Rainfastness of insecticides is an understudied aspect of agricultural research. Little is known about the residual of commonly used products for key pests of cotton, as well as their residual after a rainfall event. This project was designed to evaluate the impact of rainfall on the performance of commonly used insecticides for tobacco thrips, Frankliniella fusca (Hinds); tarnished plant bug, Lygus lineolaris (Palisot de Beauvois); and bollworm, Helicoverpa zea (Boddie), management in cotton. Laboratory and field experiments suggest that rainfall occurring within 16 hours after application had a negative impact on the performance of most insecticides. Chemical analyses of leaf tissue using a mass spectrometer confirmed what was observed with field and laboratory experiments. Although direct comparisons between insecticides cannot be made, results from this study suggest that spinosyns and insect growth regulators appeared to have the longest residual after a rainfall event.

The bollworm, Helicoverpa zea (Boddie), is an economically important pest of cotton and is becoming more difficult to control in the United States. This project was designed to develop a better understanding of the effects of resistance development and plant structures on the efficacy of Bt cotton and foliar insecticides. Experiments examined larval behavior and damage in current cotton varieties expressing proteins from Bacillus thuringiensis. Other experiments examined the effects of floral structures on the control of bollworm using foliar insecticides. Results suggest that larval feeding and avoidance behavior is dependent on point of eclosion. Fruiting form damage increased in two-gene cotton compared to earlier research but was low in cotton expressing the Vip3A protein. Increases in damage can lead to more frequent applications of foliar insecticides. Floral structures can hinder insecticide efficacy by reducing exposure. Results from these experiments will be important for refining management recommendations for bollworm in Bt cotton.

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This report includes the determination of activity and possible mode of action for a group of potential new insecticides. The biological screening procedure was developed using Drosophila melanogaster as the test organism while Musca domestica was used for mode of action assays. The percent kill for each compound is based on the number of eggs placed on media containing the insecticide minus the number of adults enclosed as compared to the control media reared flies. Observations were made on all stages from eggs through adults to determine time of death and if any malformations were present. These observations aided in the mode of action studies as did preciously published work on diflurbenzuron. The mode of action studies encompassed chitin synthesis, chitin breakdown and DNA synthesis. Cuticle deposition was determined gravimetrically on pupal instar reared on media with and without DOWCO 416. Chitin synthesis and DNA synthesis were followed by measuring the incorporation of radiolabeled precursors by pupal instars reared on media with and without DOWCO 416. Chitin breakdown was followed through the measurement of chitinase activity spectrophotometrically on all stages of larvae which were reared on media with and without DOWCO 416. Direct inhibition of chitinase was investigated by incubation of the purified chitinase from Staphlycoccus griseus with varying concentrations of the test compound.

Chlorpyrifos is a widely used organophosphate insecticide, functioning through the inhibition of acetylcholinesterase. Recent studies report negative long-lasting biochemical and behavioral effects at levels without acetylcholinesterase inhibition. Our lab studies have identified the endocannabinoid system as a target for OP low-dose neurotoxicity. This thesis identifies the proteins and their associated neurotransmitter systems in the hippocampus that have been affected by low dose developmental exposure to the OP insecticide CPF. Male rat pups were treated from postnatal day 10 (PND) - PND16 with either corn oil (vehicle), 0.75 mg/kg of CPF, or 0.02 mg/kg of PF-04457845, a specific fatty acid amide hydrolase (FAAH) inhibitor. On PND38, rats were sacrificed for hippocampal extraction, and shotgun proteomics was used for protein expression. DAVID and Ingenuity Pathway Analysis software detected differentially expressed proteins such as Neuroligin-2 and Synaptotagmin 2, and disrupted signaling pathways such as ephrin B signaling, synaptogenesis signaling, and glutamate receptor signaling. Taken together, our data suggests that CPF reduces glutaminergic signaling pathways, greatly reducing long-term potentiation, prohibiting proper synapse formation, and therefore disrupting the proper functioning of the hippocampus.

The inheritance of resistance to chlordane in the German cockroach, Blattell germanica. (L.), was studied by determining the toxicity of chlordane to the following strains of roaches: a) chlordane-resistant and non-resistant strains, b)F₁ and F₂ progeny of reciprocal crosses between two parental strains, c) progeny of pair matings within resistant and non-resistant strains, and from a cross between resistant females and non-resistant males. / Ph. D.

