Factors contributing to Factors contributing to pest problempest problem
Domestic crops were Domestic crops were selected for maximum selected for maximum
productivity and had productivity and had little little natural pest resistancenatural pest resistance
Blight hits potatoes, 1845
Based on: Population Reports, May 1992
Potato famine of Ireland was caused by genetically uniform crops and lack of
pesticides to protect them
Pests attack and Pests attack and eat our food cropseat our food crops
This problem is This problem is due, in part, to not due, in part, to not selecting for pest selecting for pest resistance during resistance during domesticationdomestication
Today’s PestsToday’s Pests
Based on: National Geographic, February 1980
DDT was invented in the DDT was invented in the 1940’s and viewed as:1940’s and viewed as:- miracle for farmers- miracle for farmers- and safe- and safe
Arial crop sprayers Arial crop sprayers were used to spray were used to spray tons of DDT on tons of DDT on crops across the crops across the U.S.U.S.
Photo courtesy of Texas Parks and Wildlife DepartmentPhoto courtesy of Texas Parks and Wildlife Department
Pesticide ResistancePesticide Resistance
In the beginning, most In the beginning, most pests were sensitive to pests were sensitive to DDT but a few were DDT but a few were resistantresistant
The resistant forms The resistant forms survived and reproducedsurvived and reproduced
In the end, most pests In the end, most pests were resistant to DDTwere resistant to DDT
Based on: National Geographic, February 1980
Bio-magnificationBio-magnification
The concentration of The concentration of pesticides in higher levels of pesticides in higher levels of
food chainsfood chains
Most food chains consist of four trophic levels
Based on: Mader, S., Inquiry Into Life, McGraw-Hill
Trophic Levels
Energy Available to Consumers at Ne
xt Trophic Level
Energy Lost by Respiration
Energy Lost by Death and Decay
Energy Lost by Excretion
Energy Lost by Egestion of Feces
Energy Ingested
DDT is concentrated as DDT is concentrated as it moved up food chainit moved up food chain
This is because energy This is because energy is lost (from respiration) is lost (from respiration) as go up food chain but as go up food chain but DDT is notDDT is not
DDT in Food Chain
•Pests, DDT and biomagnification•DDT, eagles and falcons•Species endangered•Organic foods
Overview of Lesson
Bald EagleBald Eagle
•Once was widelyOnce was widely distributed over U.S.distributed over U.S.
•As a top carnivore it As a top carnivore it feeds on fishfeeds on fish
•Swoops down and Swoops down and captures fish off the captures fish off the surface of the watersurface of the water
Photo courtesy of Texas Parks and Wildlife Photo courtesy of Texas Parks and Wildlife DepartmentDepartment
•Scientists discovered that DDT wasScientists discovered that DDT was concentrated in the bald eagle concentrated in the bald eagle
•DDT affected the eagle’s ability to reproduceDDT affected the eagle’s ability to reproduce
Photos courtesy of Texas Parks and Wildlife DepartmentPhotos courtesy of Texas Parks and Wildlife Department
Scientists found thaScientists found that the eagle eggs had t the eagle eggs had thin egg shells and thin egg shells and broke easilybroke easily
Nests contained broNests contained broken, rotten eggsken, rotten eggs
The number of younThe number of young produced per breg produced per breedingedingpair was reducedpair was reduced
Population of adult Population of adult eagles declined to 4,000 eagles declined to 4,000 and the eagle was listed and the eagle was listed as “Endangered”as “Endangered”
Photo courtesy of Texas Parks and Wildlife DepartmentPhoto courtesy of Texas Parks and Wildlife Department
The Environmental Protection Agency (EPA) The Environmental Protection Agency (EPA) banned DDT in 1972 (USA)banned DDT in 1972 (USA)
Photo courtesy of Texas Parks and Wildlife DepartmentPhoto courtesy of Texas Parks and Wildlife Department
Eagle reproduction before and after DDT ban Eagle reproduction before and after DDT ban
Based on: Grier, J., Science, 1982
Eagle populations increased rapidly and Eagle populations increased rapidly and the eagle is now listed as “Threatened”the eagle is now listed as “Threatened”
From: Time, July 11, 1994
Peregrine FalconPeregrine Falcon •Occurred naturallyOccurred naturally over most of continentover most of continental U.S.al U.S.
•Nests on cliffsNests on cliffs
•Keen eyesight Keen eyesight (if human, could read newspap(if human, could read newspaper print at 110 yards)er print at 110 yards)
•Feeds on other birds, kFeeds on other birds, knocking them out of the nocking them out of the sky at 200 m.p.h.sky at 200 m.p.h.
Photo courtesy of Texas Parks and Wildlife DepartmentPhoto courtesy of Texas Parks and Wildlife Department
•After DDT was introducedAfter DDT was introduced in 1940s, DDT weakenedin 1940s, DDT weakened the birds’ egg shells,the birds’ egg shells, devastating the populationdevastating the population
•By early 1970s, the entireBy early 1970s, the entire U.S. population was downU.S. population was down to 12 breeding pairsto 12 breeding pairs
•Peregrines were declaredPeregrines were declared federally endangered andfederally endangered and DDT bannedDDT banned
•Peregrines were bred inPeregrines were bred in captivity and reintroducedcaptivity and reintroduced successfully in citiessuccessfully in cities
DDT & PeregrineDDT & Peregrine
Photos courtesy of Texas Parks and Wildlife DepartmentPhotos courtesy of Texas Parks and Wildlife Department
Prickly pearPrickly 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.