You have been looking at the different types of diseases that affect the human body and the natural defence mechanisms that maintain health. In this last part of the module you will look at how increased understanding has led to the development of a wide range of strategies to prevent and control disease. In this part you will have the opportunity to: • discuss the role of quarantine in preventing the spread of disease and plants and animals into Australia and across regions of Australia.
• explain how one of the following strategies has controlled and/or prevented disease: – public health programs – pesticides – genetic engineering to produce disease resistant plants and animals • perform an investigation to examine plant shoots and leaves and gather first-hand information of evidence of pathogens and insect pests • process and analyse information from secondary sources to evaluate the effectiveness of quarantine in preventing the spread of plant and animal disease into Australia and across regions of Australia.
• gather and process information and use available evidence to discuss the changing methods of dealing with plant and animal diseases, including the shift in emphasis from treatment and control to management or prevention of disease. HSC Biology 9. 4-6 Page 1 Investigating plant diseases As you learned in an earlier Study Guide, many different organisms can cause disease in plants, including bacteria, viruses, fungi, nematodes and insects. All parts of a plant may be attacked, including roots, stems, leaves and flowers.
It is sometimes difficult to identify the causes of plant diseases but black spots caused by fungi are usually easier to identify and viruses may cause leaf deformities or patchy discolouration on leaves or flowers. It is usually easy to identify damage to plants caused by insect attack, too. The edges of leaves may be chewed by caterpillars, there may be white tracks caused by leaf miner insects, or there may be large round swellings of galls caused by wasp larvae. On gum leaves you may see white lerps (the sugary houses of psyllid bugs) or on wattle stems, you may see resin plugs indicating that a borer (witchetty grub) is inside.
Fungi are the most common cause of plant disease. Rusts, rot, mildews, petal blight and black spot are examples of fungal diseases. Viral diseases include rose mosaic virus which results in yellowing of the leaf, or tomato leaf curl virus, which causes the plant to be stunted and the leaves to be rolled inwards. Bacterial diseases of plants include blight, galls and bacterial wilts. Nematodes are roundworms that infect leaves, roots or underground bulbs and tubers. Insect pests include lace bugs that live on the underside of leaves such as azaleas where they suck sap, causing a speckled brown appearance.
Aphids are sap-sucking insects that cause leaves to become distorted. Leaf miners are the larvae of a moth. They burrow through the leaf, leaving behind a silvery trail. HSC Biology 9. 4-6 Page 2 In this activity, you will examine some plants shoots and leaves and record evidence of pathogens and insect attack. Using a hand lens, examine the selection of plant material available. Look for evidence of plant disease (in other words, look for the symptoms of disease) and look for evidence of insect attack. Separate the plants into two groups – those suffering a disease, and those with evidence of insect attack.
Evidence of disease could include discolouration, browning, blotching, swelling, leaf curling, local death of tissue, or even visible mould or powder on the surface of a leaf. Use the photographs or the Internet to help you identify the pathogen. Record your observations in the table below and, if necessary, use the Internet to find the scientific, binomial name of the pathogen. Examine more closely the plants showing evidence of insect attack. Describe the damage that you observe and suggest what type of insect was responsible.
Record your results in the table. HSC Biology 9. 4-6 Page 3 Results: Pathogen or insect pest, including its binomial name Plant name Description of evidence of pathogen or pest HSC Biology 9. 4-6 Page 4 What is quarantine? The protection of Australia from the entry of unwanted pests and diseases of animals and plants is essential for the wellbeing of us all. It is the task of the Australian Quarantine and Inspection Service (AQIS) to provide this protection, together with the community. Australia is a protected place. It is important that it remain so.
Its isolation from the world’s largest land masses has meant that in the days before air travel and international trade on a grand scale it was easier than it is today to keep out many unwanted pests and diseases. Quarantine aims to protect Australia and Australians against the entry of unwanted exotic pests and diseases. Exotic pests and diseases are those which come from any country outside Australia. The scope of the problem Each year close to eight million passengers and about 20 million tonnes of cargo pass through quarantine on arrival at Australian airports and seaports.
Each year about 160 million items of international mail enter Australia and may contain items subject to quarantine. All of these arrivals pose a risk for human health, our agricultural industries and the natural environment. People bring with them their personal belongings, gifts and souvenirs. Any of these items could carry hidden pests and diseases. So too could the cargoes of animals, plants, foodstuffs and other items which are important for our trade with overseas countries HSC Biology 9. 4-6 Page 5 Forty days The word quarantine comes from the Latin quaranti giorni, meaning ’40 days’.
