Entomology Publications Entomology 1-9-1991 Toxicity and Neurotoxic Effects of Monoterpenoids: In Insects and Earthworms Joel R. Coats Iowa State University, [email protected] Laura L. Karr Iowa State University Charles D. Drewes Iowa State University Follow this and additional works at: http://lib.dr.iastate.edu/ent_pubs Part of the Entomology Commons, Environmental Health Commons, Other Animal Sciences Commons, and the Plant Biology Commons The ompc lete bibliographic information for this item can be found at http://lib.dr.iastate.edu/ ent_pubs/377. For information on how to cite this item, please visit http://lib.dr.iastate.edu/ howtocite.html. This Book Chapter is brought to you for free and open access by the Entomology at Iowa State University Digital Repository. It has been accepted for inclusion in Entomology Publications by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Toxicity and Neurotoxic Effects of Monoterpenoids: In Insects and Earthworms Abstract The insecticidal activity of several monoterpenoids from essential oils was evaluated against insect pests. Toxicity tests illustrated the bioactivity of d-limonene, α-terpineol, β-myrcene, linalool, and pulegone against insects, including the house fly, the German cockroach, the rice weevil, and the western corn rootworm. Bioassays were conducted to assess their toxicity via topical application, fumigation, ingestion, and ovicidal exposures. Growth, reproduction and repellency were also evaluated in the German cockroach. Non-invasive electrophysiological recordings were used with an earthworm to investigate neurotoxic effects of the monoterpenoids. Relevant monoterpenoid bioassay results in the literature are also discussed. Disciplines Entomology | Environmental Health | Other Animal Sciences | Plant Biology | Plant Sciences Comments Reprinted (adapted) with permission from Naturally Occurring Pest Bioregulators, 449(20); 305-316. Doi: 10.1021/bk-1991-0449.ch020. 1991 American Chemical Society. This book chapter is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/ent_pubs/377 Chapter 20 Toxicity and Neurotoxic Effects of Monoterpenoids In Insects and Earthworms Joel R. Coats, Laura L. Karr1, and Charles D. Drewes Department of Entomology and Department of Zoology, Iowa State University, Ames, IA 50011 The insecticidal activity of several monoterpenoids from essential oils was evaluated against insect pests. Toxicity tests illustrated the bioactivity of d-limonene, α-terpineol, ß-myrcene, linalool, and pulegone against insects, including the house fly, the German cockroach, the rice weevil, and the western corn rootworm. Bioassays were conducted to assess their toxicity via topical application, fumigation, ingestion, and ovicidal exposures. Growth, reproduction and repellency were also evaluated in the German cockroach. Non-invasive electrophysiological recordings were used with an earthworm to investigate neurotoxic effects of the monoterpenoids. Relevant monoterpenoid bioassay results in the literature are also discussed. Many essential oils from plants possess biological activity against pests that could be harmful to the plant. Some exhibit acute toxicity, while others demonstrate repellent, antifeedant, or antioviposition effects or inhibition of growth, development or reproduction (1). Many of the fragrant volatile oils contain ten- carbon hydrocarbons, or their related alcohols, ketones, aldehydes, carboxylic acids, and oxides, and are termed monoterpenoids. Most Publication Date: January 9, 1991 | doi: 10.1021/bk-1991-0449.ch020 are considered secondary plant chemicals, with little direct metabolic importance, but with considerable coevolutionary Downloaded by IOWA STATE UNIV on March 18, 2016 | http://pubs.acs.org significance (2). Plant-insect interactions have been studied for many years, but a better understanding of these complex coadaptive relationships could provide a basis for using plant-derived chemicals in biorational approaches for better management of pest organisms (3). Botanical insecticides such as pyrethrins and rotenone have proven to be both safe and effective in controlling insect pests. An improved knowledge of the monoterpenoids (as well as sesquiterpenes, diterpenes, triterpenes, tetraterpenes) and their effects on insects contributes to unraveling the intricate interactions that have shaped the coevolution of insects and plants. It also provides leads for possible utility of these safe, degradable compounds in modern pest control, and, as more advanced genetic engineering capabilities develop, the potential for Current address: DowElanco, Walnut Creek, CA 94598 O097-6156/91A)449-O305$06.00/0 © 1991 American Chemical Society Hedin; Naturally Occurring Pest Bioregulators ACS Symposium Series; American Chemical Society: Washington, DC, 1991. 