250 



ANALYSIS OF THE ENVIRONMENT 



may be neatly combined, as in the honey- 

 bee. The bees, in which the pecuUar nec- 

 tar-pollen food supply (i.e., a "balanced ra- 

 tion') is carried over to the larvae, con- 

 trast sharply in this respect with the moths 

 and butterflies. These in tlieir adult flower- 

 visiting stage have completed their growth 

 and can fulfill their energy needs by the 

 carbohydrate nectar alone. The group be- 

 havior of honeybees that leads them to ex- 

 ploit a single type of flower at a time ob- 

 viously tends to extreme efficiency of cross 

 pollination (von Frisch, 1923). 



It may be pointed out that insect visitors 

 are abundant at the male flowers of many 

 wind-polHnated plants, feeding on the vast 

 excess of pollen, but that in dicHnous plants 

 of this type they do not exhibit the sHghtest 

 tendency to visit the female flowers (Do- 

 flein, p. 93). 



The short adult Ufe of many moths and 

 butterflies makes it possible for them to 

 develop close adjustment of an individual 

 species to the short blooming season of a 

 particular flower. Resting places for the 

 slow-moving butterflies appear to be devel- 

 oped in numerous types of day-blooming 

 flowers, but are less frequent among the 

 night flowers visited by the whirring moths. 



An extreme of adjustment between spe- 

 cific species of plant and specific animal vis- 

 itor is presented by the extraordinary length 

 of the nectar-bearing lobe in certain tropi- 

 cal orchids, which is matched by the length 

 of the tongue in the attendant sphingid 

 moth. The extreme length of 250 mm. is 

 reached in the Madagascan Macrosilia clu- 

 entius (Doflein, p. 109). 



To summarize the flower environment of 

 insects: A rich food supply is ofiEered in the 

 form of nectar and excess pollen by the ma- 

 jority of flowering plants, and the animal 

 exploitation of these foods is accomplished 

 by specific and exact adjustments, not only 

 to the securing of the food, but quite cer- 

 tainly for the development of pollen-trans- 

 ferring devices. Double and reciprocal evo- 

 lution of plants and animals has led to ex- 

 tremes of evolutionary adjustment. That the 

 attraction of the flowers for the insects is in 

 the service of the plant-species for cross 

 polhnation is shown by the occasional in- 

 stances in which the lure for the insects con- 

 sists of smell only, with no counter benefits 

 of food supplied. The familiar instance of 

 the poUen-and-nectar-feeding bees exhibits 

 complete adjustment of the whole animal 



throughout its fife history to the balanced 

 diet offered, and stiongly indicates that the 

 social evolution of the honey bee was pro- 

 foundly influenced by the nature of the 

 food supply. 



The majority of insects adjusted to nectar 

 or pollen feeding or both belong to the 

 orders Lepidoptera and Hymenoptera and 

 these types function especially in cross pol- 

 lination. Pollen-feeding beetles present httle 

 adjustment either to the special food or to 

 the function of cross pollination (except for 

 the fuzzy coats of certain flower visiting 

 beetles). The Diptera have evolved an illu- 

 minating series of graded adjustments for 

 nectar-and-poUen feeding and for cross pol- 

 hnation. The excrement-and-carrion feeding 

 flies are also exploited by certain flowers by 

 means of the development of corresponding 

 bad odors. The elaborate tropical swan 

 flower (Aristolochia grandiflora) is a nota- 

 ble example of a "carrion flower." 



Extremely close obhgate adjustment be- 

 tween insect and pollinated flower, extend- 

 ing beyond the provision of pollen and nec- 

 tar as food for the visiting insect, is exhib- 

 ited by the chalcidoid wasps that fertihze 

 the various species of figs. A species of 

 Blastophaga, for example, is essential to the 

 commercial production of the familiar culti- 

 vated Smyrna fig. These wasps develop in a 

 special series of pistillate flowers referred to 

 as "gall flowers;" the complex life history of 

 the insect, with wingless males and winged 

 females, is accurately adjusted to the devel- 

 opment of the successive staminate and fer- 

 tile pistillate flowers of the fig. Thus a series 

 of flowers is sacrificed by the plant in its 

 rigidly specific association with an insect 

 predator-pollinator. 



The reciprocal adjustments of the yuccas 

 of southwestern North America and a tin- 

 aeid moth, the yucca moth, are less com- 

 plex, but involve equally specific adjustment 

 of the moth in both structure and behavior. 

 The moth has a special pollen-gathering ap- 

 paratus on its maxillae, into which it ac- 

 tively packs a ball of sticky pollen. The 

 moth subsequently turns to egg laying, 

 pierces the wall of the yucca ovary with its 

 ovipositor, and deposits an egg within; after 

 each egg is deposited, the moth climbs to 

 the top of the pistil and rubs part of the 

 sticky pollen into the open end of the stig- 

 matic tubes. About six eggs are laid, and 

 each requires developing fertiUzed ovules 

 for its growth; but there is a large excess of 