Forty days was the time given to isolating ships that carried disease. When they came into port those on board the ships had to stay in quarantine and were not allowed ashore until 40 days had passed. It was generally accepted that 40 days would be enough time for the disease to be treated and for its infectious stage to pass. All ships under quarantine had to fly a yellow flag. The risk increases During the voyage of the Second Fleet to Australia, infectious diseases, poor diet and unhygienic conditions caused the deaths of a quarter of the passengers.
Of the thousand who sailed from England, only 750 landed at Sydney Cove, many of them helplessly ill. During the voyage of the Third Fleet one in ten people died. The First Fleet took 250 days to travel from England to Australia. Today a flight from England to Australia takes about 24 hours. Travel-time between Asian countries and the Americas to Australia is much less. Shorter travelling time means that there is no 40-day quarantine period on journeys to Australia. Every year close to eight million passengers pass through Australian seaports and airports, making quarantine surveillance more important than ever before in Australia’s history.
This is an age when strict rules of hygiene apply to international carriers, and compulsory immunisation against common infectious diseases is a fact of life in some countries. HSC Biology 9. 4-6 Page 6 Prohibited items Many countries have pests and diseases such as foot and mouth disease of cattle or rabies, which have disastrous effects upon animals and plants. Australia is fortunate because so far we have managed to keep most of these pests and diseases out of Australia. Pests and diseases can be carried into Australia by people, animals, animal products such as meat, plants, plant products such as timber, and in soil on machinery.
All of these must undergo quarantine inspections, and plants and animals must be isolated at quarantine stations. The time spent in quarantine means that any pest or disease can be isolated and prevented from spreading. A prohibited item is one which is forbidden by law, because it is a quarantine risk. Types of quarantine Quarantine works in a number of different ways in Australia – border controls look after the clearance of passengers and cargo into Australia, while animal, plant and human quarantine look at the scientific risks of particular pests and diseases and what actions need to be taken to prevent them coming to Australia.
Border control Border controls are carried out at checkpoints at airports, seaports, and some mail exchanges. Passenger clearance and cargo clearance are the two types of quarantine control at the main entry points into Australia. Quarantine HSC Biology 9. 4-6 Page 7 officers use a range of techniques including computers, detector dogs, X-ray machines, surveillance, scientific support and visual inspection at international airports, seaports, mail exchanges and container depots. Animal quarantine Animal quarantine applies to all kinds of animals from insects, fish and birds to larger animals.
Animals coming into Australia must spend time at specially equipped quarantine stations to ensure that they are free of disease before being allowed into the country. Plant quarantine All plants or parts of plants such as fruits, seeds, cuttings, bulbs and corms, as well as things made from wood or bamboo, must be examined and if necessary, treated by Quarantine officers. Live plants, cuttings, bulbs and corms must be kept at plant quarantine stations, or testing stations if seeds, to make sure they’re not carrying pests or diseases.
Human quarantine Quarantine officers monitor reports about the health status of passengers arriving in Australia by aircraft and shipping vessels to ensure that they are not suffering from diseases like yellow fever. A number of infectious diseases can be spread to other people by insects such as mosquitoes and if allowed to get into Australia would be very difficult to eradicate. All international airports in Australia have in place a surveillance monitoring program to ensure that known insect carriers of human disease are quickly detected and destroyed. HSC Biology 9. 4-6.
Quarantine case study – preventing the spread of animal and plant disease into Australia Foot and mouth disease is caused by a virus. Australia is free of foot and mouth disease and we want to keep it that way. It is a major quarantine risk. Early records show that foot and mouth disease may have been introduced into Australia four times between 1800 and 1872. Each time the disease was eradicated. How could it affect Australia? Controlling foot and mouth disease is not easy. An outbreak could spread quickly. Wild or feral animals which roam across Australia would spread the disease.
An outbreak of the disease would cost billions of dollars worth of damage to our beef, mutton, dairy and wool industries, which are big earners for Australia in overseas markets. These markets would be closed to us. All animals in infected areas would have to be killed, then burnt and buried. How is the disease spread? The virus which spreads foot and mouth disease travels through the air. It affects only cloven-hooved animals. A cloven hoof is one that is divided into two or more parts. Cloven-hooved animals include cattle, pigs, goats and camels.
