Αν ξεχάσω το σπρέι στο σπίτι, με τσιμπάνε πάντα τα κουνούπια το βράδυ.

Because Greek is talking about a single possible event: if I happen to forget the spray.

• ξεχάσω is the perfective non-past form of ξεχνάω / ξεχνώ.
• After αν in this kind of condition, Greek commonly uses this form.
• It often corresponds to English if I forget.

By contrast, αν ξεχνάω would sound more like if I am in the habit of forgetting or if I keep forgetting, which is not the idea here.

No. Even though it looks like an aorist-related form, here it is not past.

In this sentence, ξεχάσω means something like:

• if I forget
• if I happen to forget

So it refers to a possible event, not to the past. A helpful way to think of it is:

• aorist stem = one whole event
• non-past ending = not past time

Because after αν, Greek does not use να.

Compare:

• να ξεχάσω = that I forget / for me to forget / should forget depending on context
• αν ξεχάσω = if I forget

So αν itself introduces the conditional idea, and να is simply not used there.

Because the second part describes a habitual result or a general truth:

• με τσιμπάνε πάντα τα κουνούπια το βράδυ
• mosquitoes always bite me at night

Greek often uses the present for things that happen regularly. The meaning is:

• whenever that condition happens, this is the usual result

So this is very natural Greek.

Yes, but it would change the feel.

• με τσιμπάνε πάντα = this happens regularly / habitually
• θα με τσιμπήσουν = they will bite me on that occasion

Your sentence uses the present because it emphasizes a repeated pattern, not just one future event.

με means me. It is the weak object pronoun.

So:

• με τσιμπάνε = they bite me

In Greek, these short unstressed object pronouns usually go before the verb:

• με βλέπει = he sees me
• σε ξέρω = I know you
• μας παίρνουν = they pick us up / call us

So με τσιμπάνε is the normal order.

Greek often uses the definite article more than English does.

Here τα κουνούπια means:

• the mosquitoes
• or more naturally in English, just mosquitoes in a general sense

Greek frequently uses the article with:

• subjects
• generic nouns
• things already understood from context

So τα κουνούπια is completely natural, even though English would usually just say mosquitoes.

σπρέι is a loanword from spray. Here it most naturally means bug spray / mosquito spray / repellent spray.

A few useful points:

• το shows it is neuter singular
• σπρέι is commonly used in everyday Greek
• the exact kind of spray is understood from the context with mosquitoes

So το σπρέι here is basically the spray (repellent).

στο σπίτι means at home or in the house/home.

It is a contraction of:

• σε + το σπίτι = στο σπίτι

In this sentence:

• Αν ξεχάσω το σπρέι στο σπίτι
  = If I leave/forget the spray at home

So the phrase tells you where the spray is forgotten.

Greek often uses the article in time expressions.

• το βράδυ = at night / in the evening
• literally, the night/evening, but that literal translation is not how English says it

This is a very common Greek pattern:

• το πρωί = in the morning
• το μεσημέρι = at noon / in the middle of the day
• το απόγευμα = in the afternoon
• το βράδυ = at night / in the evening

So the article is normal here.

Because Greek word order is more flexible than English word order.

The sentence as written:

• Αν ξεχάσω το σπρέι στο σπίτι, με τσιμπάνε πάντα τα κουνούπια το βράδυ.

puts the focus first on the condition, and then gives the result.

The part:

• με τσιμπάνε πάντα τα κουνούπια το βράδυ

is natural Greek, even though English would usually prefer a different order.

You could also say:

• Τα κουνούπια με τσιμπάνε πάντα το βράδυ

and it would still be correct. The difference is mostly one of focus and rhythm, not basic meaning.

Because Greek usually does not need subject pronouns when the verb ending already shows the subject.

• ξεχάσω already means I forget
• so εγώ is unnecessary unless you want emphasis

For example:

• Αν εγώ ξεχάσω... would sound emphatic, like if I forget...
• without εγώ, it is just the normal neutral form

This is very common in Greek.

Both are used.

• τσιμπάνε is very common in everyday spoken Greek
• τσιμπούν is also correct and may sound a bit more formal or careful depending on context

So:

• με τσιμπάνε τα κουνούπια
• με τσιμπούν τα κουνούπια

both mean mosquitoes bite me.

It most naturally describes a repeated situation.

Clues:

• πάντα = always
• τσιμπάνε = present tense for a habitual action
• το βράδυ = a regular time when it happens

So the overall idea is:

• whenever I forget the spray at home, mosquitoes always bite me at night

This is more like a general pattern than a one-time event.

πάντα means always.

It strengthens the idea that this is a repeated, reliable result:

• με τσιμπάνε πάντα τα κουνούπια
• mosquitoes always bite me

Without πάντα, the sentence would still make sense, but it would be less emphatic about how regularly it happens.

Not very naturally. A word-for-word version would be something like:

• If I forget the spray at home, me bite always the mosquitoes at night.

That shows the Greek structure, but it is not good English.

A natural English translation is:

• If I forget the spray at home, mosquitoes always bite me at night.

So it is better to learn the Greek structure as Greek, not force English word order onto it.