SPECIAL PROBLEMS OF INSECT CONTROL 157 



are leaf-eating sawflies, and many others of less importance 

 are borers and gall insects. 



Currant worm or slug Nematus ventricosus ; pear slug Eriocantpa 

 cerati; rose slug Monostetjia rosce. 



INSECTS ATTACKING ANIMALS: Botfly (ox warble) Hypoderma 

 lineata ; sheep botfly (Estrus oci* ; horse botfly Gastrophilus cqui : 

 horn fly Hcematobia serrata ; screw-worm fly Compsomyia macellariu. 



Beneficial insects. As it is said to " take a thief to catch a 

 thief," so it often takes an insect to catch an insect. From the 

 usual study of injurious forms the impression is likely to be 

 given that almost all insects are injurious. Yet even species 

 which cause considerable damage may perform good service in 

 cross-pollination of plants. The honeybee, our most useful 

 species for this purpose, has the distinct advantage of winter- 

 ing a large force of workers ready to cover the fruit bloom 

 early in the spring, before our native, solitary bees have begun 

 to breed in numbers. 



The problem of the honeybee and fertilization of fruit trees 

 about the home or in the neighborhood is one which may well 

 repay study. The question is, Are there bees enough to do 

 the work ? The stone fruits are said to depend entirely on 

 insect cross-pollination in setting fruit, and if the cherry, plum, 

 and peach trees are not humming at some time during the 

 bloom, there will be little or no fruit. Apples of some varie- 

 ties and most pears are greatly improved in quality when 

 cross-pollinated. 



For at least one hour on a bright, warm day while the trees 

 are in bloom, with watch in hand, time and count the number of 

 blossoms visited by bees per minute. Do this for all the differ- 

 ent kinds of fruit accessible. How many men would it take 

 to do the work of one swarm of bees of fifty thousand workers? 



Are there enough bees to pollinate the flowers and gather 

 the nectar in the neighborhood ? 



Can you find any honeybees working on red clover ? 



