They found that the higher linoleic-acid-concentration edible plant oils were more lethal. They also tested whether oils with a higher concentration of a polyunsaturated fatty acid called linoleic acid were more lethal than oils with lower linoleic acid concentrations. They hypothesize that the larger instars might be more vulnerable because they had higher respiratory demands and thus were more vulnerable to respiratory disruption by the oils. They found that mortality from the oils was higher for the third and fourth instars than for the first and second instars. Next, they exposed individuals from all four larval stages to these three most lethal edible plant oils. Njoroge and Berenbaum found that hempseed oil showed the highest lethality, followed by sesame and pumpkin seed oils. They recorded the number of larvae surviving at 24 hours and 48 hours. The oils they tested were canola, cashew nut, corn, cottonseed, grapeseed, hempseed, olive, peanut, pumpkinseed, sesame, soybean, sunflower, and walnut. Control groups were placed in cups with deionized water and no oil. In their first experiment, Njoroge and Berenbaum tested the lethality of 13 widely available edible plant oils on third-instar larvae of Aedes aegypti by placing larvae in plastic cups containing water and a plant oil. (Photo credit: Elijah Juma)Īedes aegypti has four life stages- egg, larva, pupa, and adult-and the larval stage has a progression of four instars. Teresia Njoroge is a Ph.D., candidate in the School of Integrative Biology at the University of Illinois at Urbana-Champaign. The goal of the study, Noroge says, was to “test the concept that edible oils can be an effective, non-toxic tool for the control of container-dwelling Aedes aegypti in the drinking water storage containers of people in settings that lack piped water systems.” The results of their research were published in March in the Journal of Medical Entomology. To explore plant oils as safe and environmentally friendly alternatives to chemical pesticides, Teresia Njoroge and May Berenbaum, Ph.D., at the University of Illinois at Urbana-Champaign tested the lethal effects of several edible plant oils on Aedes aegypti. And, because they act through multiple mechanisms-as repellents, larvicides, and oviposition inhibitors-it is harder for mosquitoes to evolve resistance to them. An alternative type of control mechanism, edible plant oils are inexpensive, easily available, non-toxic to mammals, and readily biodegradable. Chemical pesticides are a leading method of control, but pesticides pose economic costs, contribute to the evolution of insecticidal resistance, pose risks to the environment, and present safety concerns to humans and non-target animal species. Therefore, control of yellowfever mosquitoes is a critical public health priority. The yellowfever mosquito ( Aedes aegypti) spreads dangerous human arboviruses that include dengue, Zika, and chikungunya. (Photo credit: Flickr/ ukagriculture, CC BY-NC-ND 2.0) In a test of edible plant oils’ effects on larvae of the Aedes aegypti mosquito, researchers at the University of Illinois at Urbana-Champaign found that hempseed oil showed the highest level of lethality, followed by sesame and pumpkin seed oils.
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