Thesis (M.Sc.). / Written for the Dept. of Plant Science. Title from title page of PDF (viewed 2009/06/18). Includes bibliographical references.

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Regulation of nutritional intake by herbivorous insects often leads to optimal performance. When given choices, beet armyworm, Spodoptera exigua, caterpillars selected a diet with a protein to digestible carbohydrate ratio of 22p:20c. Restriction to carbohydrate-biased diets led to increased mortality and developmental time. On protein-biased diets, caterpillars possessed metabolic strategies to maintain optimal performance. / Caterpillar glucose oxidase (GOX), which catalyzes the oxidation of glucose, may be a pre-ingestive mechanism to cope with excess dietary carbohydrates. GOX activity was highest in the labial salivary glands of 4th instar caterpillars and was higher in caterpillars reared on a meridic artificial diet (AD) compared to those fed Medicago truncatula. Following transfer from plants, labial salivary GOX activity increased with time spent on AD suggesting that a dietary factor is involved in this enzyme's regulation. Dietary carbohydrate levels do not appear to regulate GOX activity; however nutritional content may play a role its regulation.

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Insecticides in the diamide class have a novel mode of action and have become a key component for management of agriculturally important lepidopteran pests since their introduction in 2008. Corn earworm, Helicoverpa zea (Boddie); and the armyworm complex including fall armyworm, Spodoptera frugiperda (J.E. Smith); and Spodoptera exigua (Hübner); are significant pests of agroecosystems in the Mid-southern and Southeastern regions of the United States. They have developed resistance to, and/or inconsistent control has occurred with most chemical classes. The objectives of this study were to establish susceptibility levels of field populations of H. zea, S. frugiperda, and S. exigua collected in the Mid-southern and Southeastern regions of the United States to flubendiamide and chlorantraniliprole. To achieve equivalent levels of mortality for each species, a higher concentration of flubendiamide was required compared to chlorantraniliprole. Furthermore, two experiments were conducted to determine the systemic and residual efficacy of chlorantraniliprole and flubendiamide against H. zea on vegetative and reproductive structures of soybean. Chlorantraniliprole moved systemically and had significantly greater control than flubendiamide in the systemic and residual study out to 31 DAT. Flubendiamide did not move systemically but provided significant residual control out to 31 DAT compared with the untreated control. Neither insecticide was detected in reproductive structures. Finally, to determine the risk of resistance development, a S. exigua colony, originating from a field collection in 2013, was separated into three cohorts that were independently selected with three concentrations (0.016, 0.020, and 0.025 ppm) of flubendiamide incorporated into a meridic diet. These concentrations were chosen from the LC30, LC60 and LC90 of the original colony. Resistance ratios never increased past 2.11old. The highest resistance ratios occurred after 18 generations for the LC30 colony, 19 generations for the LC60 colony, and 13 and 15 generations for the LC90 colony. After reaching their highest point of resistance, the colonies began to decline in egg production and larval survivability and did not recover. After 22 generations the selected colonies were terminated. The results from this portion of the study suggest that the potential for resistance development of beet armyworm to flubendiamide is unclear.

The tethered-flight technique used previously for studies of the factors regulating the flight performance of Spodoptera exem_p ýto moths was improved and developed to increase reliability and incorporate computerised datalogging permitting faster and more extensive analysis. Larvae of S. exempta show a density-dependent phase polyphenism and tee ect of larval phase on adult flight was examined. A consistently greater flight performance was observed in female moths reared as re aria larvae compared with those reared as solitaria, but no significant effect was found in males. The distribution of flight durations was examined and found to be log-normal. Using normalised data the heritability of flight duration was estimated in a number of strains. Significant heritabilities were obtained for flights beginning before, but generally not after, midnight when radar observations in the field have shown flights achieving substantial displacements to occur. It is suggested that prolonged flights in the laboratory which start before midnight and whose durations are under genetic regulation represent migratory flights in the field. Shorter flights, particularly those starting after midnight, achieve local redistribution of moths, some of them possibly representing the "pluming" behaviour observed using radar. Flight duration was shown to respond to selection for both short and long flight. The Fl generations of the lines of four strains selected for increased flight capacity revealed a bimodal distribution of flight durations indicating two types of moth. It is suggested that a major gene could account for this effect and that-the longer fliers represent potential migrants while the shorter fliers are capable only of flights achieving local dispersal. The effect of flight on the fecundity of females was examined. It was found that in moths subsequently fed water (necessary for oocyte development), a decrease in fecundity resulted which was related to the duration of flight. In moths fed sucrose fecundity was maintained at the level of unflown moths. These results are discussed in relation to the behaviour and ecology of S. exempta in East Africa and the prospects for the success of a regional approach to its control.

