EOC Review: Unintended Consequences

With the Biology End of Course Exam less than two weeks away, we used the short Friday class period to work through one of the types of writing prompts that students will need to prepare for.  Students received a writing prompt asking them to brainstorm and then explain two unintended consequences of mosquito eradication to help prevent the spread of malaria.  During the final 10 minutes of class, students shared out their ideas, and their most thoughtful responses are summarized below:

  • Food web disruption – organisms that rely on mosquitoes for food will have less to eat, causing populations of organisms to decline
  • Pollution – soil and local waterways will accumulate large concentrations of insecticides, causing dead zones that affect current and future populations of organisms
  • Off-target effects – the use of an insecticide that kills insects in addition to mosquitoes may negatively affect the food web.  For example, if the insecticide kills insects that pollinate flowers, birds that rely on nectar for food will have less to eat and their populations may decline.
  • Bioaccumulation – the insecticide may be ingested by organisms eating insects killed by the insecticide, causing it to build up to toxic levels in the larger organisms.  Toxicity may prevent reproduction or result in birth defects.
  • Selection for resistant mosquitoes – mosquitoes not killed by the insecticide may carry genetic mutations causing them to be resistant.  Overuse of the insecticide may select for insecticide-resistant mosquitoes which are more efficient at transmitting malaria.
  • Loss of sickle cell allele – humans have co-evolved with malaria, resulting in the preservation of the sickle cell allele in the human population.  Without malaria, the frequency of sickle cell allele may decline, leaving the population at risk should malaria once again return to the area.
  • Over-population – diseases like malaria maintain human populations at a level that may greatly increase in the absence of malaria.  The increased consumption of natural resources by growing populations can have negative effects on the ecosystem.
  • Bad precedent for future generations – the idea that mass killing of an unwanted organism may be short-sighted.  For example, wolves are predators of livestock, and yet most humans value the human-dog relationship.  Given that dogs and wolves share a common ancestor, imagine if mosquitoes represent the common ancestor of a future organism that may be viewed as more favorable to humans.