Agriculture

Natural habitats

Crops

Green revolution

Machine Crops

Crops_genetically uniform

Miracle rice

Chief beneficiaries

Inorganic fertilizer

Irrigation

Pesticides

Dust bowl

Land clearing for farming

Soil erosion

Soil erosion

Salinization

Aquifer depletion

Waterlogging

Overgrazing

Ecological disruption

Weeds and pests

Weeds

Factors contributing to pest problem

Pest and Pest control

Insect pests

Some insect pests

Chemical control

Domestic crops were selected for maximum productivity and had little natural pest resistance Main Idea(s) of This Slide – Because farmers selected the varieties of their crops based upon productivity alone, they inadvertently eliminated the genetic variation that protected crops from natural pests. Without variation, whole crops are vulnerable to single pests species. Because of this, agriculture today relies upon pesticides. 28

Potato famine of Ireland was caused by genetically uniform crops and lack of pesticides to protect them Blight hits potatoes, 1845 Main Idea(s) of This Slide – Agricultural pests are any organism (insect, bacteria, fungi) that feeds upon crops. Historically, as well as today, pests have posed serious problems to agriculture. In 1845, a pest fungus attacked the potato crop in Ireland. Since Ireland was highly dependant on this one crop, the attack had devastating consequences; widespread famine resulted. This graph shows the effect of the potato blight on the population of Ireland. Based on: Population Reports, May 1992 29

Today’s Pests Pests attack and eat our food crops This problem is due, in part, to not selecting for pest resistance during domestication Main Idea(s) of This Slide – Attacks on agricultural crops occur today as pests feed upon all different parts of agricultural plants. Many agricultural crops are especially vulnerable due to the way they were domesticated. When early agriculturalists were domesticating the “staple” food crops, they selected for the types that had the highest yield of food instead of those types that were most resistant to pests. Because only those high-yielding strains were selected for, the crops now lack genetic diversity. Without diversity in the genetics of the crop plants, if a pest comes along that the crop is vulnerable to, then all of the crop will suffer. To combat this problem agriculturalists have had to employ widespread pesticide use. Based on: National Geographic, February 1980 30

DDT was invented in the 1940’s and viewed as: - miracle for farmers - and safe Main Idea(s) of This Slide – DDT (dichloro-diphenyl-trichloroethane) was developed in the 1940’s and was widely used on crops across the United States. It was highly effective in killing agriculture pests and was thought to be safe. 31

Arial crop sprayers were used to spray tons of DDT on crops across the U.S. Main Idea(s) of This Slide – DDT use was widespread across the country, with tons of it used agriculturally as seen in this slide. Photo courtesy of Texas Parks and Wildlife Department 32

Pests became resistant to DDT Main Idea(s) of This Slide – This image shows a caterpillar that is covered in pesticide crystals, but still alive. Over the years that DDT was used, pest populations began to respond to it by becoming resistant. Due to genetic diversity within the populations of pest species, some individuals were more tolerant of DDT than others. Those “more tolerant” individuals were the only ones who could successfully survive and reproduce. After many generations of this occurring, the population becomes dominated by resistant forms and DDT was no longer as effective as it once was. Farmers responded by using higher concentrations of DDT to combat these resistant forms. Based on: National Geographic 33

Pesticide Resistance In the beginning, most pests were sensitive to DDT but a few were resistant The resistant forms survived and reproduced In the end, most pests were resistant to DDT Main Idea(s) of This Slide – This illustration shows how pesticide resistance occurs. Looking at the top leaf we see diversity in the population. Most of the flies (colored white) are genetically predisposed to be susceptible to DDT and after exposure they die. Other flies in the population (colored orange) are genetically more tolerant of DDT and some of them survive the exposure and reproduce. The next generation has a higher number of genetically tolerant forms. After the next exposure to DDT, many of the flies are not killed. Based on: National Geographic, February 1980 34

Bio-magnification The concentration of pesticides in higher levels of food chains Main Idea(s) of This Slide – Biomagnification occurs when toxins begin to accumulate in body tissues of members of a food chain. In the case of DDT, insects consumed the DDT and built up a level of DDT in their body tissues. Later, when predators ate many insects, they ended up with an even higher concentration of DDT than the insects had. When a top predator consumes the lower predators, the DDT levels become even higher. 35

Trophic Levels Most food chains consist of four trophic levels Main Idea(s) of This Slide – This chart displays a typical food chain containing 4 trophic levels. In biomagnification, with each step up the food chain, the concentrations of toxins will become higher. Based on: Mader, S., Inquiry Into Life, McGraw-Hill Most food chains consist of four trophic levels 36

Energy Available to Consumers at Next Trophic Level Energy Lost by Death and Decay Energy Lost by Respiration Energy Lost by Excretion Energy Lost by Egestion of Feces Main Idea(s) of This Slide – This illustration shows how energy is lost as it is transferred from one organism to another. Energy is released through respiration, excretion of waste, and repair of damage. While energy is lost from the consumer, the toxins which they have consumed are not metabolized and released. So each time the consumer eats a prey item, the concentration of toxins increases. Energy Ingested 37

