60 



back, and they will do the work. As the results of the parasite introduc- 

 tions become better known, and the misstatements and exaggerations with 

 which they have been surrounded are swept away, there will be a revulsion 

 of feeling ; results credited to parasites will be explained in other ways ; the 

 introduced parasites will take the position in our methods of eradicating 

 pests that their services deserve, and will not be extolled as a cure for every 

 ill connected with horticulture. 



Any observant person can follow the rise of insect life in its native 

 land under natural surroundings. For example : A tree becomes so badly 

 infested with scale insects that they form a regular incrustation on the 

 stem and twigs ; then, as with one of our commonest eucalyptus scale 

 insects, Eriococcus coriaceous, we soon find a host of hungry insects taking 

 it in hand. Several of the black ladybird beetles (Rhizobius) devour the 

 scale both in the beetle and larval state ; then, too, the eggs of the 

 pretty little moth Thalpocharis coccopkaga are placed among the scale by 

 the moth, and the resultant larvae not only devour the scale but use up 

 portions of their outer skin to construct the stout cocoons under which they 

 are well protected. Other parasites also are attracted by the abundant food 

 supply, until the twigs are only fringed with ragged bits of scales, and 

 before the season is over the tree is apparently clean and quite recovers its 

 former vitality. If, however, you visit the same bush the following season 

 you will be almost sure to find it more or less infested with the same scale 

 from the survivors of the last year ; it was only the superabundance of scale 

 that had been destroyed ; and the infestation will increase until it again 

 attracts insects looking for food, which again breed up. 



Most of the aphides, that are such pests to roses, peach trees, apples, and 

 other crops, simply swarm and increase so rapidly that one might think they 

 are going to smother the plants infested ; but as soon as they become in this 

 state, the syrphid flies, ladybird beetles, lace wings, and hymenopterous 

 parasites, attracted to their food, take up the work of cleaning the tree. 

 One cannot walk through a vegetable garden on a fine summer day without 

 being struck with the immense numbers of tiny little insects floating about 

 in. the sunshine and hovering over the plants ; most of these, if examined, 

 would prove to be tiny little wasps that are depositing their eggs in the 

 cabbage aphis ; there are thousands and thousands of them busily at work in 

 every cabbage garden in the State where the aphis is in evidence. 



It is a question of cause and effect ; the pest must appear before the 

 parasite or there is no food, and in the forest and uncultivated land this 

 works out its own salvation ; but under the different conditions of the growth 

 of cultivated plants and trees, we cannot afford to wait until they are badly 

 infested. The struggle for existence is quite as an important factor in the 

 insect world as among the larger creatures ; and in this fight for life we find 

 not only that the insects that prey, but also those that are preyed upon, 

 evolve special structures to enable them to escape from their enemies ; just 

 like the case of the battleship being first protected with 9-inch armour 

 plate, and then the cannon being invented that can send a projectile to pierce 

 that 9 inches of plate. Thus a moth produces silk and blends it into a solid 

 mass when it spins its stout cocoon to protect the helpless pupa ; and as a 

 general rule the caterpillars that place their cocoons in the most dangerous 

 exposed places make the stout cocoons, while those that hide in crevices have 

 only a flimsy silken envelope. Jn the same way that section of the coccidse 

 known as mealy bugs are much more easily destroyed than the scale insects 

 like the Lecyniu?n and Aspidiotus, which are closely protected by a thick 

 skin. These s'ructures, so important to the hunted, are circumvented by 



