of nematicides, but with increased public pressure to reduce the use of pesticides and the intention of the Government of Jersey to eventually ban them, there is a desire for an alternative methods of control to be developed. Three nematophagous fungi, Plectosphaerella cucumerina, Paecilomyces lilacinus and Verticillium chZamydosporium, were isolated from PCN cysts taken from potato fields in Jersey. The efficacy of these fungi for the control of PCN was studied to determine their suitability for use in an integrated pest management programme. The radial growth rates of the nematophagolls fungi were reduced when grown on media amended with the fungicides Gambit and Rizolex, commonly used for the control of Rhizoctonia solani, another major pathogen of potatoes. Radial growth of V. chlamydosporium was also inhibited by Monceren and the nematicide Vydate. Growth of R. solani was inhibited by P. lilacinus at 20°C and 10°C in vitro and by V. chlamydosporium at 20°C, but the strain of V. chlamydosporiurn used did not grow at 10°c. Plectosphaerella cucumerina was a poor saprophytic competitor when grown against R. solani, P. lilacinus and V. chlamydosporium, therefore it may not be a suitable soil applied agent as it is out grown by other fungi in the soil. Paecilomyces lilacinus in a pelleted support matrix made from an alginate, gave better control of R. solani than non-formulated P. lilacinus alone. Of the different formulations of nematophagous fungi tested in pots, P. lilacinus incorporated into alginate pellets reduced the numbers of peN by the most (79.5%) and when applied in a field trial, reduced PCN population increase by approximately 60%. Plectosphaerella cucumerina, when incorporated into alginate pellets, also reduced field population increase by approximately 60%. A combination of these two formulated fungi tested in a plunge trial gave a poorer level of control than the fungi added individually. The fungi remained viable in alginate pellets for at least 18 months. The population composition of PCN in Jersey was previously unknown. Using an ELISA technique, this study has shown both PCN species are present, but the proportions were not determined. To ascertain whether the early lifting of Jersey potatoes was selectively reducing levels of one of the species of PCN, DNA was extracted from nematodes stained in situ in the roots of potatoes. The results were inconclusive and further work is required.