Biological control of pests: reading answers and analysis
The passage argues that heavy pesticide use has backfired, creating resistant superbugs and the 'treadmill syndrome', as shown by Central American cotton farmers spraying more and more. It presents biological control, using natural enemies of pests, as a cheaper and safer alternative and gives examples from India, Sri Lanka and elsewhere.
The multiple choice (14-17) runs through paragraphs 1, 2, 4 and 5. The YES / NO / NOT GIVEN statements (18-21) cover paragraphs 2, 3 and 7. The sentence endings (22-26) are all in the last two paragraphs, but not in order.
Answer key and self-check
Type what you wrote and hit mark. Hide the key first if you haven't done the passage yet. Every question number jumps to its explanation.
How to attack this block: Q17 repeats 50% in every option, so the test is what the 50% measures. Q16 asks why farmers started, so put the events in time order: they started first and the resistant pests came later.
Question 14
Answer: BParagraph 1, second sentence
What have pesticides contributed to?
Apart from engendering widespread ecological disorders, pesticides have contributed to the emergence of a new breed of chemical-resistant, highly lethal superbugs.
Question says → Passage says
contributed toengendering
an imbalance in many ecologieswidespread ecological disorders
Why: 'Engendering' means causing, and 'widespread ecological disorders' is an imbalance in ecologies in many places. B.
The trap: A borrows 'agroecologists' from paragraph 3, but they name the 'treadmill syndrome'. Nobody reclassifies ecologies. C is the opposite of the passage: pesticides cause disorders, they don't prevent disasters.
Question 15
Answer: AParagraph 2, first sentence
What is true of the 300-plus agricultural pests the FAO counted?
more than 300 species of agricultural pests have developed resistance to a wide range of potent chemicals
Question says → Passage says
no longer responding tohave developed resistance to
most pesticides in usea wide range of potent chemicals
Why: Pests that have 'developed resistance' no longer react to the chemicals that used to kill them. 'A wide range' lines up with 'most pesticides'. A.
The trap: C mixes in the next sentence: about 100 disease-spreading pests are a separate group, not the 300 agricultural ones. B is the opposite of resistance.
Question 16
Answer: DParagraph 4, second sentence
Why did Central American cotton farmers start using pesticides?
the farmers avidly took to pesticides as a sure measure to boost crop yield
Question says → Passage says
began to use pesticidesavidly took to pesticides
to ensure more cotton was harvested from each cropas a sure measure to boost crop yield
Why: 'Boost crop yield' means get a bigger harvest, and 'a sure measure' is a way to ensure it. D.
The trap: B is the main trap. New resistant pests did appear, but in the mid-1950s, a decade after the farmers started spraying in the 1940s. The pests are a result of the pesticides, not the reason for starting.
Question 17
Answer: DParagraph 5, first sentence
What did farmers find about pesticides by the mid-1960s?
necessitating pesticide spraying to such an extent that 50% of the financial outlay on cotton production was accounted for by pesticides
Question says → Passage says
costing 50% of the total amount they spent50% of the financial outlay on cotton production was accounted for by pesticides
Why: 'Financial outlay' is the money spent, and half of it went on pesticides. D.
The trap: All four options use 50%, so you have to read what the figure measures. It's money, not pests killed (A), crops destroyed (B) or new pests (C).
YES / NO / NOT GIVEN
Questions 18-21
How to attack this block: Q18 compares two groups of pests in a way the passage never does. Q20 confuses bio-control with the chemical approach it replaces. Q21 depends on the condition 'when handled by experts'.
Question 18
Answer: NOT GIVENParagraph 2
Do disease-spreading pests react faster to pesticides than farm pests?
Not to be left behind are the disease-spreading pests, about 100 species of which have become immune to a variety of insecticides now in use.
Why: The passage gives the numbers for both groups (300 agricultural, about 100 disease-spreading) that have become resistant. It never compares how quickly either group responds to pesticides. NOT GIVEN.
The trap: 100 is smaller than 300, so some assume disease-spreading pests respond better and answer YES. A smaller count of resistant species says nothing about speed of response.
Question 19
Answer: YESParagraph 3, last sentence
Are some pests now born already immune to certain pesticides?
many pests are known to withstand synthetic chemicals and bear offspring with a built-in resistance to pesticides
Question says → Passage says
a number of pestsmany pests
born with an innate immunitybear offspring with a built-in resistance
Why: 'Built-in resistance' in the offspring is an innate immunity: the young pests have it from birth. YES.