Once the virus becomes established it can spread the disease through a herd of cattle in as little as 48 hours. HSC Biology 9. 4-6 Page 9 What does the disease look like? During the early stages of the disease blisters appear mainly on the mouth, or in the case of pigs on the snout, tongues, lips and between the claws of the hooves and on the feet. These soon burst leaving a raw, painful surface. In cows, milk production drops. Consequences of outbreak It is difficult for people not in rural Australia to imagine the consequences for all Australians in the event of an outbreak.
No matter where it occurred it would cause an immediate closure, by other countries, of our export markets for all livestock, meat and dairy produce. The overall cost of lost markets and rural production is estimated to be $6000 million plus $8 million for each day the outbreak lasts. Major markets such as the USA would not be regained until at least 12 months after the outbreak ended. Whenever the disease is identified, an immediate, predetermined slaughter-out plan will take place. All cattle, sheep, pigs and goats in the immediate area will be killed, then burnt or buried.
Commonwealth and State funds will compensate the owners, but what sum could make true amends to a grazier for the sudden loss of a pedigree herd? A quarantine area around the infected property would be determined and declared by the agriculture authorities. Police would control traffic movements. Race meetings and agricultural shows would be postponed and saleyards and abattoirs closed for a period. The greatest long-term disaster would occur if feral cattle, pigs, camels or goats in the outback became a permanent source of this dreaded virus. HSC Biology 9.
4-6 Page 10 Quarantine precautions The foot and mouth disease can be carried into Australia by live animals, in meat products like salami and sausages, in dairy food, on farm clothes, animal hair, farm footwear and clothing, soil, bones, untreated hides, car tyres and other equipment. It can also survive chilling, freezing and freeze-drying. That is why it is important that people are completely honest when they fill in the declaration form before coming into Australia. If they have any of these items in their luggage they should show them to a Quarantine officer.
Some of the items may be treated and later returned. Others, because of the danger they represent, may have to be destroyed. Distribution of foot and mouth disease HSC Biology 9. 4-6 Page 11 Has quarantine been effective at preventing the introduction of foot and mouth disease? Give reasons for your answer? HSC Biology 9. 4-6 Page 12 Read the following article about citrus greening disease, a disease of citrus fruit that is currently absent from Australia. Citrus greening disease destroys Indonesian production.
By Sarina Locke from Canberra , ACT Friday, 24/04/2009 Citrus trees are dying in Indonesia. The cause is citrus greening disease, a bacteria spread by insects. Australia is in real danger of catching the bug, with scientists suggesting it might blow on the wind, or fly in with a tourist. Australia’s biosecurity protection is one of the reasons our country has the massive commitment to aid in Indonesia. Citrus greening disease has already spread in the US, most recently into the orchards of South Carolina.
On the populous island of Java, farmers should now be harvesting their small mandarins called jeruk but most trees have been pulled or are diseased. Citrus greening or Huanlongbing as it’s known in Asia was first found in the 1950s on one of the Indonesian islands, but its rapid spread over the past 10 years has surprised researchers at Gadja Mada University. It’s a bacterium is spread by the psyllid insect and it destroys the phloem cells, the veins that carry sugar and nutrients throughout the plant, leaving the fruit barely edible.
“The fruit becomes abnormal, and more sour and hard,” says Dr Siti Subandiyah, the Indonesian project leader on the Australian Centre for International Agricultural Research, (ACIAR) project based at Gadja Mada University in Jogjarkarta. Within just a few years the tree dies and there is no cure, so prevention is the main course of action being taken by the extension staff. Huanglongbing disease is also destroying citrus in Vietnam, so the ACIAR project has partners in Vietnam too.
Meanwhile Australia should be on alert for the psyllid insect carrying the bacteria- which could devastate citrus production in Australia too. HSC Biology 9. 4-6 Page 13 A case study – Quarantine and the spread of plant and animal diseases within Australia South Australia grows approximately 42 per cent of the annual Australian vine crop and produces more wine than all other States combined. One reason for South Australia’s viticultural success is that grape phylloxera (pronounced fil-er-a), the worst insect enemy of grape vines, has never been introduced into the State.
Since 1899, quarantine regulations have forbidden the introduction of any part of a vine into South Australia. Quarantine of grapes, grapevines and grape rootstock is necessary to protect Australia’s wine and dried fruit industry from grape phylloxera. Grape phylloxera exists in most of the grape growing areas of the world. It does not occur in most grape growing areas of Australia.
