Texas gourd vines unfurl their large, flared.blossoms in the dim hours before sunrise. Until they.close at noon, their yellow petals and mild, squashy.aroma attract bees that gather nectar and shuttle.pollen from flower to flower. But “when you.advertise [to pollinators], you advertise in an.open communication network,” says chemical.ecologist Ian Baldwin of the Max Planck Institute for.Chemical Ecology in Germany. “You attract not just.the good guys, but you also attract the bad guys.” For.a Texas gourd plant, striped cucumber beetles are.among the very bad guys. They chew up pollen and.petals, defecate in the flowers and transmit the.dreaded bacterial wilt disease, an infection that can.reduce an entire plant to a heap of collapsed tissue in.mere days..In one recent study, Nina Theis and Lynn Adler.took on the specific problem of the Texas.gourd—how to attract enough pollinators but not.too many beetles. The Texas gourd vine’s main.pollinators are honey bees and specialized squash.bees, which respond to its floral scent. The aroma.includes 10 compounds, but the most.abundant—and the only one that lures squash bees.into traps—is 1,4-dimethoxybenzene..Intuition suggests that more of that aroma should.be even more appealing to bees. “We have this.assumption that a really fragrant flower is going to.attract a lot of pollinators,” says Theis, a chemical.ecologist at Elms College in Chicopee,.Massachusetts. But, she adds, that idea hasn’t really.been tested—and extra scent could well call in more.beetles, too. To find out, she and Adler planted 168 Texas gourd vines in an Iowa field and,.throughout the August flowering season, made half.the plants more fragrant by tucking.dimethoxybenzene-treated swabs deep inside their.flowers. Each treated flower emitted about 45 times.more fragrance than a normal one; the other half of.the plants got swabs without fragrance..The researchers also wanted to know whether.extra beetles would impose a double cost by both.damaging flowers and deterring bees, which might.not bother to visit (and pollinate) a flower laden with.other insects and their feces. So every half hour.throughout the experiments, the team plucked all the.beetles off of half the fragrance-enhanced flowers and.half the control flowers, allowing bees to respond to.the blossoms with and without interference by.beetles..Finally, they pollinated by hand half of the female.flowers in each of the four combinations of fragrance.and beetles. Hand-pollinated flowers should develop.into fruits with the maximum number of seeds,.providing a benchmark to see whether the.fragrance-related activities of bees and beetles.resulted in reduced pollination..“It was very labor intensive,” says Theis..“We would be out there at four in the morning, three.in the morning, to try and set up before these flowers.open.” As soon as they did, the team spent the next.several hours walking from flower to flower,.observing each for two-minute intervals “and writing.down everything we saw.”.What they saw was double the normal number of.beetles on fragrance-enhanced blossoms..Pollinators, to their surprise, did not prefer the.highly scented flowers. Squash bees were indifferent,.and honey bees visited enhanced flowers less often.than normal ones. Theis thinks the bees were.repelled not by the fragrance itself, but by the.abundance of beetles: The data showed that the more.beetles on a flower, the less likely a honey bee was to.visit it..That added up to less reproduction for.fragrance-enhanced flowers. Gourds that developed.from those blossoms weighed 9 percent less and had,.on average, 20 fewer seeds than those from normal.flowers. Hand pollination didn’t rescue the seed set,.indicating that beetles damaged flowers directly.—regardless of whether they also repelled.pollinators. (Hand pollination did rescue fruit.weight, a hard-to-interpret result that suggests that.lost bee visits did somehow harm fruit development.).The new results provide a reason that Texas gourd.plants never evolved to produce a stronger scent: “If.you really ramp up the odor, you don’t get more.pollinators, but you can really get ripped apart by.your enemies,” says Rob Raguso, a chemical ecologist.at Cornell University who was not involved in the.Texas gourd study.Q: According to the passage, Theis and Adler’s research offersan answer to which of the following questions? Answer Choices: (A)How can Texas gourd plants increase the number of visits they receive from pollinators? (B)Why is there an upper limit on the intensity of the aroma emitted by Texas gourd plants? (C)Why does hand pollination rescue the fruit weight of beetle-infested Texas gourd plants? (D)Why do Texas gourd plants stop producing fragrance attractive to pollinators when beetles are present?
A: Among A through D, the answer is
(A)How can Texas gourd plants increase the number of visits they receive from pollinators?
(B)Why is there an upper limit on the intensity of the aroma emitted by Texas gourd plants?
(C)Why does hand pollination rescue the fruit weight of beetle-infested Texas gourd plants?
(D)Why do Texas gourd plants stop producing fragrance attractive to pollinators when beetles are present?
Answer: 1