Malaria is vectored by the mosquito Anopheles gambiae (Ag) in Sub-Saharan Africa and infects approximately 500 million people annually. The increasing prevalence of pyrethroid-resistant mosquitoes has amplified the need for development of new, selective mosquitocides for use on insecticide-treated nets. We have developed several phenyl-substituted N-methylcarbamates producing a high degree of selectivity for Anopheles gambiae acetylcholinesterase (AgAChE) over human AChE. Molecular models suggest alternate conformations (flexibility) of W84 and W431 (Ag numbering) at the hydrophobic subpocket of the AgAChE active site and poor flexibility within human AChE, allowing for the high selectivity of our novel carbamates. Initial selectivity data was obtained through screening of these insecticides while using ethanol as a solvent. Re-screening of these carbamates in the presence of 0.1% DMSO (v/v) resulted in antagonism of inhibition for AgAChE, thus reducing the AgAChE-selectivity by at least 10-fold. However, the presence of 0.1% DMSO did not antagonize the inhibition of human, Drosophila melanogaster, or Musca domestica AChE. Non-selective carbamates also displayed no solvent-dependent antagonism of inhibition in any species studied, including AgAChE. Molecular models provide an explanation for antagonism of inhibition when DMSO is present. I, and collaborators, propose that W84 and W431 in AgAChE comprise an allosteric pocket that is stabilized by DMSO and is responsible for the solvent-dependent antagonism of inhibition observed with AgAChE. / Master of Science in Life Sciences

Two age factors were studied: the age of the roach at the time of testing, and the age of the female parent at the time reproduction occurred. Age groups from 1-3 days to 25-28 days were used to test the first factor and the first three egg eases were used to test the latter. Age was found to be a statistically significant factor when malathion, aldrin, and DDT were tested on both sexes of the normal strain. However, because of inconsistencies and a lack of differences of any great magnitude, it is believed that the differences in all but the aldrin tests were of no biological significance. In the aldrin tests it appeared that as the age of the roach increased, susceptibIlity gradually increased. The tests using aldrin on the Aldrin-resistant strain were significant for the females. Resistance in this strain appeared to increase from the 1-3 day age group until it reached a peak in the 10-12 day age group, then decreased to a level equal to or lower than that of the younger age groups. Statistical significance was found for the parental age factor in about one-half of the tests. However, it was of little biological significance because the variations were of a small magnitude and inconsistencies between the males and females occurred of ten. / Master of Science

Preliminary experiments in Virginia by Wallace and Turner (1961) on face fly control indicated that there was some promise using low-level feeding of a chemical such as ronnel in a mineral salt mixture as a larvicide. In cooperation with the Moorman Manufacturing Company and Mr. H. C. Stuart of Elk Garden, Virginia, a large scale experiment was initiated in the spring of 1962 . Approximately 1600 head of cattle in 23 pastures were utilized in this experiment. All of the pastures received a mineral salt mixture containing 5.5 percent ronnel with the exception of two pastures on the perimeter of the treated area that received no ronnel and were used as checks. Adult and larval counts were made on 7 of the 23 treated pastures and both of the untreated pastures. Results indicated that: (1) In spite of good larval control adult fly counts remained high, especially in treated pastures near untreated areas. Apparently the face fly has a natural tendency for dispersion, and, therefore, area control by low-level feeding of salt containing a larvicide is difficult. (2) When the consumption of ronnel remained above 5.5 mg per kg of animal body weight per day, larval control was above 95 percent. (3) During hot, dry periods animals reduced their salt consumption and this resulted in decreased larval control. (4) When salt boxes were placed in areas where cattle were seldom seen to frequent, salt consumption was lowered, as was larval control. / Master of Science

Malaria continues to cause significant mortality in sub-Saharan Africa and elsewhere, and existing vector control measures are being threatened by growing resistance to pyrethroid insecticides.  With the goal of developing new human-safe, resistance-breaking insecticides we have explored several classes of acetylcholinesterase inhibitors.  In vitro assay studies have shown that trifluoromethyl ketones (TFK's) are potent inhibitors of An. gambiae AChE (AgAChE), that inhibit the enzyme by making a covalent adduct with the catalytic serine of the enzyme.  However research in the Carlier group has shown that trifluoromethyl ketones bearing benzene and pyrazole cores have shown very little toxicity to An. gambiae, perhaps due to hydration and rapid clearance. Focus was directed towards synthesis of oximes, oxime ethers, and hydrazones as potential prodrugs to prevent immediate hydration and reach the central nervous system.  The synthesis of various oximes, oxime ethers, and hydrazones has been shown to give cimpounds toxic to Anopheles gambiae within 3- to 4-fold of the toxicity of propoxur. However, thus far we have not been able to link the toxicity of these compounds to a cholinergic mechanism.  Pre-incubation studies suggest that significant hydrolysis of these compounds to TFKs does not occur or 22 h at pH 7.7 or 5.5.   Future work will be directed towards TFKs that have better pharmacokinetic properties.  Work will also be directed at synthesis of oxime and hydrazone TFK isosteres to determine the mechanism of action of these compounds. / Master of Science