Phylloxera appeared in France in 1869, and within 30 years destroyed 75 per cent of the vineyards of this most important wine-producing country. By 1919, people carrying.\ infested parts of grape vines to ‘clean’ areas had spread phylloxera to most wine-growing countries in the world, including the eastern States of Australia. Only Chile and Cyprus and two Australian States – South Australian and Western Australia – continue to grow European vines in soil that is free of phylloxera.
Travellers carrying grapes or parts of vines could easily cause an outbreak of grape phylloxera in South Australia or Western Australia or re-infest other grape growing areas in Australia where phylloxera has previously been eradicated.
An outbreak of grape phylloxera in the early 1900s in areas of Victoria and New South Wales caused widespread damage to the Australian grape industry. HSC Biology 9. 4-6 Page 14 It’s an aphid Grape phylloxera is an aphid or plant louse. It is native to the eastern States of North America. Over the centuries, American vines have developed a resistance to it. Wherever phylloxera has appeared, European vines have been grafted on to the resistant American rootstocks. The tiny insects are too small to be seen without a microscope.
They have a soft body and a tube-like mouth that they use to suck the sap of vine roots. This sucking causes hard round swellings, called galls, to form on the vine roots. A few months later, the galls decay, damaging, stunting and eventually killing the vine roots. A fertile aphid The reproductive power of the species is almost impossible to imagine. It has been reported that the offspring in one season from one egg may total 40,000 million aphids. Aphids may be present in soil clinging to vehicle wheels, footwear, cultivating equipment, picking boxes and, most likely of all, vine roots.
Residents of South Australia visiting interstate vineyards should take care not to transport phylloxera back into South Australia. With the benefits of continuous research into grape growing, the South Australia Phylloxera Board has kept grape growers aware of phylloxera and its disastrous consequences should it ever be introduced. Not only would whole vine-growing areas be wiped out but it would also affect South Australia’s dried vine fruit industry and wine industry, currently a major export earner for the State. HSC Biology 9. 4-6 Page 15
Quarantine precautions Overseas travellers should never bring grapes or any parts of vines into Australia. The only safe method of introducing plant and vine material is through AQIS. The movement of grapes, grapevines and cuttings between the States and Northern Territory is either very restricted or, in most cases, prohibited. There are also restrictions on the interstate movement of various other fruit, vegetables and plant material designed to prevent the spread of pests and diseases to ‘clean’ areas. Has quarantine been entirely successful in preventing the entry of grape phylloxera into Australia?
Has quarantine within Australia been successful? When equine flu entered Australia in 2007, infected horses were found in New South Wales and in Queensland. Quarantine measures were enacted to prevent the transport of horses to regions that were free of equine flu. Equipment was disinfected, horse racing events were cancelled and animals at risk were vaccinated to prevent the disease from spreading. Because of the measures put in place, Victoria remained free of equine flu and there has not been another outbreak. HSC Biology 9. 4-6 Page 16.
Evaluate the effectiveness of quarantine The greatest quarantine risks are plants, plant products, animals, animal products and soils. All items that pose a quarantine risk can carry hidden plant or animal diseases. At airports or shipping terminals, as well as at mail centres, prohibited goods are intercepted by AQIS. Quarantine checking stations are also set up across both State and agricultural region borders to intercept produce that may be a quarantine risk. The table below shows interceptions of goods and personal effects entering Australia, 1996 – 1998.
Year 1996 1997 1998 Interceptions 5121 10 952 15 060 What do these figures suggest about the effectiveness of our quarantine service? Is it likely that all prohibited goods were intercepted? Suggest some reasons why quarantine would fail to intercept all prohibited goods. HSC Biology 9. 4-6 Page 17 To evaluate the effectiveness of quarantine in preventing the spread of plant and animal diseases into Australia or across regions of Australia, you firstly need to decide on criteria on which to base your judgement. What information do you need before you can make a judgement about the effectiveness of quarantine?
You will need to show ways that the Australian Quarantine Inspection Service (AQIS) has successfully prevented the introduction or spread of diseases, and examples of failure. Identify examples of quarantine successes in preventing the entry of plant and animal diseases into Australia. Identify examples of quarantine successes in preventing the spread of plant and animal diseases across regions of Australia. Identify examples of quarantine failures in Australia. Read the article from the World Health Organization (www. who. int/csr/don/2004_01_15/en/) HSC Biology 9.
