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 lattmanus 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 
15seconds. ‘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: | 
When Megachile latimanus visits an alfalfa flower, it grasps the 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. Asa 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 flies 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 alfalfa flowers both at Pullman, Wash., and at Arlington 
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 well as at Chico, Cal., and at Arlington 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. 
