. Bulletin. Science; Natural history; Natural history. 1 cc^i. Fig. 1 A. Trichostema lanceolatum (camphor weed) flower before the bumble bee (Bombus sonorus) has alighted in quest of nectar. Drawing by Ross Marshall. Fig. IB. T. lanceolatum flowers after the bumble bee has landed. When the bee alights, the weight of its body and the action of its mouth parts in the floral tube cause the anthers and the style to flex rapidly downward, dusting the pollen onto the dorsal surface of the bee's abdomen. Drawing by Ross Marshall. moths would also be able to flex most camphor weed flowers by their wei
. Bulletin. Science; Natural history; Natural history. 1 cc^i. Fig. 1 A. Trichostema lanceolatum (camphor weed) flower before the bumble bee (Bombus sonorus) has alighted in quest of nectar. Drawing by Ross Marshall. Fig. IB. T. lanceolatum flowers after the bumble bee has landed. When the bee alights, the weight of its body and the action of its mouth parts in the floral tube cause the anthers and the style to flex rapidly downward, dusting the pollen onto the dorsal surface of the bee's abdomen. Drawing by Ross Marshall. moths would also be able to flex most camphor weed flowers by their weight on the corolla lobes alone. The two mason bee males collected, however, had weights of only 59 and 53 mg respectively and were thus too light to have tripped many of the flowers tested. Since 23%-81% of the flowers were tripped with 1-2 staples, perhaps some flowers were tripped by weight and other heavier flowers are un- available to mason bee males. An attempt was made to see if a light insect such as these A. urbana males might be triggering the camphor weed flower mechanism by simply thrusting its mouth parts into the curved corolla—thereby mechanically straightening out the S-shaped upper tube. Upon intromission into the corolla tube, each of the following objects would routinely flex the flower tube without any weight on the lower corolla lobes: bristle of "soft" toothbrush, polyolefin bristle of two-inch paint brush, the mouth parts of honey bee heads held with tweezers. Since these objects can be used to flex the flower mechanism, it is possible that the action of insect mouth parts and/or tongues normally plays an important role in this process. It has thus been shown that there is a close relationship between the force required to flex the pollinating apparatus of camphor weed and the actual weight of its key pollinating species. The weight of most of its pollinating insects is slightly greater than the minimum force required to spring the pollinating
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