4-6 Page 18 Avian Influenza The disease in birds: impact and control measures Avian influenza is an infectious disease of birds caused by type A strains of the influenza virus. The disease, which was first identified in Italy more than 100 years ago, occurs worldwide. All birds are thought to be susceptible to infection with avian influenza, though some species are more resistant to infection than others. Infection causes a wide spectrum of symptoms in birds, ranging from mild illness to a highly contagious and rapidly fatal disease resulting in severe epidemics.
The latter is known as “highly pathogenic avian influenza”. This form is characterized by sudden onset, severe illness, and rapid death, with a mortality that can approach 100%. Migratory waterfowl – most notably wild ducks – are the natural reservoir of avian influenza viruses, and these birds are also the most resistant to infection. Domestic poultry, including chickens and turkeys, are particularly susceptible to epidemics of rapidly fatal influenza. Direct or indirect contact of domestic flocks with wild migratory waterfowl has been implicated as a frequent cause of epidemics.
Live bird markets have also played an important role in the spread of epidemics. Recent research has shown that viruses of low pathogenicity can, after circulation for sometimes short periods in a poultry population, mutate into highly pathogenic viruses. During a 1983-1984 epidemic in the United States of America, the H5N2 virus initially caused low mortality, but within six months became highly pathogenic, with a mortality approaching 90%. Control of the outbreak required destruction of more than 17 million birds at a cost of nearly US$65 million.
During a 1999-2001 epidemic in Italy, the H7N1 virus, initially of low pathogenicity, mutated within 9 months to a highly pathogenic form. More than 13 million birds died or were destroyed. HSC Biology 9. 4-6 Page 19 The quarantining of infected farms and destruction of infected or potentially exposed flocks are standard control measures aimed at preventing spread to other farms and eventual establishment of the virus in a country’s poultry population. Apart from being highly contagious, avian influenza viruses are readily transmitted from farm to farm by mechanical means, such as by contaminated equipment, vehicles, feed, cages, or clothing.
Highly pathogenic viruses can survive for long periods in the environment, especially when temperatures are low. Stringent sanitary measures on farms can, however, confer some degree of protection. Could migratory birds carry avian influenza to Australia? Explain What impact would this have on the effectiveness of Australian quarantine control? Use all of the previous information to make a judgement of the effectiveness of quarantine in preventing the spread of diseases into Australia OR across regions of Australia. Give reasons for your decision.
(Hint: Using a plant and an animal disease example, describe the quarantine measures in place, explain how these measures assist in preventing the spread of disease into Australia or across regions of Australia, and, make a judgement about the effectiveness of the quarantine measure, which can be supported by data on the occurrence and spread of the disease. ) HSC Biology 9. 4-6 Page 20 Strategies for disease control and prevention There are several strategies for the control of preventable diseases. These include vaccination and quarantine.
Three other strategies are public health programs, pesticides, and genetic engineering to produce disease resistant plants and animals. We will briefly look at all three of these, but concentrate on one, public health programs. Public health programs Public health programs provide sanitation, safe drinking water, immunisation programs and even the quarantine of disease sufferers entering the country. These have all played a part in disease control. You may accept a safe water supply as a fact of life, but that has not always been the case in Australia and certainly is not the case in many other countries.
One of the first things aid agencies try to establish when working in these countries is a safe water supply. A classic epidemiological study was performed by English physician John Snow. He found that people who suffered from cholera in the 1849 London epidemic lived mostly in the area of the Broad Street pump. Water was collected daily from village pumps or wells. Snow found that nearly every person with the disease had consumed water from the Broad street pump. He had the pump closed and no further outbreaks occurred in the area.
HSC Biology 9. 4-6 Page 21 Read the article “The Development of Public Health” and answer the questions below. Compare the age of death in Leeds with the age of death in a country area in 1842. What were living conditions in Leeds like in 1842? What were the main causes of death in Leeds? How are these diseases spread? Cholera and typhus epidemics in Leeds prompted some improvement. What was the government response? The Public Health Act in 1875 compelled Councils to improve what? What diseases were reduced as a result?
How do improvements in housing reduce the incidence of tuberculosis? How do vaccination programs reduce the incidence of disease? HSC Biology 9. 4-6 Page 22 Modern public health programs Because you have probably seen TV advertisements showing the gruesome effects of smoking, sun exposure and alcohol you may be aware that health programs have been set up in NSW to prevent and control human disease. While pathogens are not implicated in non-infectious diseases, health strategies also target these diseases and aim to reduce their incidence.
