FERTILIZATION IN PIMA COTTON. 37 



Various Hymenoptera are the most efficient carriers of cotton 

 pollen at Sacaton, Ariz., 20 as is probably the case wherever cotton is 

 grown. The honeybee and wild bees (Melissodes spp.) are the most 

 important cotton pollinators in this locality. 



The honeybee (Apis mettifica L.) is very assiduous in its visits 

 to cotton flowers, although sometimes preferring the extrafloral 

 nectaries to those within the flower. 21 Nevertheless, this insect prob- 

 ably holds, first rank at Sacaton, Ariz., as a conveyor of cotton pollen, 

 especially among Pima flowers. As was noted on a preceding page, 

 honeybees entering and emerging from the flowers when the petals 

 are just beginning to unfold almost invariably come in contact witli 

 the reproductive organs. Later in the morning, when a sufficient 

 aperture has developed, the bees usually crawl down the inside of the 

 petals without touching the stigmas or stamens and make their exit 

 in the same manner. 22 Occasionally, however, the honeybee touches 

 the staminal column and stigmas even when the corolla is fully open, 

 this being especially likely to happen when the insect is confused by 

 the entrance of another individual. 



At times wild bees of the genus Melissodes (M. agilis agilis Cress., 

 M. agilis aurigenia Cress., M. tristis Ckll.) are even more efficient 

 pollinators than honeybees. It was observed at Sacaton, Ariz., in 

 1921 that Melissodes were much more numerous in the cotton fields 

 toward the close of the season than was the case earlier in the sum- 

 mer and that, unlike the honeybee they commonly crawl over the 

 stigmas and staminal column of open flowers in order to reach the 

 nectaries at the base of the corolla. Another bee, Megachile parallela 

 Smith, is remarkable for the quantity of pollen it carries but is 

 apparently a much less frequent visitor. 



Large wasps of the genus Campsomeris, especially G. dives Pro v., 

 also frequent the cotton flowers. They apparently prefer upland 

 varieties, which have a shallow, widely flaring corolla, to the 

 Egyptian cotton with its deep and relatively narrow corolla. These 

 insects carry much pollen from flower to flower. Their habits of 

 grasping the stamens with their legs when entering and leaving 

 the flower and of pressing the stamens against the stigmas while 

 drinking from the intrafloral nectaries doubtless also contribute 

 materially to self-pollination. 



Other Hymenoptera which have been observed to carry cotton 

 pollen at Sacaton, Ariz., are Cerceris sp., Dasymutilla Ursula Cress., 

 and the carpenter bees (Xylocopa arizonensis Cress, and X. vari- 

 puncta Patt.) 23 A species of Pepsis seems to be more efficient in dis- 

 tributing pollen within the flower than in transferring pollen from 

 one flower to another. 



20 Allard states (2, p. 254) that in northern Georgia Melissodes binuzoulata Le P. and 

 the honeybee are " the most abundant and constant visitors of cotton." Allard gives a 

 list of insects observed to visit cotton flowers in that region, with interesting notes on 

 the itineraries of honeybees and bumblebees among the cotton plants. In a later paper 

 by the same author it is stated (3, p. 680) that of 129 observed entrances of insects into 

 cotton flowers in the Georgia locality, 45 were by species of Melissodes and 45 by honey- 

 bees. It was noted that the wild bees were much the most frequent visitors when the 

 observations began, while later the honeybees increased the frequency of their visits. 



21 Seasonal variations in the habit of the honeybee in this respect were noted by Allard 

 in Georgia (2, pp. 256, 257). 



22 The same habit was observed at Palestine, Tex., by Shoemaker (1,3). 



33 According to Shoemaker US) bumblebees were the most active pollinators at Pales- 

 tine, Tex., in September, but seemed to be more efficient in insuring thorough self-polli- 

 nation than in effecting cross-pollination. 



