yuugata ni naru to, ka ga ooku naru node, musiyoke wo tukaimasu.

In 夕方になる, に marks the state that something changes into.

So 夕方になる means it becomes evening or it gets to be evening.

This is different from 夕方に meaning simply in the evening as a time expression. Here, because it is followed by なる, the idea is a change into evening.

Verb dictionary form + と often means when or whenever, especially when one thing naturally leads to another.

So 夕方になると means:

• when it becomes evening
• whenever evening comes

It has a regular, predictable feeling: evening comes, and then the next thing happens.

Both can mean when, but the nuance is different.

• 〜と often sounds like a natural consequence or repeated pattern.
• 〜たら is more flexible and can be used for one-time events too.

So this sentence with 〜と sounds like a general pattern:

• When it gets to be evening, mosquitoes become numerous...

That fits the idea of something that regularly happens.

Yes, because 〜と is not directly connecting to 使います.

The structure is:

• 夕方になると、蚊が多くなる
• ので、虫よけを使います

So 〜と connects evening comes with mosquitoes become numerous, which is a natural result. Then ので gives the reason for using repellent.

That makes the sentence perfectly natural.

They are the same verb, but used in two different places:

• 夕方になる = it becomes evening
• 多くなる = it becomes many / more numerous

So the sentence uses なる twice because it describes two changes:

1. the time changes into evening
2. the number of mosquitoes increases

With 多い, the thing that is numerous is usually marked by が.

So:

• 蚊が多い = there are many mosquitoes
• 蚊が多くなる = mosquitoes become numerous

You could use は in some contexts for contrast or topic marking, but が is the most neutral and natural choice here.

多い is an い-adjective. When an い-adjective is used before なる, it changes to the 〜く form.

So:

• 多い → 多くなる
• 暑い → 暑くなる
• 寒い → 寒くなる

That is why the sentence says 蚊が多くなる.

It means there come to be a lot of mosquitoes or mosquitoes become more numerous.

In natural English, you would usually not say mosquitoes become many, but in Japanese this is a normal way to describe an increase in their presence or number.

Both are possible, but the nuance is slightly different.

• 蚊が多いので = because there are a lot of mosquitoes
• 蚊が多くなるので = because mosquitoes become numerous / start getting numerous

The version with 多くなる matches 夕方になると very well, because both parts describe a change:

• it becomes evening
• mosquitoes become numerous

So it gives the sentence a nice cause-and-effect flow.

ので means because.

Compared with から, ので often sounds:

• a little softer
• more explanatory
• more matter-of-fact

So:

• 蚊が多くなるので、虫よけを使います = Because mosquitoes become numerous, I use bug repellent

If you used から, it would still be correct, but slightly more direct.

虫よけ means bug repellent or insect repellent.

It is made from:

• 虫 = insect / bug
• よけ = protection against / keeping away

It is also often written as 虫除け.

In this sentence, it most naturally means something like mosquito repellent, spray, lotion, or another product used to keep bugs away.

Because 使う means to use, and the thing being used is its direct object.

So:

• 虫よけを使います = use bug repellent

This is a very standard object + を + verb pattern.

The Japanese non-past form is used not only for the future, but also for:

• habits
• repeated actions
• general truths

So 使います here means something like:

• I use bug repellent
• I usually use bug repellent
• I will use bug repellent when that happens

In this sentence, it sounds most like a habitual or general action.

The subject is omitted, which is very common in Japanese.

From context, English often supplies I:

• I use bug repellent

But depending on context, it could also mean:

• we use bug repellent
• people use bug repellent

Japanese often leaves out subjects when they are understood.

No. Standard Japanese is normally written without spaces:

夕方になると、蚊が多くなるので、虫よけを使います。

The spaces are usually added only in learning materials to make the sentence easier to read.