21. (a) State two roles of nozzles. (b) It is recommended that for tan mixing, a farmer should follow the W.A.L.E.S method. Explain all the necessary steps for a successful tank mixing of pesticide. 22.How might we use pheromones to control insect populations? Provide specific examples in your answer. 23. Explain how biological control can be utilized to control an insect pest. 24. There are two basic ways in which insect pests are controlled i.e. natural and applied control. Discuss two (2) methods under natural and 3 methods under applied control.