Methods used by NSW Health include public education such as advertisements about the health effects of alcohol, smoking (remember the ‘Quit’ campaign) and of having unprotected (without a condom) sex; mass immunization procedures such as for MMR (measles, mumps, Rubella) or Human Papilloma virus in schools; screening for high blood pressure, cervical cancer and breast cancer (BreastScreen NSW provides free mammograms to those over 50); and laws requiring that certain diseases such as HIV/AIDS are notifiable (there are penalties for not notifying public health units within 24 hours) or that people with other diseases such as rubella and chicken pox must be isolated. The table below shows some examples of notifiable diseases.
To be notified by doctors HIV/AIDS Food poisoning (two or more cases) Gastroenteritis (in educational or residential institutions) Measles TB To be notified by laboratories Anthrax Giardiasis Hepatitis Malaria Influenza Rubella To be notified by hospitals Cholera Legionnaire’s disease Meningococcal disease Poliomyelitis Rabies Tetanus To be notified by school principals Diphtheria Measles Mumps Pertussis Poliomyelitis Rubella HSC Biology 9. 4-6 Page 23 Compulsory notification ensures early detection of these diseases so that strategies can be put in place to control the spread of the disease. Government regulations ensure that garbage is collected and disposed of correctly, sewage is removed and treated and water supplies are protected.
Government regulations also ensure that safe procedures are in place for the handling, storage and preparation of food and for disease control in hospitals. Identify a public health strategy and explain how it can control or prevent disease. HSC Biology 9. 4-6 Page 24 Pesticides Pests are organisms that affect the normal growth of a plant or animal. For example, the cotton bollworm is a pest that can devastate a cotton crop, and ticks are pests that can affect the health and growth of cattle. Mosquitoes are pests because they can transmit diseases like malaria. Agricultural pests can be controlled by the use of pesticides or by biological control. Pesticides include insecticides that kill insects, fungicides that kill fungi, and herbicides that kill weeds.
Because pests can kill or stunt food plants, the use of pesticides has been critical in contributing to the quality and quantity of food production. Since they are cheap, pesticides have been the preferred method of pest control but there have been serious environmental problems associated with the use of pesticides. Some long-term effects include: • Pests have evolved resistance to some pesticides • Non-target organisms are killed • Toxic residues accumulate in food chains • Farm workers can be poisoned by contact with pesticides Pesticides have been important in killing disease vectors, such as mosquitoes. You will remember the earlier section of work on malaria and how the malarial parasite, Plasmodium is transmitted by mosquitos.
Malaria can be controlled by spraying with pesticides to kill mosquitos. Adult mosquitoes are killed by pesticides such as DDT or dieldrin. Beginning in 1956, the World Health Organisation began a campaign using DDT for mosquito control in malarial areas. This campaign successfully controlled malaria in Sri Lanka and other areas of the world but did not eliminate it globally. DDT resistant mosquitoes are now a problem in many areas. Insecticide-treated bed nets, which can reduce the transmission of malaria by 17% are cheap and effective ways to prevent people from getting malaria, but only 4% of Africa’s children sleep under one each night. HSC Biology 9. 4-6 Page 25.
Biological control has been an effective alternative to the use of pesticides in some situations. Genetic engineering Genetic engineering is the purposeful manipulation of genetic material to alter the characteristics of an organism. Genetic engineering (and plant breeding) has been used to develop crops that are resistant to certain diseases. Rust resistance in wheat is an example of breeding being used to develop disease resistance. Genes from the bacteria Bacillus thuringiensis has been genetically engineered into cotton plants to eliminate the need for spraying for cotton bollworm caterpillar, Heliothis. Many predator insects feed on Heliothis caterpillars, so spraying with insecticides is not ideal.
The Bt genes that produce the toxin responsible for caterpillar death have also been introduced into tomatoes, corn and potatoes. In Australia Bt cotton was the first genetically engineered crop grown. Cattle ticks cause significant economic loss because heavy infestation by ticks reduces the growth rate of cattle and ticks can also cause disease. Ticks are normally controlled by dipping the cattle in baths of pesticide, but these are toxic and can remain in meat. Genetic engineering has now been used to produce an anti-tick vaccine for cattle. Insulin produced by recombinant DNA technology and is another example of a strategy to fight disease by genetic engineering. HSC Biology 9. 4-6 Page 26 Read the Scientific American article “Seeds of Concern” abou.