io6 



to understand the method by which an Insect feeds, 

 whether it be m the larval or adult condition. Almost all 

 remedial measures have to be based upon this factor. We 

 can recognise three methods by vsiiich Insects feed: 'i) 

 By means of the bitmg action of their jaws. [2) By means 

 of sucking, and m this case the mouth organs are mcdihed 

 to form a suctorial apparatus. 3) By iPxeans of a comi- 

 bination of both of these methods. 



Various chemical substances are used for destroying 

 Insects and are known as Insecticides. Bitmg Insects are 

 mainly destroyed by poisoning their food, while sucking 

 Insects can usually only be destroyed by using contact 

 insecticides — those which kill by means of surface contact. 

 This method is adopted for the simple reason that we 

 cannot poison the food when it consists of the internal 

 juices of plants, as is the case with sucking Insects. When 

 using insecticides the grovv^er should proceed with caution 

 until experience has been acquired. Also contact insecti- 

 cides are liable to injure the foliage under certain con- 

 ditions. ]\Iany of the insecticides that have been recom- 

 mended are mefhcient, while others need scientific testing 

 to fully determine their value. Insecticides are artiricial 

 7]iethods of control, but it is necessary to point out that 

 the utilisation of natural methods of control should not be 

 neglected. Natural methods consist in the preservation 

 and increase of those organisms which are directly bene- 

 ficial to man, in that they destroy the injurious forms of 

 animal life. This latter method will be dealt with m a 

 subsequent lecture. 



The first order of Insects that I shall deal with is the 

 Orthoftera, and the only member thereof that concerns us 

 is the common Earwig [Fcrficula aiirtcularia) \ io\. It is 

 a good example of an Insect which undergoes incomplete 

 metamxorphosis. The adult Earwig lays its eggs a 

 group either beneath stones or in the soil. _ During the 

 incubation period she guards the eggs until they hatch, 

 exhibiting in this respect a rudimentary mstance^ of 

 parental care. The young larva=^ are minute white 

 creatures, with very slender forceps and no traces of wings. 

 After they have passed through several moults rudiments 

 of wings' appear, and subsequent growth chiefly consists 

 of an increase in the size of the Insect and the gradual 

 development of the wings. Xo pupa or resting stage is 

 passed through. The Earwig is almost exclusively noc- 