Question 20
Answer: NOParagraph 7, first sentence
Does biological control use synthetic chemicals to change pests' genes?
a more effective and ecologically sound strategy of biological control, involving the selective use of natural enemies of the pest population
Question says → Passage says
biological control entailsbiological control, involving
using synthetic chemicalsthe selective use of natural enemies
Why: Biological control uses natural enemies of the pest, and it's presented as the alternative to synthetic chemicals. The statement describes something it isn't. NO.
The trap: 'Synthetic chemicals' and 'offspring' both appear in paragraph 3, but that's about pesticides and resistance. Bio-control is a different method.
Question 21
Answer: YESParagraph 7, last sentence
Is bio-control safe in some situations?
When handled by experts, bio-control is safe, non-polluting and self-dispersing.
Question says → Passage says
under certain circumstancesWhen handled by experts
free from dangersafe
Why: The condition 'when handled by experts' is the 'certain circumstances', and 'safe' is 'free from danger'. YES.
The trap: 'A new field with limited potential' earlier in the paragraph makes some hesitate. That's about how much it can do, not about whether it's safe.
Sentence endings (A-I)
Questions 22-26
How to attack this block: Each ending is a pest, a crop or a helper, and the sentences pair them up. Work out who eats whom: predators eat insects, insects eat plants, weeds infest fields. The trap in every case is the other living thing in the same sentence.
Question 22
Answer: DParagraph 9, last sentence
What do disapene scale insects feed on?
parasites that prey on 'disapene scale' insects - notorious defoliants of fruit trees in the US and India
Question says → Passage says
feed ondefoliants of
fruit treesfruit trees
Why: A defoliant strips trees of their leaves. These insects are 'notorious defoliants of fruit trees', so they feed on fruit trees. D.
The trap: Parasites are in the same sentence, but they prey on the scale insects. The insects themselves eat the fruit trees.
Question 23
Answer: HParagraph 10, third sentence
What did Neodumetia sangawani eat?
A natural predator indigenous to India, Neodumetia sangawani, was found useful in controlling the Rhodes grass-scale insect that was devouring forage grass
Question says → Passage says
ateA natural predator… was found useful in controlling
grass-scale insectsthe Rhodes grass-scale insect
Why: Neodumetia sangawani is a predator, so it ate the pest: the grass-scale insect. H.
The trap: A, forage grass, is the big trap. The grass-scale insect was 'devouring forage grass'. The predator ate the insect, not the grass.
Question 24
Answer: CParagraph 10, second sentence
What did leaf-mining hispides damage?
when Sri Lanka's flourishing coconut groves were plagued by leaf-mining hispides
Question says → Passage says
blightedwere plagued by
coconut treescoconut groves
Why: A grove is a group of trees, and 'plagued by' means badly damaged by. The hispides attacked coconut trees. C.
The trap: I, larval parasites, appears in the same sentence, but the parasite was the cure, imported from Singapore to control the hispides.
Question 25
Answer: EParagraph 9, second sentence
What might the Argentinian weevil get rid of?
is now trying out an Argentinian weevil for the eradication of water hyacinth, another dangerous weed
Question says → Passage says
may be successfulis now trying out
wiping outthe eradication of
Why: 'Eradication' means wiping out completely, and 'trying out' explains the 'may': it's still being tested. E.
The trap: F, parthenium weed, was controlled by a different weevil, one native to Mexico, in the sentence before. Check which weevil.
Question 26
Answer: BParagraph 10, last two sentences
What does Salvinia molesta infest?
About 30,000 hectares of rice fields in Kerala are infested by this weed.
Question says → Passage says
plaguesare infested by
rice fieldsrice fields
Why: 'This weed' refers back to Salvinia molesta, and it infests 30,000 hectares of rice fields. B.
The trap: G, Brazilian beetles, is in the same part of the paragraph, but the beetle is what cleared the weed from the canal. It isn't plagued by the weed.
300 agricultural pests and about 100 disease pests are resistant, but nothing compares how quickly they respond: NOT GIVEN.
Words from this passage worth keeping
counter-productive(Paragraph 1)
having the opposite effect to the one intended
engendering(Paragraph 1)
causing or producing
potent(Paragraph 2)
powerful, strong
havoc(Paragraph 4)
great damage and disorder
proliferation(Paragraph 4)
rapid increase in number
indiscriminate(Paragraph 7)
done without care or selection
detrimental(Paragraph 7)
harmful
eradication(Paragraph 9)
complete removal or destruction
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The full Cambridge 8 Test 4 reading paper: all three passages, 60 minutes, marked the second you finish with a review of every answer. Already done it? Take it again and see if the same traps still get you.
Cambridge IELTS 8, Test 4, Reading Passage 2. The passage and questions belong to Cambridge University Press and are not reproduced here. We quote short extracts only as evidence for our own commentary, and the answers are published for self-marking. Get the book for the full text, or sit the test on Langujet.
