A study was undertaken to obtain information on farmers' knowledge, attitudes and practices regarding pesticide usage and to determine the amount of pesticide in soil and water samples collected at four cotton producing areas of Mali. The results from a survey of 24 farmers identified various concerns regarding personal and environmental safety. Despite their training, sometimes growers did not use pesticides in an appropriate manner. Highly toxic pesticides are used by farmers with insufficient personal protective equipment. Sixty soil samples and eight water samples from four cotton growing areas in Mali were scanned for detectable levels of fifty pesticides in total. Pesticides were detected in 77% of the soil samples and the main pesticides were p,p-DDT and its breakdown products, endosulfan I endosulfan II, endosulfan sulfate and profenofos. Among the pesticides detected, p,p-DDT use in the study area had not been reported during the past ten years. The most common pesticide detected in the soil samples from cotton growing areas studied was endosulfan II constituting 65% of the detections with a maximum amount of 37 ng/g. Residues detected in soil samples were below the quantification limit for the newer cotton production region of Kita and for the intermediate region of San. Eight pesticides were detected in water samples: γ-BHC (lindane), endosulfan I, endosulfan II, endosulfan sulfate, dieldrin, p,p-DDD, p,p-DDE and atrazine. All detected pesticides in water had concentrations below the quantification limit except for atrazine. Even though pesticides were found at low concentrations in ground water samples, the fact that water from these wells is used for human and animal consumption is of concern. Also, soil pesticides may be taken up by plants and passed on to other organisms feeding on those plants. Further residues studies in the cotton growing areas of Mali are in order to monitor pesticides residues in Malian soils, water and living organisms. / Master of Science

<p dir="ltr">Specialty crop growers in the Great Lakes region of the United States and Canada have been struggling for decades to manage the carrot weevil (<i>Listronotus oregonensis</i>). In carrot, parsley, and celery production, growers may experience 40-100% yield loss, despite the intensive use of insecticides (Boivin, 1999; Jasinski, 2008; Telfer et al., 2019). To improve sustainable management of this native pest in commercial vegetable production, we must address existing knowledge gaps in carrot weevil mate-finding behavior, population genetic diversity and gene flow, and grower adoption and efficacy of integrated pest management (IPM) strategies, like cultivar selection, to combat this pest. To date, these factors have not been evaluated in the carrot weevil system, yet together they have significant implications for developing novel monitoring tools, grower decision making, and the potential evolution of insecticide resistance in this damaging pest.</p><p dir="ltr">To address knowledge gaps in grower adoption and the efficacy of IPM strategies, such as cultivar selection, I investigated the influence of carrot cultivar on the oviposition preference of carrot weevil in the laboratory and quantified the diversity of insect assemblages on carrots in Ohio and Indiana. In tandem, I delivered an online survey to specialty crop growers in Indiana and Ohio to measure their knowledge and use of insect-resistant cultivars as a part of an IPM strategy. I found that carrot cultivar did not impact carrot weevil oviposition preference, but rather the number of petiole trichomes was positively correlated with the cumulative number of egg scars found on a given carrot cultivar. Similarly, cultivar did not influence the diversity of insect assemblages associated with carrot foliage, but hemipterans were the dominant group found across cultivars. Moreover, insect diversity across all carrot cultivars was high, with Shannon-Weiner diversity indices ranging from 2.14 to 2.45.</p><p dir="ltr">I analyzed survey responses from vegetable growers regarding their knowledge, current use, and future use of insect-resistant cultivars and found no significant differences between conventional or organic growers, in either Indiana or Ohio, or across experience levels regarding their knowledge and current or future use of insect-resistant cultivars. Although a greater number of organic growers were aware of insect-resistant cultivars, they were not incorporated into their IPM plans. In contrast, half of responding conventional growers indicated implementing insect-resistant cultivars in current IPM plans. Growers indicated that more information about the efficacy, costs, and benefits of insect-resistant vegetable cultivars would be most helpful in informing their decision to incorporate this IPM tactic on their farms.</p><p dir="ltr">To address knowledge gaps regarding carrot weevil mate-finding behavior, I investigated behavioral response to conspecific frass using Y-tube bioassays and the volatiles of frass samples were analyzed using gas-chromatography mass-spectrometry (GC-MS) as starting points to assess the presence of volatile chemical cues that might function as sex or aggregation pheromones. I found that male and female weevils oriented strongly towards volatiles from male frass. However, conspecifics were not attracted to mixed or female frass, suggesting male frass contains behaviorally relevant chemical cues that are unique or present in greater abundance than in female frass. When I analyzed the chemical abundance and composition of the male frass volatiles, I found 16 common compounds across all samples and no compounds were unique to the male volatile blend. Specifically, (1S)-6,6-dimethyl-2-methylene-Bicyclo[3.1.1]heptane and (1R)-2,6,6-Trimethylbicyclo[3.1.1]hept-2-ene were present in significantly higher abundance in extracts of males frass compared to those of female frass.</p><p dir="ltr">Finally, to address knowledge gaps in the genetic diversity and gene flow of carrot weevil populations in the Great Lakes Region of the U. S., I used single nucleotide polymorphisms (SNPs) to compare genetic diversity and structure of agricultural populations of carrot weevil in Michigan and Ohio. I found limited genetic differentiation between three carrot weevil populations collected from celery and parsley fields located in Michigan and Ohio. I also found high inbreeding coefficients and heterozygote deficiency in all populations, suggesting that all carrot weevil populations are locally confined. These results suggest significant gene flow between populations, which has implications for management, specifically the mitigation and management of insecticide resistance.</p><p dir="ltr">Together, the results from my dissertation can be applied to the improvement of carrot weevil IPM across the Great Lakes region of the United States and Canada. Further investigations into the impact of physical characteristics, specifically petiole trichomes, on carrot weevil oviposition behavior can inform the breeding and development of resistant carrot cultivars. Results from my behavioral bioassay studies represent a critical first step towards the identification of an aggregation or sex pheromone, which would greatly improve detection of resident carrot weevil populations when used in conjunction with current monitoring traps. My results also suggest that monitoring and mitigation of insecticide resistance in carrot weevil populations should be considered at the regional scale, at minimum, with significant gene flow between carrot weevil populations within the Great Lakes Region.</p>