Los pulgones verdes causan la plaga.

Spanish often uses the definite article el / la / los / las where English does not.

Here, Los pulgones verdes can mean:

• green aphids in general
• or the green aphids if a specific group is already known from context

So Spanish is more comfortable than English with using los for a whole class of things.

The singular is pulgón.

So the pattern is:

• el pulgón = the aphid
• los pulgones = the aphids

Because the singular ends in a consonant, Spanish usually makes it plural by adding -es.

Also notice the accent change:

• pulgón
• pulgones

The written accent disappears in the plural.

In Spanish, adjectives usually come after the noun, especially descriptive ones like colors.

So:

• pulgones verdes = green aphids

This is the normal order. Putting a color adjective before the noun would sound unusual in everyday Spanish.

Because verde is an adjective ending in -e, and adjectives like that usually have the same form for masculine and feminine. They only change for number.

So:

• pulgón verde = singular
• pulgones verdes = plural
• plaga verde = feminine singular
• plagas verdes = feminine plural

The important thing is that the adjective must agree in number with the noun, so here it becomes verdes because pulgones is plural.

Because of agreement.

• pulgones is plural
• plaga is singular

The adjective is verdes, which is plural, so it must go with pulgones.

If the sentence meant that the plague was green, it would be:

• Los pulgones causan la plaga verde

There, verde is singular, so it matches plaga.

Because the subject is plural: Los pulgones verdes.

Spanish verbs must agree with the subject:

• El pulgón verde causa la plaga.
• Los pulgones verdes causan la plaga.

So causan is the third-person plural form of causar in the present tense.

Causan is the present indicative form of causar.

In this sentence, the present tense expresses a general fact or general truth:

• Green aphids cause the infestation

Spanish uses the present tense this way very often for facts, habits, and scientific or general statements.

Spanish often uses the definite article where English might leave it out.

Here, la plaga sounds natural because it refers to the infestation/problem being caused. It can sound like a known or understood result.

Saying causan plaga is possible in some contexts, but it is less natural in a simple sentence like this and can feel more abstract or less specific.

Not always.

In everyday Spanish, especially in gardening, farming, or biology, plaga often means:

• pest infestation
• outbreak of pests
• serious infestation/problem caused by insects or organisms

So in a sentence about aphids, la plaga usually does not mean the historical disease the plague. It usually refers to an infestation or agricultural pest problem.

Yes, but the basic version is the most neutral:

• Los pulgones verdes causan la plaga.

Spanish can change word order for emphasis, for example:

• La plaga la causan los pulgones verdes.

That version emphasizes the infestation first, almost like It’s the green aphids that cause the infestation.

So the original sentence is the most straightforward and neutral way to say it.

A simple pronunciation guide is:

• pulgones ≈ pool-GOH-nes
• verdes ≈ BEHR-des
• causan ≈ KOW-sahn
• plaga ≈ PLAH-gah

A few useful notes:

• In most of Latin America, g in go is a hard g sound, as in go
• v and b are pronounced very similarly in Spanish
• The stress in pulgones is on go
• The stress in plaga is on pla