This would neither strengthen nor weaken the official’s argument. He restricts his conclusion to “certain” fruits, so it would not affect his argument if peaches did worse than pears.

This would neither strengthen nor weaken the official’s argument. He makes no claim about the effectiveness of the new pesticide when used in tandem with the old pesticide.

This strengthens the official’s argument. It implies pear trees treated with the new pesticide showed more resistance to insects than those treated with the old pesticide during the same time.

This is irrelevant to the official’s argument. He makes no claim about the ability of untreated trees to keep their fruits safe from insects.

This slightly weakens the official’s argument—it doesn’t strengthen it. It suggests factors specific to District 10 could have been responsible for fewer pears being eaten by insects.