PESTICIDES, USES AND EFFECTS OF Paul C. Jepson Oregon State University I. Classification and Uses cides. Benefits that include improved yield, crop quality, II. Efficiency and food safety and reductions in vector-borne disease III. Ecotoxicology and Management incidence have driven, and will continue to drive, their use. The earlier synthetic organic compounds were, however, flawed in their environmental behavior. They were persistent, they had a very broad spectrum of GLOSSARY toxicological activity, and they displayed a tendency to be magnified in concentration through food chains, pesticide A chemical substance used for controlling, such that damage was inflicted to animal populations preventing, destroying, or mitigating a pest or- that lived beyond the treated area in habitats that were ganism. not intentionally contaminated. The discovery of some of these limiting impacts was only made possible through technical advances in, for example, analytical PESTICIDES HAVE BEEN IN RECORDED USE since chemistry and conceptual advances where, for example, 1000 B.C. Arsenic was in regular use as a garden insecti- the ability to predict environmental behavior from cide in China by A.D. 900 and chemicals of one form chemical properties only developed after pesticides had or another have protected humans and their crops and been in use for decades. New pesticide discoveries are livestock throughout the development of modern civili- no longer accompanied by the marvel and optimism zation. In comparison with this long time scale, we are that characterized the first synthetic insecticides. Our still in the earliest phases of the use of synthetic organic ability to exploit these materials has, however, advanced pesticides, which were first used over large areas in the considerably in recent years, and the chemicals them- 1940s. There has, nonetheless, been sufficient time for selves are increasingly specific in their impacts and several generations of pesticide chemistry to evolve, appear to pose reduced risks. Scientists still question and pesticides have influenced all habitats and have the value of reliance upon chemical pesticides, however, affected the lives of all their inhabitants over this period. and modern pest control is characterized in general by a cautious approach to their management and use. Set in a volume that will be consulted largely by I. CLASSIFICATION AND USES biologists and ecologists with an interest in biodiversity, this article summarizes the chemicals that are in most Nowhere have the costs and benefits of modern technol- widespread use and outlines the processes that contrib- ogy been more difficult to reconcile than with pesti- ute most to efficient delivery to the biological target. The Encyclopedia of Biodiversity, Volume 4 Copyright 2001 by Academic Press. All rights of reproduction in any form reserved. 509 510 PESTICIDES, USES AND EFFECTS OF TABLE I dients in a pesticide formulation include the AI, sol- Classification of Pesticides by the Type of Pest Controlled vents, carriers, surface-active agents, and specialized additives. Solvent choice is determined by the solubility Acaricide Mites, ticks, and spiders of the AI, potential toxicity to target plants (phytotoxic- Adulticide Adult insects ity), toxicology, flammability, volatility, and cost. Some Algicide Algae solvents are not miscible in water and cause emulsions Arboricide Trees, brush, and scrub to be formed (e.g., xylene), whereas others are selected Avicide Birds because of their ability to dissolve the AI and their Bactericide Bacteria ability to dissolve in water (e.g., isopropyl alcohol). Fungicide Fungi Carriers can include inert clays that disperse the active Herbicide Plants ingredient through a powder or granular formulation. Insecticide Insect and sometimes related arthropod pests, Surface-active ingredients are used to assist in the pro- including mites cess of emulsion formation (the dispersion of the pesti- Ixodicide Ticks cide liquid within the liquid diluent), but they also Larvicide Insect larvae include wetting agents (materials that reduce surface Miticide Mites, ticks, and spiders tension and enhance wetting and coverage of surfaces), Molluscicide Mollusks, such as slugs and snails dispersing agents (materials that maintain the emulsion Nematicide Nematodes as microscopic droplets within the diluted formula- Ovicide Invertebrate eggs tion), and spreading agents (materials that enhance cov- Piscicide Fish erage of waxy plant foliage and insect cuticles). Predacide Vertebrate Predators The pesticide formulation may be in solid (i.e., Rodenticide Rodents, including rats and mice powder or granule) form, or it may be a liquid or gas Silvicide Trees, brush, and scrub concentrate. Modern pesticides may achieve their Termiticide Ants and