Edd Hammill, an ecologist at Utah State University, first got an inkling that insecticides might not be having their intendedeffect while conducting research in orange plantations in northern Costa Rica. #A         Hammill and his team surveyed where the mosquitoes were coming from: bromeliads, a group of plants found in warmparts of the Americas, often growing on tree branches. The water-filled spaces between their tightly overlapping leaves host awhole community of insect larvae, including mosquitoes of the species Wyeomyia abebela. #B
     The team looked at bromeliads in plantations—some of which had been treated with insecticides for more than twentyyears—and in untreated forests. The Costa Rican growers use dimethoate to treat their orange trees for plant lice, but it killsmany other insect species too. #C
     Hammill’s team found that despite all the insecticide, the orange plantations were hosting twice as many mosquitoes as thepristine forests. But damselfly larvae—a major predator of larval mosquitoes—were conspicuously missing from theplantations. #D
     When the researchers took the insects into the lab and exposed them to varying levels of dimethoate, they found that theplantation mosquitoes tolerated concentrations ten times higher than the forest mosquitoes. But the plantation damselflies hadevolved no such resistance. #E
     The resistant mosquitoes thus appear to have found a sweet spot: a nursery habitat for their young that is devoid ofpredatory damselflies. There, they flourish.
46. What is the passage mainly about?
(A) Hammill explored how to kill the mosquitoes.
(B) Mosquitoes often grow on branches of bromeliad.
(C) Damselfly larvae increased dramatically.
(D) Mosquitoes are eaten by damselfly larvae.
(E) Pesticides can increase the number of mosquito.