One of the advantages of Bacillus thuringiensls (B.t.) toxins over che

I have a doubt "often a particular toxin will kill pest species but not affect insets that prey upon the species"- the point after but " not affect insects that prey upon species"---- Here species is pest species?? And if they are pest species than is author saying this in favour of B.T. I.e it is a good thing that insects are not affecting. Than I think "d" is a strengthener not weakener.

Please explain the above.

Thanks in advance.

Hi,

Yes "species" there refers to Pest insect species but in this sentence "not affect insects that prey upon species", the "insects" are the ones (good insects) which eat or kill the pest insect species.

So, if BT toxins don't kill "good insects" then both BT toxins and good insects can kill more pest insect species.

And Option "D" talks about the Pest insects not the "Good insects". That is why if Pest insects get resistant, BT toxins become disadvantageous for future use.

I hope this helps.

(A) Chemical insecticides cause harm to a greater number of insect species than do B.t. toxins. - This advocates for BT, not go against it. Hence, eliminate (A).

(B) No particular B.t. toxin is effective against all insects. - (B) is a bit too extreme. Besides, we are concerned with pest insects and not the entire clan of insects. eliminate (B)

(C) B.t. toxins do not harm weeds that do damage to farm crops. - Though this does look like a good contender, but the argument is all about B.T Toxin and Chemical insecticides. Since we need to stick within the boundary of this passage, (C) will be considered out of scope. Hence, eliminate (C).

(D) Insects build up resistance more readily to B.t. toxins than to chemical insecticides. - This attacks B.T toxin directly. Hence, (D) is the right answer.

(E) Birds and rodents often do greater damage to farm crops than do insects. - irrelevant. Hence, eliminate (E)

One of the advantages of Bacillus thuringiensls (B.t.) toxins over chemical insecticides results from their specificity for pest insects. The toxins have no known detrimental effects on mammals or birds. In addition, the limited range of activity of the toxins toward insects means that often a particular toxin will kill pest species but not affect insets that prey upon the species. This advantage makes B.t. toxins preferable to chemical insecticides for use as components of insect pest management programs.

Which one of the following statements, if true, most weakens the argument?

(A) Chemical insecticides cause harm to a greater number of insect species than do B.t. toxins. - WRONG. Supports the passage rather.

(B) No particular B.t. toxin is effective against all insects. - WRONG. Passage particularly points out about specific species so this choice unnecessarily brings all insects into consideration.

(C) B.t. toxins do not harm weeds that do damage to farm crops. - WRONG. Weed is out of scope of the passage hence irrelevant.

(D) Insects build up resistance more readily to B.t. toxins than to chemical insecticides. - CORRECT. A resistant insect nullify the impact BT has over it the claim made in the passage go weak.

(E) Birds and rodents often do greater damage to farm crops than do insects. - WRONG. Yes, they might be doing but that is not necessary for the argument to hold or fall apart. So, this basically has no impact and it because conclusion is not about who damages crop more but about BT toxins being more preferable.

Answer D.