ALFALFA SEED PRODUCTION". _ 13 



only about 30 per cent of the flowers visited. No attempt was made 

 to secure records of different species of Bombus, but there is certainly 

 considerable difference in their ability to trip the flowers. The 

 larger bumblebees are clumsy insects and at Chico have been observed 

 to trip with their feet flowers other than the one in which the pro- 

 boscis was inserted. Honeybees trip but few alfalfa flowers, as previ- 

 ously noted by other observers. 



In 1907 a single individual of Megachile latimanus was observed to 

 trip 4 flowers in 30 seconds at Pullman, Wash.; another tripped 12 

 flowers in 70 seconds, and a third tripped 20 flowers in 2 minutes and 

 15 seconds. These three bees tripped flowers at the rate of 9.2 flowers 

 per minute, or 552 flowers per hour. 



The process of tripping is thus described by Evans : 



Wheii Megachile latimanus visits an alfalfa flower, it grasps tlie wings or the keel 

 from below, braces its head up against the standard, and in this way forces the wing 

 and keel petals apart from the standard, so that it can push its head down and reach 

 the honey. As a result, the flower is usually tripped. When this occurs, the pollen 

 is thrown in a miniature cloud that is sometimes visible to the eye. There is abun- 

 dant opportunity for the pollen to lodge upon the head and other parts of the bee, 

 where portions °of it can easily come in contact with the stigma of the next flower 

 that is tripped. Occasionally the proboscis of a bee is caught by the pistil, 

 which after the flower is tripped presses up quite closely to the standard. When 

 thus caught, the bee braces up on all six legs and after one or two vigorous 

 shakes releases itself. Such an accident does not result in any injury to the bee, but 

 merely occasions a short delay. The insect then rubs its proboscis with the 

 two front feet and fUes off to gather honey from other flowers. 



Honeybees were also carefully observed by McKee at Chico, Cal., 

 in 1909. But few flowers were tripped by these insects, though 

 repeated visits seemed to increase the ease of tripping. Thus, one 

 flower tripped after four visits by honeybees; another, after seven 

 visits. In other cases, however, the flowers did not trip even after 

 seven visits by honeybees. 



Short-tongued bees of the genus Andrena have also been observed 

 tripping aMaHa flowers both at PuUman, Wash., and at ArHngton 

 farm, Virginia. 



BUTTERFLIES. 



Various species of butterflies are among the common insect visitors 

 to alfalfa flowers, the most abundant at Pullman, Wash., and Chinook, 

 Mont., being species of Pieris and Eurymus. Several species of 

 butterflies were carefully observed at the two places above mentioned 

 as weU as at Chico, Cal., and at ArUngton farm, Virginia, but in no 

 case was an individual seen to trip a flower. In all cases the butterfly 

 inserts its proboscis at one side of the flower. Our observations on 

 these insects agree fully with those of Urban. 



