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Horizontal distribution of Diabrotica longicornis (Say) eggs around plants was random in three Quebec cornfields. Vertically, 72% and 24% eggs occurred in the surface 10 cm soil before and after fall plowing, respectively. A 5 x 10 cm x 15 cm (deep) sampling unit was appropriate for estimating egg populations before plowing. Thereafter, 20 cm depth was needed. Larvae and pupae were concentrated around the root system and a soil quadrat 20 x 20 cm x 10 cm (deep) was an easily reproducible sampling unit. Direct counting on corn plants in early morning was the most efficient method for adult sampling. Sample sizes for all stages were calculated for different precision levels. Spatial distribution of eggs and larval field populations were contagious, and a stratified random sampling is appropriate for density estimation. Spatial distribution of adults changed with corn phenology. Average mortality of overwintering eggs was 66% and of spring larvae 89%. The field population density of beetles did not change significantly during 1979-82.

Thesis (Ph.D.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on May 1, 2009) Vita. Includes bibliographical references.

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The southern corn rootworm (Diabrotica undecimpunctata howardi Barber) is the primary soil insect pest to peanuts (A rachis hypogaea L.) in Virginia and North Carolina. The newer cultivars, which are planted on the majority of the acreage, have not been extensively screened for rootworm resistance. The objective of this study was to evaluate 5 new Virginia-type cultivars (NC-V 11, VA-C 92R, VA 93B, NC 10C, and AgraTech VC1) and 18 breeding lines (N90013E, VA 861101, VA 9211920, VA 9211289, VA 891438, VA 901072, VA 9010343, VA 8911115, VA 9109213, VA 9109235, VA 9109237, VA 9111309, N93007L, N92066L, N92074L, PI 121067, GP-NC 343, N92064L and N93003L) for resistance to southern corn rootworm in the laboratory and in the field. NC 7 and NC 9 were used as susceptible checks. NC 6 was used as a known resistant check. Rootworm mortality and feeding were measured from bioassays in the lab. Pod damage data were obtained from field plots. NC 6 caused some significant differences with more rootworm mortality at both the pupal and adult stages than NC 7, NC 9, NC 10C, NC-V11, N90013E, PI 121067, AgraTech VC-1, VA 93B, VA 861101, and VA 9211290 when feeding on peanut seedlings. In addition, NC 6 also caused significantly higher mortality at pupa and adult stages than NC 7, AgraTech VC-1, VA 861101, and VA 93B when larvae fed on the peg and immature pod tissue from field plantings. NC 6 also had less total pod damage than NC 7 in natural infestations of southern corn rootworm. Results from this study indicate that NC 61s are still the only cultivar that demonstrates resistance to rootworm. / Master of Science

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The thesis aims to optimize the methods of laboratory culture and to fill in the gaps in knowledge of D. virgifera virgifera ecophysiology. The experiments on embryology and development proved that the diapause of D. virgifera virgifera is of obligatory type and can be terminated by exposure to long-day conditions (20:4; photo : scotophase) and constant temperature of 25 °C. Approximately 10% of eggs completed the development to adults within 4 months. Besides numerous other environmental conditions that are discussed, temperature seems to be a key factor influencing longevity in this pest. Higher temperature of 25 °C prolonged survival by more than 20 days in 2015, compared to 22 °C in 2014.

<p>The western corn rootworm (WCR) <i>Diabrotica virgifera virgifera</i> Leconte is a major pest of maize in the United States. Currently, it is principally managed using Bt maize hybrids and neonicotinoid seed treatments (NSTs), which were concurrently introduced in the early 2000s. This simultaneous release, and subsequent rapid adoption, created a situation in which Bt maize hybrids were never assessed in the absence of NSTs, and vice versa. Consequently, neonicotinoids’ influence on refuge function, primarily whether these insecticides aid or hinder the production of a sufficient population of susceptible beetles to delay resistance, has not been assessed. Moreover, a mounting suite of detrimental environmental effects of NSTs have been documented, lending some urgency to questions about their necessity.</p><p>To determine the influence of NSTs on refuge function, untreated and treated Bt maize fields were planted with 5% untreated refuge marked with ¹⁵N. Throughout the field seasons of 2019 and 2020, adults were collected from these fields and analyzed to determine their natal host plant. Results documented that the numbers of refuge beetles produced by the 5% seed blend are likely insufficient to result in rates of mating to delay resistance development.</p><p>To determine if the effect of using NSTs in combination with Bt maize hybrids is additive, synergistic, or neutral at managing secondary soil pests in the Midwest, four 16 block fields were planted in 2018, 2019 and 2020 comparing four treatments (1. Untreated, Bt seed; 2. NST, Bt seed; 3. Untreated, non-Bt seed; 4. NST, non-Bt seed). Compact method sampling, root rating, and yield were used to document the presence of secondary soil pests. All three sampling years documented low abundance of white grubs and wireworms. There was minimal influence of NSTs on maize yield (2018: p = 0.07; 2019: p = 0.62; 2020: p = 0.056) and root damage (0-3 scale) (2018: M = 0.0092; 2019: M = 0.0091; 2020: M = 0.0361). These same fields were used to document the presence of NSTs in soil, as well as residues in nearby waterways. Results documented greatest soil and water clothianidin levels earlier in the season and declined as the season progressed.</p><p><br></p>