The introduction of pyramided Bacillus thuringinesiss (Bt) in field corn, Zea mays L. has helped reduce kernel and foliar damage from caterpillar pests including fall armyworm, Spodoptera frugiperda (J.E. Smith) and corn earworm, Helicoverpa zea (Boddie). These pests can also be controlled with diamide insecticides. No compensation for manual kernel damage occurred at any section of the ear for Bt or Non-Bt corn. No consistent impacts on corn growth or yield were observed following foliar applications of diamide insecticides at various growth stages. The diamides exhibit longer residual efficacy than other insecticides available for fall armyworm management in field corn. Based on the level of mortality observed on young tissue developed after treatment with chlorantraniliprole, chlorantraniliprole translocated in corn and could therefore be more beneficial than other insecticides when applied during vegetative growth stages.

During 2016 and 2017, studies were conducted to determine the effects of Spodoptera frugiperda (J.E. Smith) on both damage and yield of Sorghum bicolor (L.) Moench and Zea mays (L.) when infested during the whorl stage. Results from damage ratings suggest that as the amount of overall plants infested increased, overall damage rating increased. However, yield results suggested that there was no yield loss as percent infested plants increased. Other studies were conducted to determine the most sensitive vegetative growth stages of grain sorghum and field corn. Manual damage studies suggests that extensive damage to field corn during growth stages V9 to V15 will cause significant yield loss. Also, damage to grain sorghum after growth stage V8 and prior to boot stage can cause significant yield loss.

Laboratory and field studies of the fall armyworm, <i>Spodoptera frugiperda</i>, were undertaken to determine if a high larval rearing density produces premigrant traits, and if these traits can be used as criteria for separating nonpremigrant from premigrant groups. An increase in larval rearing density significantly decreased pupal weight and forewing width in the laboratory but not in the field. The greatest differences in developmental time among laboratory density treatments were 0.6 d and 1.07 d for females and males, respectively, but differences were not considered biologically significant. Rearing density did not affect duration of pupal stage in the field-reared fall armyworms. An actograph was used to measure adult flight activity and was validated with videotape recordings of moths in actograph cages. Behaviors other than flying occurred; hence, computer-recorded counts were termed activity counts (one activity count was recorded each time a moth broke an infrared beam directed through a window in an actograph cage). Male moths showed a greater proportion of long-duration activity bouts (spells of activity), a significantly greater activity bout duration, and a generally greater magnitude of activity during peak periods than female moths. Generally, actograph activity was not significantly affected by rearing density. Both mated and unmated females exposed to males showed very little actograph activity, and most of the females mated when exposed to males, regardless of rearing density. An increase in rearing density in the laboratory significantly increased adult lipid reserves, but higher lipid reserves were not related to a higher activity potential. Although larval rearing density did not affect wing-loading values, the fall armyworm as a migrant species showed lower than theoretically expected wing-loading values. Because some premigrant traits were produced by increasing the rearing density and other premigrant traits and behaviors were not produced, it is inconclusive that premigrants were produced by these rearing methods. Based on these results and data taken from the literature, there is reason to believe that the fall armyworm does not have a separable premigrant phase, and that components of weather are more influential than larval density in initiating its migratory behavior. / Ph. D.

The Fall Armyworm is a serious pest of many crops throughout most of the Western Hemisphere particularly those belonging to the family Gramineae. This pest is usually controlled by insecticides which, however, cause many health and environmental problems. Although a rich bank of sorgum germplasm occurs in Yemen, no effort has been made to identify the Yemeni cultivars which might express resistance to armyworm attack. There is very little information to show at what time of the growing season and at what planting stage the sorghum cultivars are most susceptible to armyworms. Therefore, eight Yemeni and two American sorghum cultivars were planted in Tucson, Arizona, during 1983 and 1984. The experimental design was a randomized complete block arranged in split-split plots with four replications. The main plots were the varieties, and subplots were two planting dates and two infestation times. The plants were artificially infested with laboratory reared, first instar larvae. Infestation consisted of five larvae per plant in 1983 and ten in 1984. Results demonstrate the 'IBB' and 'TURBA' received the least leaf damage and 'SGIRL-MR1' and 'ALBAIDA' received the most in 1983. However, during 1984, 'TURBA' and 'HAIDRAN' showed the greatest degree of resistance and 'SGIRL-MR1', 'AMRAN', 'ALMAHWIT', and 'ALBAIDA' the least.