For Jmuiary. 1923 



11 



Insects and Plants 



WILLARD N. CLUTE 



IT sometimes happens that the gardener, impressed with 

 the visits of butterfles and bees to his flowers, speaks 



of "'beneficial insects," but a more careful considera- 

 tion of the facts might lead him to conclude that there is 

 no such animal. First, last, and all the time, the insect 

 world is absorbed in its own affairs, ever seeking food, 

 shelter, and a place to breed ; always taking what it can 

 and often nearly or quite exterminating the organisms it 

 preys uixjn. And it has always been thus. Although 

 the flowers of the present produce the nectar and pollen 

 utilized by various insects, and in a sense might be said 

 to provide them with food, it is no voluntary act on the 

 part of vegetation. The insect merely takes what it 

 wants ; indeed, it is probable that the activities of the 

 insects are responsible for an increased secretion of nec- 

 tar in flowers, just as man has, by breeding, increased 

 the secretion of milk in cows. 



It is undoubtedly true that our planet began as a flow- 

 erless world, and that when the first insects appeared on 

 it they were obliged, like other forms of animal life, to 

 feed on the plants. Repiesentatives of these early races 

 are still with us in the form of bark beetles, wood-borers 

 and the like. The young or larval stages of the great 

 majority still feed on plant tissues, but the mature insect 

 in higher forms has developed a taste for more refined 

 kinds of food. The first flowers were far from being the 

 showy objects we think of when the word flower is men- 

 tioned. They appear to have been exclusively pollinated 

 bv the wind, and were much like those of the pines, pop- 

 lars, grasses and hazels of the present, which afl^ord no 

 encouragement to nectar-feeding forms. 



Although wind-pollinated flowers do not, as a rule, 

 produce nectar, it is probable that they have always been 

 visited more or less by bees and other insects in search of 

 pollen. .\s a matter of fact, pollen still interests the in- 

 sects, for many flowers that are entirely lacking in nectar 

 are still favorite feeding grounds. The nectar, so com- 

 monly secreted bv flowers, is not exclusively a floral prod- 

 uct. The leaves of many flowering plants also excrete it, 

 notably those of the little partridge pea and the cotton 

 plant, and the outer bracts of the peony are widely noted 

 for this feature among black ant circles. 



The regular secretion of nectar by the floral parts 

 opened an entirely new chapter in plant evolution. With 

 insect visits reasonably certain the plants were assured 

 that their pollen would be carried directly from flower 

 to flower and were thus able to make several changes 

 looking to greater efficiency. Pollen became sticky so 

 that it would adhere to the visitors, and at the same time 

 stamens and carpels became of different lengths, or 

 ripened at different times, in order to prevent self-pollina- 

 tion. With the production of a perianth to protect the 

 nectar and guide the insects to it, fewer stamens were 

 neces'^arv to accomplish pollination and the plant saved 

 in jiollen more than it lost in the production of nectar. 

 Finally the appearance of flowers turned sidewise en- 

 sured that the insect would alight in a definite part of the 

 flower and thus could be covered with pollen by still 

 fewer stamens. Thus the stamen number w^as further 

 reduced until we have whole plant families with but one 

 or two stamens to a blossom and some that manage to 

 carry on business bv means of only half a stamen. 



The accomodating blossoms have provided in numer- 

 ous ways for the storage of nectar until the favorite in- 

 sect calls for it, and have found ways of protecting it 

 from other insects, but even this consideration fails to 



impress the greedy visitors which all too often bite 

 through the walls of the nectary and abstract the sweets 

 without ]iollinating the flower at all. It is small won- 

 der, therefore, that a number of plants with showy flow- 

 ers have other and less conspicuous ones that never open 

 but make use of their own pollen and produce all or most 

 of the seeds. 



^lany species of plants have now become so exactly 

 adapted to the visits of a given insect that they fail to 

 set seeds if it is not present. The absence of an insect 

 from a region, therefore, may limit the distribution of 

 various plants in it. More 'far reaching still, the life of 

 the plant may be so bound up with that of another, 

 through the insect, that the absence of one may limit 

 the other, as in the case of one plant which serves as the 

 ho.st plant to the larval insect that in the mature state 

 pollinates some distant species. 



The more usual way in which insects act to limit the 

 spread of a plant species is by exterminating it in feeding 

 upon it. It is quite likely that the potato plant would 

 be exterminated in regions where the potato-beetle is 

 abundant if man did not constantly fight its enemy. -V 

 redeeming feature of the picture, however, is the fact 

 that the greedy insects are not content to feed exclusively 

 on plants, but have developed a disposition to eat one 

 another. Even man, himself, does not entirelv escape 

 pests of this nature. In numerous instances, however, 

 the safety of the plants lies in this fondness of one insect 

 for another. The ichneumon flies and lady-bugs are f-ver 

 on the search for plant-eating forms, and the dragon-fly 

 is all that his name denotes with reference to niosquitos. 

 In the larval state the dragon-fly larvje eat mosquito 

 larvK, and those that escape and assume the adult form 

 are taken "care of by the grown-up dragon-fly. It seems 

 likely that we shall come to depend more and more on the 

 aid of insects that eat others to protect our plants from 

 harm. 



Looking at the subject as a whole, it seems just retri- 

 bution that overtakes the insect world when the plants 

 turn the tables on them and become the eaters instead of 

 the eaten. The sundew with a dozen leaves like small 

 red hands, lies in wait for its prey and, clutching it, turns 

 its leaves into impromptu stomachs and digests its cap- 

 tives. The pitcher-plants provide little wells within their 

 hollow leaves and calmly drown the insects, in some cases 

 cunningly enticing its victims by sugary secretions with 

 which is mixed a substance that stupifies them. There is 

 a long line of these insectivorous plants — butterworts, 

 catch-flys, bladder worts, Venus' fly-traps and the like, 

 but insects are so numerous and multiply so rapidly that 

 they are not much impressed indeed, certain thrifty speci- 

 mens, eager to capitalize the misfortunes of their fellows, 

 putsh into the pitcher-plant leaves and lay their eggs in 

 the decaving bodies of its victims. 



Doubtless God could have provided us with better fun 

 than hard work, but I don't know what it is. To be born 

 poor is probably the next best thing. The greatest glory 

 that has ever come to me was to be swallowed up in 

 London, not knowing a soul, with no means of subsistence 

 and the fun of A\'orking till the stars went out. To have 

 known any one would have spoilt it. I didn't even know 

 the language. I rang for my boots and they thought I 

 said a glass of water : so I drank the water and worked 

 on. There was no food in the cupboard : so I didn't need 

 to waste time in eating. — Sir James M. Barrie. 



