Environmental factors exert a great effect on the occurrence of aphids and thrips, their abundance and damage done in cereal crops, as well as the time of appearance of these pests in the crops, timing of their control and means used. Species diversity of aphids and thrips in winter rye, triticale, wheat, and spring barley was identified. Variation of the abundance of the main species of aphids and thrips in the mentioned crops was determined in relation to crop growth stages and environmental factors. For the first time in Lithuania we estimated migration activity of R. padi and S. avenae using a suction trap and compared with the abundance of these aphid species in cereal crops. The experimental data obtained in this study enables assessment of damage done by aphids and thrips in winter rye, triticale and wheat crops and estimation of expedience of the application of aphids and thrips control measures. Thrips threshold of harmfulness at which it is expedient to apply control measures was identified in winter rye.

Cruciferous crops comprise one of the major crop divisions and contribute significantly to global crop production. Insect pests associated with cruciferous crops have the potential to destroy harvests. The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae) and cabbage aphids, Brevicoryne brassicae (L.) and Lipaphis erysimi (Kaltenbach) (Homoptera: Aphididae) are considered the most important cabbage pests in South Africa. Pest control in cabbage is still heavily reliant on use of insecticides even though insecticide application usually result in increased pest status of P. xylostella. Use of integrated pest management (IPM) strategies may yet prove invaluable as a means of suppressing the more serious cabbage pests. Global interest in cultural control strategies, that includes intercropping of unrelated crop plants, has been rekindled because of problems experienced with pesticide use. A study that involved the planting of two field trials with cabbage and carrot plants in different ratios, as a substitutive intercropping system, was undertaken during the 2002/03 and 2003/04 planting seasons. Field trials had five treatments viz. control (cabbage monoculture sprayed with mercaptothion), cabbage monoculture (without chemical application), 1:1 intercropping (cabbage:carrots), 1:3 intercropping and 1:5 intercropping, replicated six times in a randomized block design. Insects were sampled weekly by removing the third-youngest open leaf, from one plant per plot (six plants per treatment). Feeding damage to cabbage leaves was assessed visually by rating 14 plants per plot according to a numeric scale based on damage severity. P. xylostella and aphid parasitism levels were determined. Prominence values were calculated for P. xylostella larvae and aphids for each treatment per sampling date. P. xylostella infestations and parasitism levels were significantly (P ≤ 0.05) lower in control treatments. Intercropping ratio did not have a significant impact on pest infestations. P. xylostella infestations and parasitism on intercropping treatments did not differ significantly (P > 0.05) from that on monoculture plots (except for 1:5 intercropping during the 2003/04 season). Cotesia plutellae (Hymenoptera: Braconidae) was the dominant parasitoid and parasitism levels were significantly correlated with P. xylostella infestation levels. Prominence values showed a decline in P. xylostella infestations on intercropping treatments towards the last sampling date during both seasons. Feeding damage severity was lowest on the control treatment but similar for other treatments for both seasons. Aphid infestations were significantly (P ≤ 0.05) lower on the control treatment, but did not differ significantly between intercropping treatments. Aphid prominence values indicated possible suppression of infestations at low population levels during the early part of the season. Aphid parasitism was low during both seasons. It seems more likely that the reduction in insect infestation levels reported from the literature are related more to spatial arrangement of plants than cropping ratios. The observed suppression of aphid infestation levels on intercropped plots early in the season may be valuable in reducing the need for early chemical applications. The limiting of early insecticide application against aphids may result in a reduced pest status of P. xylostella, due to the conservation of C. plutellae populations. / Thesis (M. Environmental Science))--North-West University, Potchefstroom Campus, 2007.

Cruciferous crops comprise one of the major crop divisions and contribute significantly to global crop production. Insect pests associated with cruciferous crops have the potential to destroy harvests. The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae) and cabbage aphids, Brevicoryne brassicae (L.) and Lipaphis erysimi (Kaltenbach) (Homoptera: Aphididae) are considered the most important cabbage pests in South Africa. Pest control in cabbage is still heavily reliant on use of insecticides even though insecticide application usually result in increased pest status of P. xylostella. Use of integrated pest management (IPM) strategies may yet prove invaluable as a means of suppressing the more serious cabbage pests. Global interest in cultural control strategies, that includes intercropping of unrelated crop plants, has been rekindled because of problems experienced with pesticide use. A study that involved the planting of two field trials with cabbage and carrot plants in different ratios, as a substitutive intercropping system, was undertaken during the 2002/03 and 2003/04 planting seasons. Field trials had five treatments viz. control (cabbage monoculture sprayed with mercaptothion), cabbage monoculture (without chemical application), 1:1 intercropping (cabbage:carrots), 1:3 intercropping and 1:5 intercropping, replicated six times in a randomized block design. Insects were sampled weekly by removing the third-youngest open leaf, from one plant per plot (six plants per treatment). Feeding damage to cabbage leaves was assessed visually by rating 14 plants per plot according to a numeric scale based on damage severity. P. xylostella and aphid parasitism levels were determined. Prominence values were calculated for P. xylostella larvae and aphids for each treatment per sampling date. P. xylostella infestations and parasitism levels were significantly (P ≤ 0.05) lower in control treatments. Intercropping ratio did not have a significant impact on pest infestations. P. xylostella infestations and parasitism on intercropping treatments did not differ significantly (P > 0.05) from that on monoculture plots (except for 1:5 intercropping during the 2003/04 season). Cotesia plutellae (Hymenoptera: Braconidae) was the dominant parasitoid and parasitism levels were significantly correlated with P. xylostella infestation levels. Prominence values showed a decline in P. xylostella infestations on intercropping treatments towards the last sampling date during both seasons. Feeding damage severity was lowest on the control treatment but similar for other treatments for both seasons. Aphid infestations were significantly (P ≤ 0.05) lower on the control treatment, but did not differ significantly between intercropping treatments. Aphid prominence values indicated possible suppression of infestations at low population levels during the early part of the season. Aphid parasitism was low during both seasons. It seems more likely that the reduction in insect infestation levels reported from the literature are related more to spatial arrangement of plants than cropping ratios. The observed suppression of aphid infestation levels on intercropped plots early in the season may be valuable in reducing the need for early chemical applications. The limiting of early insecticide application against aphids may result in a reduced pest status of P. xylostella, due to the conservation of C. plutellae populations. / Thesis (M. Environmental Science))--North-West University, Potchefstroom Campus, 2007.

No description available.

Thesis (M.S.)--Georgia Southern University, 2007. / "A thesis submitted to the Graduate Faculty of Georgia Southern University in partial fulfillment of the requirements for the degree Master of Science." In Biology, under the direction of Alan Harvey. ETD. Electronic version approved: July 2007. Includes bibliographical references (p. 59-64) and appendices.

Thesis (M.S.)--Oregon State College, 1960. / Typescript. Includes bibliographical references (leaves 67-69). Also available on the World Wide Web.

Thesis (Ph.D. (Botany)) - Rhodes University, 2008.

Thesis--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references (p.57-63).

Thesis (Ph. D.) -- Lincoln University, 2009. / Also available via the World Wide Web.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1959. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 172-187).