Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains xvi, 166 p.; also includes graphics (some col.). Includes bibliographical references. Available online via OhioLINK's ETD Center.

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Diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae) is a serious pest of crucifer vegetables (Brassica sp.) worldwide because of a lack of effective natural enemies in certain regions and because of insecticide resistance. In 2003, laboratory and field studies were initiated in Virginia to better understand P. xylostella, its primary natural enemies, and their susceptibilities to insecticides in order to develop an economically and environmentally sound integrated pest management program for collards in the state. Ecological life table studies of P. xylostella immature stages on collards located on the Eastern Shore and on Kentland Farm, near Blacksburg at the New River Valley, VA revealed that most (98 to 99%) of P. xylostella died from natural causes. Mortality factors varied between the two regions. Neonates, small larvae, and large larvae disappearing were major mortality factors. Rainfall, predation, and dispersal probably contributed the most to this mortality. Egg mortality played a bigger role at the New River Valley compared with the Eastern Shore. Three parasitoid species were found that contributed to the mortality of P. xylostella: Diadegma insulare (Cresson) (Hymenoptera: Ichneumonidae); Oomyzus sokolowskii (Kurdjumov) (Hymenoptera: Eulophidae); and Microplitis plutellae (Muesebeck) (Hymenoptera: Braconidae). Additional studies conducted in the laboratory using leaf-dip bioassays revealed that P. xylostella collected from the Eastern Shore of Virginia, showed significant tolerance levels to esfenvalerate, acetamiprid, methomyl, methoxyfenozide, indoxacarb, and acephate compared with a susceptible strain of P. xylostella. The highest tolerance ratio (1,876 fold) was to esfenvalerate, a commonly-used pyrethroid. All of the insecticides tested in this study were quite toxic to the adult stage of the parasitoids, D. insulare and O. sokolowskii. The insect growth regulator, methoxyfenozide was considerably less toxic than other insecticides such as esfenvalerate, methomyl, acephate, spinosad, indoxacarb, and emamectin benzoate at field-rate and 1% of field-rate concentrations. The aforementioned insecticides as well as some other insecticides were evaluated several times in the field for efficacy against P. xylostella as well as other pests of collards. The most efficacious insecticides over five field experiments included acephate, emamectin benzoate, esfenvalerate, methomyl, methoxyfenozide, novaluron, indoxacarb, and spinosad. These insecticides were followed in relative efficacy by Bt kurstaki, acetamiprid, and azadirachtin, which provided relatively inconsistent control of lepidopteran larvae over the experiments. Effective insecticide options in collards that are less toxic to natural enemies and that can fit well into integrated pest management programs include indoxacarb, spinosad, novaluron, emamectin benzoate, methoxyfenozide, and Bacillus thuringiensis subsp. kurstaki. / Ph. D.

The susceptibility of a population of diamondback moth, Plutella xvlostella L (Lepidoptera: Plutellidae), collected from Montgomery County, Virginia, and its ability to develop resistance to Bacillus thuringiensis was evaluated. The field population of diamondback moths was found to be susceptible to B. thuringiensis. Selection pressure at 153 I.U. of B. thuringiensis endotoxin per ml for nine generations did not cause any significant difference in mean mortality of third instar diamondback moths although there was a trend towards lower mortality, there was significant negative linear correlation between generation and mean mortality of diamondback moth larvae (P = 0.003, r²= 0.73). LC₅₀ increased from 264 I.U. of B. thuringiensis endotoxin per ml in generation I to 514 LU/ml in generation IX. The interrelationship of B. thuringiensis to diamondback moth and its primary parasitoid, Diadegma insulare Cress (Hymenoptera. Ichneumonidae), was studied by determining: the differential response of third instar diamondback moth, parasitized and unparasitized, to B. thuringiensis, and the ability of D. insulare to discriminate between B. thuringiensis-treated and untreated hosts. There was no significant difference (P > 0.05) between mean mortality of parasitized and unparasitized larvae at each of the three concentrations consisting of 154, 334, and 2237 I.U. of B. thuringiensis endotoxin per ml. The regressions of the response of parasitized and unparasitized larvae, however, were highly significant (P = 0.0001). The LC₅₀s of parasitized versus unparasitized larvae were 373 and 176 I.U./ml B. thuringiensis endotoxin, respectively. Female D. insulare did not discriminate between B. thuringiensis-treated and untreated hosts. The percentage of D. insulare females emerging from B. thuringiensis-treated larvae (41.4%) was not significantly different from that of untreated larvae (32.0 %). Mean mortality of third instar diamondback moth subjected to B. thuringiensis endotoxin at 153, 334, and 2237 I.U./ml were not significantly different at temperatures of 15 and 20 °C, but were significantly lower than that at 30 °C. The effects of B. thuringiensis endotoxin residues on leaves under room conditions [27 ± 1 °C, RH 27 ± 72%, and 8:16 (L:D)] were not significantly different at 2 and 192 hours after treatment. / Master of Science