In their quest to store food for the winter, harvester ants compete wi

In their quest to store food for the winter, harvester ants compete with squirrels for plant seeds, limiting the growth of Farmville’s squirrels, which are a public health risk since one in 4 squirrels has been found to carry ticks and fleas. However, the red fire ant, which has recently invaded Farmville, has a venomous sting that can cause severe allergic reactions in humans that can result in suffocation and death. Therefore, the planned introduction into Farmville of phorid flies, a natural ant parasite that kills its host by laying eggs into its thorax, would benefit public health, since _______.

(A) phorid flies are not parasitic to ants other than the red fire ant
(B) red fire ants are less effective than many bird species in competing with squirrels for seeds
(C) certain other species of harvester ants are more effective than red fire ants in competing with squirrels for seeds
(D) the sting of red fire ants can also be fatal to squirrels
(E) some pesticides that could be used to control red fire ants are harmful to the environment

in argument we have been told harvester ants indirectly kills squirrel as they compete for seeds...hence squirrels are dying...and we have been also told that ...squirrels cause disease in humans....so in short HARVESTER ANTS ARE SAVING US.
now fire ants are poisonous to humans.....so for that reason...phoroid flies are introduced.....which kills FIRE ANTS...hence again save humans===>so they are benefiting public health.....we have to complete this...
now lets take 2 condition:
1) phoroid flies kills all types of ants...including harvester ants...==>in this case although they are saving us from fire ants...but as flies are also killing harvester ants...we are at more risk to disease caused by squirrels....because their number will increase==>in this case they are not benefiting public health fully

2) if phoroid flies kill only fire ants...then it will benefit public health as harvester ants are still present to take care of squirrels...

and this is what option A says...: phorid flies are not parasitic to ants other than the red fire ant==>it means they are going to kill only fire ants..

hope it helps....