110 VEGETABLE GROWING IN NEW SOUTH WALES. 



Insect Pests* 



W. W. FROGGATT, F.L.S., Entomologist, and W. B. GURNEY, Assistant Entomologist. 



Vegetables are attacked by two kinds of insect pests leaf-eating and 

 sap-sucking and growers must know to which of these two classes a par- 

 ticular insect belongs, in order to know what remedy to apply. Insects 

 which eat the leaves have their mouth-parts formed for biting off pieces of 

 vegetable matter, and in this way eat their food in much the same manner 

 as do the higher animals. The insects which suck the plant juices have their 

 mouth-parts formed into a beak, which is inserted into the plant tissues. 

 The most notable amongst insects which chew their food is perhaps the larva 

 of the cabbage moth. These insects can be destroyed by a stomach poison 

 which when taken into the stomach along with the particles of food, kills 

 them.. We apply treatment for this class of insect to the plants, and make 

 no effort to apply it directly to the insects. On the other hand the sucking 

 insects such as aphis, bugs, &c., must be killed by actual contact suffocation 

 and irritation. 



Aphis. 



Small aphides (some winged and some not) make their appearance during 

 the summer months on various plants. At this time they are all females, 

 that have the power of giving birth to their young without the aid of males. 

 The young aphides are born alive and in rapid succession, so that the 

 numbers increase very rapidly. Towards the end of summer winged forms 

 are developed more numerously, and the aphides spread. Winged males are 

 also now developed and fertilise the females, which lay eggs (known as 

 winter eggs) in the soil and decaying vegetation. It is these eggs that 

 enable the aphis to tide the winter over. They hatch in the spring and 

 start the broods of that season. 



The effect of these thousands of tiny insects, each sucking up sap by means 

 of its little beak is to weaken the plant, to reduce its vigour and profit, and 

 even to cause it to wilt. 



Spraying with tobacco or sunlight soap wash, or even a very dilute kerosene 

 and soap wash, as directed on page 130, will keep these pests in check on such 

 crops as peas, beans, cabbage, celery, &c. 



When field crops of such vegetables as turnips are attacked, it is very 

 difficult to spray, and the method of control must be clean cultivation, which 

 kills the winter eggs. By attention to surface cultivation and manuring, 

 healthy plants are raised which are more resistant to attack and less damage 

 will result. 



Fortunately there are an immense number of parasites which live upon 

 and in all kinds of aphis, and they are a great factor in ordinary years in 

 keeping the pest under control. 



