The differences among species of crop plants are irrelevant to this argument, which is suggesting a strategy for crop plants in general. This doesn't strengthen Peter's argument.

This doesn't strengthen Peter's argument. It just tells us that according to Peter, industrialized nations probably have higher than necessary rates of crop damage from insects. We're not interested in how industrialized countries handle their crops, we're looking to strengthen the connection between insects' preference for leaves of abundantly watered plants and Peter's suggested strategy to reduce risk of crop damage.

This strengthens Peter's argument, because it tells us that whatever risks come with mild drought stress, those risks are less of a problem than insect damage. So the trade-off between the two risks that Peter is suggesting makes sense.

This isn't relevant for Peter's argument, which is about the overall strategy farmers should adopt with respect to their crops. The fact that sometimes other factors get in the way doesn't strengthen or weaken Peter's suggestion.

Remember that Peter tells us in one of the premises that insects are more likely to feed on abundantly watered plants. Since we don't directly contradict premises on the LSAT, we have to assume Mexican bean beetles are an exception and are unlike most other insects. Either way, this answer choice would weaken the argument, if anything, and certainly doesn't strengthen it.