termites intended effects at rates of less than 10 g per hectare (10,000 m2 ϭ 1 ha), and the formulation blend enables these tiny quantities to be distributed evenly over the intended target surface. nature and importance of toxicological and ecological A two-letter code denotes the formulation type on all effects are then reviewed, followed by a summary of pesticide labels, and this is a fundamentally important procedures through which pesticides are regulated and aspect of the selection of a pesticide for a particular managed. This article does not provide detailed reviews use. There are four groups of formulation types: of biochemical mode of action, application, formula- tion, or environmental fate and behavior in any detail, • Group 1: Concentrates for dilution in water, includ- and readers are recommended to pursue some of the ing DC (dispersable concentrate), EC (emulsifiable literature in the bibliography to gain insight into these concentrate), SC (suspension concentrate), and WP important areas of pesticide science. (wettable powder) • Group 2: Concentrates for dilution with organic sol- A. Uses of Pesticides vents, including OL (oil-miscible liquid) and OP (oil-dispersable powder) Pesticides may be classified by the types of pest they • Group 3: Formulations to be applied undiluted, in- control (terms often bearing the suffix-cide; Table I) or cluding GR (granules) and UL (ultra-low-volume by the effects that they have upon the pest organism (ULV) liquids) (terms that do not bear the suffix-cide; Table II). • Group 4: Miscellaneous formulations, including RB (bait) and AE (aerosol dispenser) B. Classification of Pesticides 1. Formulations Pesticides are marketed in complex mixtures, or formu- 2. Pesticide Types lations, containing the pesticide chemical itself, the ac- Pesticides are characterized by their chemical diversity tive ingredient (AI), and additives that enhance mixing also. The summary below includes many of the most and dilution in water or oil and release or deliver the important groups of chemicals used in crop protection, toxic material once it has been applied. Common ingre- but it is not exhaustive. Some pesticide properties are PESTICIDES, USES AND EFFECTS OF 511 TABLE II Classification of Pesticides by Effects on Pests Antifeedant Inhibits feeding while insects remain on the treated plant Antitranspirant Reduces transpiration Attractant Lures pest to a specific location Chemosterilant Prevents reproduction Defoliant Removes foliage without immediately killing plant Desiccant Causes plant parts to dry Disinfectant Destroys or inactivates harmful organisms Feeding stimulant Causes vigorous feeding Growth regulator Stops, speeds up, or retards growth in insects or plants Repellent Drives away pests without killing them Semiochemical Pheromones and other substances emitted by plants or animals that alter animal behavior Synergist Substance that enhances the effects of a pesticide sufficiently uniform within the major classes of chemi- toxicity. Some have adverse effects on wildlife, includ- cals for this broad classification to be used in selection ing toxicity to fish. Examples include neem tree (Azadi- of chemicals for a particular use. Biochemical mode of racta indica) oil, which is used to protect stored prod- action, for example, tends to be similar within major ucts from insects; pyrethrum, from Chrysanthemum classes, and many crop protection programs use materi- cinerariaefolium, a powerful but rapidly degraded insec- als from several classes to avoid excessive selection ticide that affects the peripheral nervous system, caus- pressure for resistance to pesticides. Other properties, ing paralysis, known as ‘‘knockdown’’; nicotine (from are, however highly variable within pesticide classes as Nocotiana tabacum), an alkaloid insecticide that is also well as between them. These include vapor pressure a neuromuscular poison in vertebrates; and rotenone, (volatility) and the various partitioning coefficients that from the roots of Derris and Lonchocarpus spp., also determine the distribution and fate of the active ingredi- used as a piscicide. Some of these materials are widely ent in the environment. These properties determine the used in locally made or commercial formulations, and effectiveness of the pesticide against a specific target although they may be highly toxic, many are not persis- or in a specific climate type or habitat, and detailed tent in the environment and degrade rapidly in sunlight knowledge of these properties is required for pesticide or when exposed to microbial activity in soil or water. selection to be effective. Some aspects of properties will Each material has unique properties, and it is not possi- be dealt with in Section II. ble to make generalizations about toxicology