Biological Control + Agents

Question 1

how can whiteflies in a greenhouse full of tomato plants be controlled?

Answer 1

by introducing a tiny parasitic wasp called Encarsia - these lay their eggs inside the larvae of the flies, which hatch and then eat the larvae and so reduce the numbers of whitefly

Question 2

does biological control fully eradicate a pest?

Answer 2

no - it never does as if the organism killed of all the pests then it too would die from lack of food

Question 3

what is the aim of biological control?

Answer 3

to reduce pest numbers to a level where they no longer cause significant economic damage

Question 4

what is the effect of introducing a natural predator?

Answer 4

ladybirds can be used to control the populations of aphids in orange groves

Question 5

what is the effect of introducing a herbivore?

Answer 5

herbivore (e.g. moth) eat pest plant such as prickly pear cactus in Australia

Question 6

what is the effect of introducing a parasite?

Answer 6

wasp encarsia lays its eggs in whitefly eggs and reduces the population

Question 7

what is the effect of introducing a pathogenic microorganism?

Answer 7

a fall in pest numbers - such as that caused by the myxomatosis virus on rabbit population in Australia

Question 8

what is the effect of introducing sterile males?

Answer 8

mate with females but produce no offspring, so pest numbers fall

Question 9

what is the effect of using pheromones?

Answer 9

sex hormones released to attract males or females which are then collected and destroyed, reducing the reproductive potential of the population

Question 10

what are the advantages of pesticides?

Answer 10

• reduces pest population instantly
• can kill the whole population of pests

Question 11

what are the disadvantages of pesticides?

Answer 11

• cost (need for regular applications)
• not specific e.g. will kill predaceous insects and pollinating insects in addition to the pest
• pest can become resistant to chemical
• chemical can concentrate in all organisms higher up the food chain

Question 12

what are the advantages of biological control?

Answer 12

• organism only introduced once as it will reproduce
• only one cost for the initial introduction
• pest specific - only kills the pest
• pest will not become resistant
• no effect on other animals in the food chain

Question 13

what are the disadvantages of biological control?

Answer 13

• takes time to reduce pest population
• not all population killed
• expensive if re-populating is required