Chemical and biological control of agricultural pests 5.5

Learning Objectives All students should know: What pests and pesticides are. Most students should know: The features of an efficient pesticide. How biological agents are used to control pests. Some students should know: How integrated pest control systems are managed and what it involves.

Success Criteria All Students: I can match the key terms associated with its definition, by completing the cross word activity correctly. Most students: I know the features of pesticides and how they work to control pests, this was demonstrated by correctly matching the explanations of these specific terms with the cut and stick activity. I can describe and explain how biological agents are used to control pests by correctly answering plenary questions. Some students: I can write a detailed account on, why isn’t the use of the cane toad in Australia a good example of an ‘integrated pest control system’?

Starter Activity Across 7. can not be broken down by micro-organisms. large area of land that contains only one type of species. toxic chemical used to kill pests. toxic chemical used to kill weed. can be broken down into non-toxic substances by micro-organisms. the build up of toxic chemicals. an unwanted organism that interferes with human activity and reduces crop yield.

Starter activity: Answer Across 7. can not be broken down by micro-organisms. Down large area of land that contains only one type of species. toxic chemical used to kill pests. toxic chemical used to kill weed. can be broken down into non-toxic substances by micro-organisms. the build up of toxic chemicals. an unwanted organism that interferes with human activity and reduces crop yield.

Management of Pests Pests are organisms that compete with humans for food sources and space. Controlling pests is important in the agricultural industry. If not treated properly pests will invade our crops, damaging human food sources. There are two main ways to manage pests: Using pesticides (chemical control) Using predators or parasites (biological control)

Chemical Control Pesticides are toxic chemicals that kill pests. Ideally pesticides should be: Selective only kills the species it is supposed to. Biodegradable can be broken down into non toxic substances. It should be non toxic to other organisms Cost effective development cost of pesticides are high and is only useful for a limited period of time as pest will become resistant to it over time. How does this happen? Not accumulate build up of pesticide in specific parts of an organism is not ideal as it will be passed along food chains. Non mobile stays where it is applied.

Bioaccumulation Bioaccumulation can occur where the pesticide is not broken down. Pesticides tend to be fat soluble and accumulates in the environment and in food chains. It builds up in the fatty tissues and can not be excreted as waste product. This problem becomes worse as the pesticide progresses along the food chain. This is because organisms from higher trophic levels will eat large numbers of organisms from the lower trophic level.

Example of Bioaccumulation (1) → → → Some pests not killed, still containing low concentration pesticide Small birds feed on many insects. Building up higher concentrations of pesticide in their fatty tissues. But not toxic enough to kill small bird. Low concentration of pesticide on crop Birds of prey eat many small birds accumulating very high concentrations of pesticides in their fatty tissue. These toxic levels may kill the bird.

Example of Bioaccumulation (2) → → → DDT in zooplankton (0.04 ppm) DDT Insecticide in water (3 x 10-6 ppm) DDT in large fish ( 2ppm) DDT in fish-eating birds (25ppm ) Another example of bioaccumulation is DDT, it was used as an insecticide to kill mosquitoes. But insects slowly became resistant to it. High toxicity of DDT was found in fish which was consumed by birds. As you can see in this food chain the fish has about 10 times more DDT than zooplankton

Biological control Predators and parasites of the pests can also be used to control pests. An example of this could be ladybirds controlling insect pests on citrus fruits. Using a biological control does not eradicate the parasite but controls it, so it is manageable and natural. Ideally the parasite and pests should be in balance with each other. Where the pest has little effect.

Differences between chemical and biological control Chemical control Can have some effect on other non-targeted organisms. Reapplied at intervals  expensive Pests can develop genetic resistance to pesticides overtime. Very specific, chosen predator would only eat the pest. Control organism reproduces itself once it has been introduced therefore cheaper more cost effective. Pests does not become resistance. No pollution

Differences between chemical and biological control Chemical control Very specific, chosen predator would only eat the pest. Can have some effect on other non-targeted organisms. Pests does not become resistance. Pests can develop genetic resistance to pesticides overtime. Control organism reproduces itself once it has been introduced therefore cheaper more cost effective. Reapplied at intervals  expensive No pollution

Integrated pest-control systems These systems include both types of controlling methods to produce a better result for the management of pests. This type of control aims to reduce the effects of pest with minimal impact on the environment. Integrated control involves: The introduction of an organism that is better suited to the local environment and is pest-resistance. Provide suitable habitats for the crops. Monitor crops for signs of pests regularly for earlier prevention. Remove pests when it exceeds the acceptable population level. Use biological agents if necessary If the situation starts to get out of control use pesticide as last resort.

Cane Toad Video You will watch a video on the use of the cane toad as a method of biological control. After the video you will be expected to write the following account: Why shouldn’t the cane toad have been used as an ‘biological control system’ in Australia?

Pest and Productivity Pests often competes with crops for resources. These resources are often related to the rate of photosynthesis, mineral consumption or space. Can you think of any limiting factors of photosynthesis? Pests can also affect the human food source by consuming it themselves, directly competing with humans. Both points above shows how pests interfere with crops to reduce productivity. The overall aim of pest control is to balance the cost and benefits it brings. Farmers often have to think about how to produce cheap food to satisfy their costumers and make profit.

Plenary: Summary Questions Pesticides are used to increase productivity. Explain how their use might sometimes reduce productivity. (3 marks) State two advantages and two disadvantages of biological pest control. (4 marks) Weeds are growing amongst wheat in a field. Explain how these weeds might reduce the productivity of a crop. (3 marks)

Peer Assessment: Answers Pesticides will kill most of the pests-reducing its population. This in turn reduces the population of its predators. (1 mark) However, with no predators controlling pests after pesticide was introduced, the population of pests starts to increase. (1 mark) This could be higher than the pest population before, increasing the effect of pests on the crop – reducing productivity.(1 mark) Advantages: any 2 from: highly specific, targeted only by pest/once introduced it reproduces itself and does not need to be reapplied/pests do not become resistant. (2 marks) Disadvantages: any 2 from: effect id slow as there is a time lag between application and results/ may itself become a pest or may disrupt the ecological balance. (2 marks) 3. Weeds compete with the crop for sources (e.g light, water, mineral ion, space, carbon dioxide..) limiting the supply for crops. (1 mark) This limits the rate of photosynthesis and therefore reduces productivity. (2 marks)

Learning Objectives All students should know: What pests and pesticides are. Most students should know: The features of an efficient pesticide. How biological agents are used to control pests. Some students should be able to: Know how integrated pest control systems are managed and what it involves.

Success Criteria All Students should know: I can match the key terms associated with its definition, by completing the cross word activity correctly. Most students should know: I know the features of pesticides and how they work to control pests, this was demonstrated by correctly matching the explanations of these specific terms with the cut and stick activity. I can describe and explain how biological agents are used to control pests by correctly answering plenary questions. Some students should be able to: Write a detailed account on, why isn’t the use of the cane toad in Australia a good example of an ‘integrated pest control system’?