D. Shell, SMHS 2014

Boll Weevil

Natural Pest Control

Pests = any species that compete with humans for food, invade lawns & gardens, destroys wood in houses, spreads disease, or is a nuisance. Weed = specific to plants that compete with crops.

There is a natural balance in undisturbed ecosystems which keeps pest populations in check: plants and other insects kill them off

When people disrupt natural ecosystems by planting monoculture crops, tree farms, & lawns, some of the natural predators of pests are killed off

Developed countries use ¾ of all pesticides, but use is growing fast in LDCs

Spiders are one of the best natural predators of insect pests

2 crops (cotton & corn) use 90% of insecticides & 80% of herbicides Pesticide Basics

Active ingredients (the chemical that kills the pest) vs inactive ingredients (additional chemicals that aren’t involved)

5 types: Insecticides (bugs); herbicides (plants); nematicides (roundworms); fungicides (fungi); rodenticide (rodents) The “perfect” pesticide

Narrow spectrum = kills only the bad bugs (not helpful bugs)

readily decomposes = breaks down so it doesn’t biomagnify

stay where it is placed = doesn’t move around in environment Insecticides

First Generation Insecticides (natural) (early civilization – 1920s) o toxic inorganic minerals: sulfur, arsenic, lead, & mercury o very persistent & harmful to people

Botanicals used: o Ex: nicotine sulfate (from tobacco leaves), pyrethrum (from mums), and rotenone (from roots of certain plants) o biodegrade quickly, but very toxic to bees & aquatic organisms

Second Generation Insecticides (synthetic & organic) (1920’s - today) o Chlorinated hydrocarbon pesticides (ex. DDT)

broad spectrum (kills many bugs including good guys) persistent (1963 Rachel Carson’s book Silent Spring make people aware of problems & it is later BANNED in

1972) o Organophosphate pesticides (ex. Malathion, diazinon)

persistence less than chlorinated hydrocarbons, but more toxic to humans, bees, birds, & aquatic organisms although good for animals that they are less persistent, dangerous for humans to spray w/o protective gear

o Pyrethroids (chemically altered botanicals, more effective) biodegrade quickly, but very toxic to bees & aquatic organisms

o Carbamates (ex. Sevin) Some pesticides, broad-spectrum agents = are toxic to many species. Herbicides

selective herbicides (kill only certain types of plants) Ex: Weed-B-Gone

broad-leaf herbicides – kill broad-leaf plants (dicots) o note: during Vietnam War, Agent White, Agent Blue, & Agent Orange were used to defoliate the jungle to expose

enemies. Cause a lot of environmental damage & valuable trees replaced by bamboo & grasses (soldiers got sick too)

grass herbicides – kill narrow leaf grasses (monocots)

nonselective herbicides (kill all plants) Ex: Round-Up Benefits of Pesticides

Save human lives: kill insects that carry disease (ex. Malaria-mosquitoes, bubonic plague-rat fleas, typhus-lice & fleas, & sleeping sickness-tsetse fly)

DDT very effective at killing mosquitoes (countries with malaria have lifted ban on DDT)

Increase food supplies & lower food costs (kill bugs, weeds, & plant disease) (estimated that 37% of crops are lost before and after harvest because of pests even with pesticides)

Increase profit for farmers

Work faster & better than alternatives: easily stored, used, and are safe when handled properly

getting more target specific pesticides (only kill bad guys)

genetic engineers developing pest-resistant crop strains Problems with Pesticides

Biggest concern: pests develop genetic resistance to pesticides. Insects breed rapidly& have short life spans = quick evolution. 520 insects, 273 weeds, 150 plant, & 10 rodent species are completely resistant to one or more pesticide

when pests develop resistances, farmers are told to use more pesticide, apply more frequently, or switch to different pesticides; result is farmers paying more for pest control that is less effective

o “Pesticide Treadmill” = pest develops resistance, stronger pesticide used, pest develops resistance, stronger pesticide used, pattern continues.

D. Shell, SMHS 2014

Broad-spectrum insecticides kill beneficial natural predators & parasites

wiping out major predators may result in a relatively harmless pest gaining strength & becoming a problem (takes over empty niche)

Although pesticide use has increased 33 fold since 1942, food supply lost has remained about the same

Persistence, Bioaccumulation, & Biomagnification (pesticides that don’t degrade work up food chain & get more concentrated) ex. DDT

persistent pesticides get into soil, groundwater, lakes & streams

Less than less than 2% of insecticides & 5% of herbicides applied aerially or ground spraying reach their target; end up in surface waters, groundwater, bottom sediments, foods, people, and wildlife

Harm Wildlife: fish-eating birds particularly hurt b/c of DDT (made the birds egg shells too fragile for the birds to reproduce – bald eagle’s problem), also hurts food chains (killing birds of prey increased small animal populations). DDT has been banned in US since 1972.

Threats to Human Health

acute exposure causes nausea, vomiting, organs damage, or death

many workers in developing countries are poisoned each year (applied by hand)

chronic exposure increases cancer risk or birth defects (ex. 2,4-D causes lymphoma)

even trace exposure may affect endocrine system

nine persistent pesticides suspected of interfering with hormones in animals & humans (small genitalia, decreased sperm counts, miscarriages, etc.)

children may be especially susceptible because 84% of US homes use pesticides & kids play on grass more than adults (flea collars, bug bombs, herbicides for dandelions, etc.)

Farm workers are most likely to be poisoned due to repeated exposure

DDT & other chlorinated hydrocarbon pesticides replaced by organophosphates which have less persistence, but are more toxic to us

Regulations

Federal Insecticide, Fungicide, & Rodenticide Act 1947, ‘72, ‘96 (FIFRA) o requires that all commercial pesticides be approved by the EPA for general or restricted use. o pesticide companies evaluate active ingredients, EPA approves, then sets tolerance levels o The EPA canceled or restricted the use of 55 active pesticides between 1972 & 1996 including banning many chlorinated

hydrocarbon insecticides, some carbamates & organophosphates, and herbicides 2,4,5-T & Silvex

Some studies say that he EPA, FDA, and USDA don’t do enough enforcement. Alternatives to Pesticides

Better cultivation practices (physical): o crop rotation (specific bugs can’t build up #’s) o plant rows of hedges around fields to provide natural habitats for predators o use polyculture methods of farming (NO MONOCULTURE – with one type of crop there is too much food for pest in one

area) o adjust planting times to times when the pest isn’t active

Use natural enemies (biological): (Biological Controls- bugs, viruses, bacteria) o pros: focuses on selected target species; is nontoxic, can be self-perpetuating once populations start o cons: years of research needed to pick right predator; predators can’t always be mass produced; slower results;

unpredictable results, may eat beneficial insects

Pheromones & Hormones (chemical) o Pheromones. = sex “scents” specific to species: put scent on trap to attract bugs to trap o Hormones = chemicals that aid development of bug, add chemicals that screw hormones up so bug can’t grow right

Genetically Engineered (GE) crops (biological) – pesticide Bt gene is added to corn, so plant makes its own pesticide

Botanicals (biological) = pyrethroids & similar compounds

Zap food with radiation (physical) = gives longer shelf life (kills mold, bacteria)

Vacuum pests from crops (physical)

Spray with hot water (physical) = scalds pests

Introduce sterile males (biological)

Noises that repel pests (physical)

Physical barriers (physical) - ex: use nets

Integrated Pest Management (most effective method) o mixture of biological, chemical & physical methods listed above o minimizes use of chemical pesticides by individually tailored plan or use

narrow-spectrum pesticides