Pesticides

What is a pest? An organism that interferes with human welfare and activities Insects Weeds

Why do we need pesticides? Insects eat and destroy crops Weeds compete with crops Insects carry disease

Benefits of pesticides Allows more food production Farmers can save $3-$5 in crops for every $1 invested in pesticides Protects people from disease

DDT used to fight Malaria Sri Lanka in the early 1950’s, more than 2 million cases of Malaria Began spraying DDT to kill the mosquitos carrying the disease Cases dropped to 0 Discontinued spraying and malaria cases jumped up to 1 million per year Began spraying again and still do in over 20 tropical countries

Disadvantages Often kill non-target species Pesticide residue on crops Persistent in environment- affects animals up the food chain People working closely with pesticide at risk of health problems

Types of Pesticides Chemical pesticides Not naturally occurring Toxic Persistent in the environment Affect non-target species Examples- Crabamate Pesticides, Organochlorine pesticides (DDT), Organophosphate pesticides

Chemical Pesticides Crabamate Pesticides Organophosphate Pesticides Affects non-target species Affect the nervous system Effects are usually reversible Organophosphate Pesticides Highly toxic Not as persistent in the environment

Chemical Pesticides Organocholorine Insecticide Very persistent in the environment Affects non-target species Effects nervous system Removed from the market due to health effects Examples include DDT

Organic pesticides Naturally occurring in the environment Plants have developed natural resistance to pest Can be used naturally or made synthetically Easily degradable in environment Not persistent Can be toxic to aquatic organisms and pollinators

Biopesticides Microbial pesticides Made from microorganisms - fungi and bacteria Plant-incorporated protectants Genetically alter plant to produce its own pesticide Biochemical Naturally occurring substances that control pests

Major problems with Pesticides Pest species (plant and animal) develop resistance to pesticides Pesticides that don’t degrade easily can cause problems for humans and other organisms Bioaccumulation - build up of pesticides in body Biomagnification - organisms higher up in the food web have higher concentrations of pesticides in their body

Alternative Integrated Pest management

Integrated Pest Management (IPM) A general philosophy of safe & effective pest control that uses several different methods of control to reduce the population of a particular pest Involves identifying & understanding each pest, its life cycle, breeding sites, and density threshold (# of pests per area that can be tolerated without overall crop damage) & selecting remedies that address the specific pest problem

Steps of Integrated Pest Management Six Steps of IPM Implement preventive strategies. 2. Scout plants for symptoms or presence of pests. 3. Identify pests and scope of damage. 4. Determine when action must be taken. 5. Implement management strategies. 6. Evaluate results.

Integrated Pest Management (IPM) Strategies Development of resistant varieties: some plants are naturally resistant to insects, some produce their own pesticides, some produce odors that discourage pests, some produce chemicals that interfere with an insect’s nervous system and some contain chemicals that make an insect unable to digest food Resistant varieties reduce the need for spraying synthetic pesticides Developing resistant varieties in time consuming & expensive

Integrated Pest Management (IPM) Strategies Use of Beneficial Insects: beneficial wasp species are the most useful insects for controlling the populations of important insect pests such as gypsy moth larvae, cutworms boll weevils, hornworms, and mealy bugs Introduction of the Paraguayan wasp, a parasite of the mealy bug, helped to protect Cassava (an important food crop in Africa) Not all insects are good biological controls – praying mantises are not selective & will eat all insects, not just the pests

Integrated Pest Management (IPM) Strategies Microbial pesticides: viruses, protozoa, bacteria & fungi can be used to control certain insect pests Bacillus popillae is a bacterium that causes milky spore disease in Japanese beetles; it is sprayed on the soil where the beetle larvae live & when the larvae die, the bacterial spores are released into the soil & continue to control the beetle larvae It is expensive to establish the spores that cause milky spore disease and it is only effective if the entire neighborhood uses it

Integrated Pest Management (IPM) Strategies Biochemical pesticides: use naturally occurring substances that control pests by nontoxic methods, such as pheromones Pheromones are sex attractants that can be used to bait traps; synthetic sex attractants have been produced and used to control fruit flies in Florida & California Cannot be used on all species – there is no practical or economical way to hang dispensers containing female pheromones high in forest trees, where they are needed to control gypsy moths The correct distribution of pheromone is necessary to disrupt the mating process

Integrated Pest Management (IPM) Strategies Cultivation Practices: timing the planting and harvest to avoid pests can reduce damage to some crops Mixing crops - reduce monocultures Delaying the planting of wheat prevents Hessian flies from laying eggs on young wheat plants Plowing under the cover crop residue of cotton eliminates winter habitat for insect pests such as the boll weevil

Integrated Pest Management (IPM) Strategies Synthetic Pesticides: SLAM is a low-insecticide bait made from powdered wild buffalo gourd root and carbaryl insecticide (one ounce per acre); these chemicals are like candy to the rootworm beetle and they eat so much of it that it takes little insecticide to kill them – farmers only spray when needed Biological controls have significantly reduced the amount of synthetic pesticides used but they have not replaced the use of pesticides entirely

Integrated Pest Management (IPM) Strategies Computer Programs: help farmers reduce the amount of pesticides they use Spraying only when the number of insects will reach damaging levels (not when few insects present) Spraying only when the insect is in its larval stage (not after the cocoon is spun = too late)

Benefits of Biological Controls Usually cheaper to use than chemical controls Don’t pollute the environment Often kill only the pest, not beneficial insects

Disadvantages of Biological Controls Biological controls are often more expensive to develop (must travel to country of origin to find natural predators & diseases – bring back & study under quarantine) Less profit for companies – companies will not invest time & money on research without a financial incentive Effective biological controls for many insect pests are not yet available

Disadvantages of Biological Controls Some biological controls require cooperation of surrounding neighbors in order to be effective Some farmers are unwilling due to the ease of using chemical pesticides Biological controls are slow-acting whereas chemical pesticides are fast acting