The accent mark shows where the stress goes: pul-GÓN.
Without the accent, normal Spanish stress rules would make you stress it differently. The written accent tells you the final syllable is stressed.
So it is pronounced roughly:
This is also useful because many Spanish learners might otherwise guess PUL-gon, which would be incorrect.
In most of Spain today, ll is usually pronounced the same as y. This is called yeísmo.
So tallo is commonly pronounced roughly like:
However, pronunciation varies by region. In older or more conservative pronunciation, ll could sound slightly different, but for most learners of modern Spain Spanish, pronouncing it like y is normal and understood.
Spanish en often covers both in and on, depending on context.
So:
Even though English distinguishes in and on, Spanish often uses en for both.
En el tallo is the most natural choice here.
With something attached to or situated on part of a plant, en el tallo sounds natural and idiomatic.
So while sobre is possible in some contexts, en el tallo is what a learner should expect and use here.
The personal a is usually used before specific human beings, and sometimes pets or personified animals.
Examples:
But with a non-person object like un pulgón, you normally do not use a:
So Vi a un pulgón would not be the normal form here.
Yes, but the meaning changes slightly.
So el tallo is definite because the speaker likely means the stem of the plant being discussed or observed.
The usual and most natural order is:
This follows a common pattern:
You could change the order for emphasis, for example:
That is still correct, but it sounds more marked, as if emphasizing where the aphid was.
For a learner, the original order is the safest and most natural one.
It is close, but it should be pronounced in a Spanish way, with a short, clean vowel:
In most varieties of Spanish, b and v are pronounced very similarly, so vi does not sound like the strong English v in all contexts.
The important part for learners is:
So just say it simply as vi.
Yes. Pulgón is the usual word for aphid, the small plant-eating insect often found on stems and leaves.
This matters because Spanish is being quite precise here:
So the sentence is not just saying I saw a bug on the stem; it is specifically an aphid.