58 REPORT ON INJURIOUS INSECTS FOR 1907. 



The larvae of Beetles possess a well -defined head and biting jaws^ 

 and a pair of jointed legs on the first three segments behind the head 

 (Rose Chafer) or legs are entirely absent (Garden Weevil). 



The larvae of Flies (Diptera) are generally legless and usually 

 the head is merged into the thorax ; some, however, possess pseudo- 

 pods and a head. 



Those of the Hymenoptera (e.g., sawflies, wood wasps, etc.) have 

 six, eighteen, or twenty-two appendages, and in sawfiy larvae the 

 second abdominal segment always has a pair of pseudopods ; in some 

 cases (wood wasps) the limbs are vestigal, while in other cases they are 

 absent. 



The larval stage is usually the one in which the insect does the 

 greatest amount of damage ; they feed voraciously, the daily con- 

 sumption of food often exceeding many times the weight of the larva. 

 With a plentiful supply of food they rapidly increase in size, and, 

 as the chitinous skin is only capable of a limited expansion, it ulti- 

 mately splits, and the larva comes out with a new r , and sometimes 

 differently-coloured skin. This process, known as moulting, usually 

 takes place five times, but the number is variable ; 2, 3, 4, 5, 7, 10, n, 12, 

 and even 20, 25, and 30 moults are known in different insects. The 

 larva is now r said to be full-fed, and it changes to a pupa or chrysalis. 



The duration of the larval period is subject to much variation ; 

 sometimes it is only a few days, w r hile in other cases it may last for 

 months or even years. 



The Pupa. The full-fed larva generally either buries itself in 

 the ground (Rose Chafer), forming a cell of earthy particles, or spins 

 a silky cocoon (Codling Moth), in which it changes to the pupal con- 

 dition. After a time the pupal case containing the insect cracks or 

 splits, and the perfect insect or imago creeps out. 



The Imago. This is the fully-formed insect, and may be de- 

 scribed as an animal consisting of thirteen segments, breathing by 

 tracheal tubes, with a single pair of feelers, and having the body 

 divided up into three distinct regions head, thorax, and abdomen 

 the three segments of the thorax each carrying a pair of jointed legs. 



On reaching the imago stage, the pairing of the sexes is soon 

 effected ; the female then lays her eggs, and shortly afterwards dies, 

 the generation or life-cycle being thus completed. In some cases the 

 perfect insect only lives a few hours or days, but in others they hiber- 

 nate during the winter, and lay their eggs in the following spring. 



Before the depredations of any particular species of insect can be 

 effectively dealt with, it is important that all the stages and variations 

 of the life-cycle should be clearly and thoroughly understood. 