DDT in Food Chain DDT is concentrated as it moved up food chain This is because energy is lost (from respiration) as go up food chain but DDT is not Main Idea(s) of This Slide – This illustration shows how DDT would become more and more concentrated as it moves from producers to the top carnivores. Based on: Campbell et al, Biology: Concepts and Connections, Benjamin Cummings 38

Overview of Lesson Pests, DDT and biomagnification DDT, eagles and falcons Species endangered Organic foods Advance Organizer This portion of the lesson will describe the effects that DDT biomagnification have had on the American bald eagle and peregrine falcon populations in the U.S. 39

Bald Eagle Once was widely distributed over U.S. As a top carnivore it feeds on fish Swoops down and captures fish off the surface of the water Main Idea(s) of This Slide – The American bald eagle is a top carnivore that once was widely distributed across the U.S. Fish are one of its primary prey items. Photo courtesy of Texas Parks and Wildlife Department 40

Scientists discovered that DDT was concentrated in the bald eagle DDT affected the eagle’s ability to reproduce Main Idea(s) of This Slide – Because the eagles were the top carnivore in the food chain, DDT became concentrated in their body tissues. The DDT was originally absorbed by the plants on which it was sprayed. It then passed into the body tissues of the insects who consumed the plants. Insectivores (fish) then absorbed the DDT when they ate insects who had DDT in them and had a much higher concentration in their body tissues. Finally, when eagles consumed the fish, they ended up with toxic levels of DDT in their body tissues. The DDT impaired the eagles ability to reproduce. Photos courtesy of Texas Parks and Wildlife Department 41

Nests contained broken, rotten eggs Scientists found that the eagle eggs had thin egg shells and broke easily Nests contained broken, rotten eggs The number of young produced per breeding pair was reduced Main Idea(s) of This Slide – Scientists discovered that eagles who had built up levels of DDT in their body tissues laid eggs that had very thin shells. The thin-shelled eggs broke easily, causing a much higher mortality of young than was natural. 42

Population of adult eagles declined to 4,000 and the eagle was listed as “Endangered” Main Idea(s) of This Slide – Over the years of DDT use, the eagle population dropped to approximately 4,000 and the eagle was listed as an “Endangered Species.” Photo courtesy of Texas Parks and Wildlife Department 43

The Environmental Protection Agency (EPA) banned DDT in 1972 (USA) Main Idea(s) of This Slide – In 1972, the EPA banned the use of DDT in the United States. Photo courtesy of Texas Parks and Wildlife Department 44

Eagle reproduction before and after DDT ban Main Idea(s) of This Slide – This graph shows that the number of young per breeding pair fell dramatically during the years when DDT was widely used, and that it increased again after DDT was banned. The concentration of DDE, the breakdown product of DDT, was lower in eggs after the ban. Based on: Grier, J., Science, 1982 45

Eagle populations increased rapidly and the eagle is now listed as “Threatened” Main Idea(s) of This Slide – Once DDT was no longer used, the eagle population recovered quickly and was soon listed as “threatened” instead of “endangered.” From: Time, July 11, 1994 46

Peregrine Falcon Occurred naturally over most of continental U.S. Nests on cliffs Keen eyesight (if human, could read newspaper print at 110 yards) Feeds on other birds, knocking them out of the sky at 200 m.p.h. Main Idea(s) of This Slide – The peregrine falcon is another top carnivore who was also impacted by the use of DDT. These falcons are known to nest on cliffs where they can scan the sky for prey items (smaller birds, small mammals). These birds have extremely keen eyesight and can fly at speeds over 200 miles per hour. Photo courtesy of Texas Parks and Wildlife Department 47

DDT & Peregrine After DDT was introduced in 1940s, DDT weakened the birds’ egg shells, devastating the population By early 1970s, the entire U.S. population was down to 12 breeding pairs Peregrines were declared federally endangered and DDT banned Peregrines were bred in captivity and reintroduced successfully in cities Photos courtesy of Texas Parks and Wildlife Department Main Idea(s) of This Slide – Peregrine falcons responded to DDT the same way eagles did; their eggs became extremely thin and fragile. By the early 1970’s the population of peregrine falcons in the United States had declined to only 12 breeding pairs (24 individuals). Captive breeding has helped to replenish the peregrine population. Populations have now been established in cities throughout the U.S. Cities offer favorable habitat as the falcons build nests on the tops of buildings which mimic their natural cliff habitats. 48

poisoning

Good insects

Red Fire ant

Red fire ant

Prickly pear Prickly pears were imported into Australia in the 19th century for use as a natural agricultural fence, but quickly became a widespread weed, rendering 40,000 km² of farming land unproductive. The Cactoblastis moth, a South American moth whose larvae eat prickly pear, was introduced in 1925 and almost wiped out the infestation. This case is often cited as a "textbook" example of successful biological pest control. The same moth, introduced accidentally further north of its native range into southern North America, is causing serious damage to some native species in that area.