Learn Turkish: Yağmurda sivrisinekler bile mahvoldu. - Even the mosquitoes were ruined in the rain.

In Turkish, the emphatic particle bile (even) always comes immediately after the word or noun phrase it emphasizes. Since the sentence emphasizes 'even the mosquitoes', bile must directly follow sivrisinekler.

The subject is plural (sivrisinekler), so why is the verb singular (mahvoldu) instead of plural (mahvoldular)?

In Turkish, when the subject of a sentence is a plural non-human entity (like animals, objects, or ideas), the verb generally remains in the singular form. Since mosquitoes are animals, the verb stays as the singular mahvoldu.

Is sivrisinek a compound word?

Yes! It is made up of the words sivri (sharp or pointed) and sinek (fly). So a mosquito is literally described as a 'sharp fly' in Turkish, which then takes the plural suffix -ler here to become sivrisinekler.

I recognize the ending of mahvoldu. Does it come from the helper verb olmak, and why is it written as one combined word?

Spot on. It is a combination of the noun mahiv (ruin or destruction) and the helper verb olmak (to be or become). When they combine, the letter 'i' in mahiv drops out. Because a vowel is lost during the combination, Turkish grammar rules require the two words to be merged into one: mahvoldu.