1038 DISEASES AND INSECTS 



DISEASES AND INSECTS 



1307. Imago of a tent-caterpillar. 



ance, but the nymphs gradually acquire the characters 

 and structures of the adult. 



How they eat. To the horticulturist, the mouth- 

 parts of an insect are its most important organs or 

 appendages. The mouth-parts are built on two very 



different plans. 

 Grasshoppers, 

 beetles, cater- 

 pillars and grubs 

 have two pairs of 

 horny jaws, work- 

 ing from side to 

 side, with which 

 they bite or chew 

 off pieces of their 

 food, that then 

 pass into the food- 

 canal for digestion (Fig. 1312). The scale insects (Fig. 

 1313), plant-lice, true bugs (Fig. 1314), mosquitos and 

 others have these jaws drawn out into thread-like organs, 

 which are worked along a groove in a stiff beak or 

 extended under-lip. Such insects can eat only liquid 

 food, which they suck with their beak-like mouth-parts. 

 The insect places its beak on the surface of the plant, 

 forces the thread-like jaws into the tissues, and then 

 begins a sucking operation, which draws the juices of 

 the plant up along the jaws, and the groove in the 

 beak into the food-canal of the insect. Thus a suck- 

 ing insect could not partake of particles of poison 

 sprayed on the surface of a plant. Its mouth-parts are 

 not built for such feeding, and as it is impracticable to 

 poison the juice of the plant, 

 one is forced to fight such 

 insects with a deadly gas, or 

 each individual insect must be 

 actually hit with some insecti- 

 cide. A knowledge of these 

 fundamental facts about the 

 eating habits of insects would 

 have saved much time and 

 money that have been wasted 

 in trying to check the ravages 

 of sucking insects with paris 

 green and similar poisons. 

 Some insects, like the fruit flies, have mouth-parts 

 fitted for lapping up liquids. 



Beneficial insects. 



The horticulturist has many staunch and true friends 

 among the insects. The honey-bee, the many wild 

 bees, and other insects, as they visit the blossoms to 

 get food for themselves, for their young, and honey for 

 man, leave an insurance policy in the shape of tiny 

 grains of pollen, which often insures a crop of fruit 

 that otherwise might be extremely uncertain. The 

 honey-bee is often accused of biting into ripe fruits, 

 especially grapes. They have not 

 yet been proved guilty, and careful, 

 exhaustive experiments have shown 

 that they will not do it under 

 1309 One of the ^ ne mos * favorable circumstances, 

 weevil beetles. With Wasps and other strong-jawed in- 

 a long and strong sects are responsible for most of this 

 proboscis. injury, the bees only sipping the juice 



from the wound. See Bees, Vol. I. 

 Most of the pretty little beetles known to every 

 child as "lady-bugs" eat nothing but injurious insects; 

 many other beetles are also predaceous. Man is also 

 often deeply indebted to many of the two-winged 

 insects or true flies whose larvse live as parasites inside 

 the body of insect pests or feed upon them predaceously. 

 Were it not for the ravenous larvae of the "lady-bugs" 

 and of the syrphus flies, plant-hce of all kinds would 

 soon get beyond control. While man must recognize 

 these little friends as valuable aids in his warfare 

 against the hordes of insect pests, it will rarely be safe 



1308. A beetle. The adult 

 of a borer larva. 



1310. Ground beetle. One of the 

 commonest predaceous insects. 



to wait for the pests to be controlled by their enemies. 

 Fig. 1315 shows a tomato worm bearing the cocoons 

 of a parasite. Fig. 1310 shows one of the predaceous 

 beetles destroying a cutworm. 



Injurious insects. 



There are now several thousand different kinds of 

 insects that may be classed as injurious in the United 

 States and Canada. Over 600 kinds were exhibited at 

 the Columbian Exposition in 1893. All of these may 

 not be injurious every year, as most insect pests have 

 periods of subsidence, when certain factors, possibly 

 their enemies or perhaps climate conditions, hold them 

 in check. The out- 

 look for American 

 horticulturists, so 

 far as injurious in- 

 sects are concerned, 

 is not encouraging. 

 Nowhere else in the 

 world are insects 

 being fought as 

 intelligently, suc- 

 cessfully and scien- 

 tifically as in 

 America, yet we 

 never have exter- 

 minated, and it is 

 very doubtful if we ever will, a single insect pest. 

 This means that American horticulturists will never 

 have any fewer kinds of insects to fight. On the con- 

 trary, there are many more insect pests now than in 

 pur grandfather's early days, and new pests are appear- 

 ing every year. This alarming state of affairs is largely 

 due to two causes, for both of which man is responsible. 

 Man is continually encroaching upon and thereby dis- 

 turbing nature's primitive domain and the equilib- 

 rium which has there become established between 

 animals and plants. In consequence, insects like the 

 Colorado potato beetle, the apple-tree or the peach- 

 tree borers have been attracted from their original 

 wild food-plants to man's cultivated crops, which 

 often offer practically unlimited feeding-grounds. Most 

 of the new insect pests, however, are now coming to 

 America from foreign shores. American horticulturists 

 are continually importing plants from the ends of the 

 earth, and oftentimes the plants are accompanied by 

 one or more of their insect pests. Some comparatively 

 recent introductions of this kind are the sinuate pear- 

 borer, the pear midge, the gypsy moth, the brown-tail 

 moth, the horn-fly and the elm leaf -beetle; such stand- 

 ard pests as the Hessian fly, the cabbage butterfly, the 

 currant-worm, the codlin-moth (Fig. 1296) came in 

 many years ago. Of the seventy-three insects which 

 rank as first-class pests, each of them almost annually 

 causing a loss of hundreds of thousands of dollars, over 







1311. Moths of the peach-tree borer. The lowest one is male. 