306 NATURALLY OCCURRING PEST BIOREGULATORS exploiting their efficacy by transferring genes to different crops or by selecting for the protective chemicals in breeding programs. Figure 1 shows the structures of 2 cyclic and 2 acyclic monoterpenoids. Knowledge of the spectrum of insecticidal activity is limited for most of the terpenoids. The results of d-limonene trials against a wide range of insect groups indicate that this important constituent of citrus oil is toxic to some life stages of some species via some routes of exposure (4,5,6,7). Its utility as a broad-spectrum insecticide, however, does not seem feasible. Spectrum of repellent activity has been evaluated for several types of terpenes, and reproductive effects have been described for some chemicals (1,8). Mechanisms of acute toxicity have not been elucidated for the monoterpenoids, but the onset of symptoms is usually rapid, manifested as agitation, hyperactivity, and quick knockdown (4,5.) • Our investigations have also included electrophysiological studies of the toxic effects of monoterpenoids on nerves. Methods Topical applications to house flies (Musca domeatica) and German cockroaches (Blattella germanica), fumigation of German cockroaches and rice weevils {Sitophilus oryzae) and repellency to German cockroaches were conducted by methods described previously (4). The toxicity by ingestion and effects on growth and reproduction were evaluated by incorporation of the chemicals into the ground cat chow diet of the German cockroaches (9). Lavicidal and ovicidal activity against the western corn rootworm (Diabrotica vergifera vergifera) were tested in petri dishes of soil and on moist blotter paper, respectively (4). Repellency of terpenoids was evaluated with German cockroaches in choice tests, using pairs of plastic boxes (9 X 8.5 X 2cm) connected by plastic tubing. Treated filter paper was placed in one box, and a control (acetone treated) filter paper was put in the other box (4). Hedgeapple, bay leaves, and spearmint chewing gum were tested using the weight of products (in ug) per unit of volume of the box (in cnr) for determination of exposure concentrations (1 /jg/cnr = 1 ppm). Neurotoxicity was assessed in the earthworm Eisenia fetida using non-invasive electrophysiological techniques described previously (10). The earthworms were exposed in a vapor/contact method in which a small volume of terpenoid was delivered onto a moist filter paper in a vial which was then closed tightly (11). Periodically, worms were placed on an etched circuitboard recording grid for electrophysiological testing, and giant fiber activity Publication Date: January 9, 1991 | doi: 10.1021/bk-1991-0449.ch020 associated with the escape response was monitored (12.). The method Downloaded by IOWA STATE UNIV on March 18, 2016 | http://pubs.acs.org has been used previously to examine sublethal effects of pesticides on earthworm neural activity (13). Bioassay responses were calculated as LD50's, ED50's or ET50's using the trimmed Spearman-Karber method (14). Duncan's multiple range test and analysis of variance were used for the repellency trials, and the paired comparison t-test was used to analyze the food preference experiments. Results and Discussion I. Acute Toxicity. The utility of an insecticide has often been judged by its immediate and acute actions on pest species of insects. Terpenoids can effect toxicity symptoms very rapidly via contact or vapor exposures, including hyperactivity and tremors. Their degree of potency is significantly less than conventional synthetic organic insecticides, often by orders of magnitude. However, their actions can be very effective under circumstances that allow brief high-concentration uses of generally safe Hedin; Naturally Occurring Pest Bioregulators ACS Symposium Series; American Chemical Society: Washington, DC, 1991. 20. COATS ETAL. Toxicity and Neurotoxic Effects of Monoterpenoids 307 pulegone Fig. 1 - Structures of 4 monoterpenoids Publication Date: January 9, 1991 | doi: 10.1021/bk-1991-0449.ch020 Downloaded by IOWA STATE UNIV on March 18, 2016 | http://pubs.acs.org Hedin; Naturally Occurring Pest Bioregulators ACS Symposium Series; American Chemical Society: Washington, DC, 1991. 308 NATURALLY OCCURRING PEST BIOREGULATORS chemicals (e.g., greenhouses, animal shampoos and dips, fumigations). Research has been limited to a few insect species and a few terpenoids, but the results of the topical treatments, fumigations, and repellency studies indicate that the monoterpenoids can exert substantial toxicity alone, or with a synergist, and demonstrate considerable repellent activity as well. Very