Prepared statement insert doesn't work

Question

I have a PHP class to insert POST data in a db. The db has 2 tables: "empleado" and "puesto", where puesto has 2 rows. I want to insert data from a form, but the table "empleado" has a foreign key, so I'm doing a INSERT INTO SELECT as a prepared statement. But when I check the db the table "empleado" is empty...

This is the 1st time I use prepared statements so I don't know if I'm doing it right. Can you tell me what's the problem?

These are the functions of class "Empleado":

public function __construct($host, $usuario, $pass, $db) {

    $this->conexion = new mysqli($host, $usuario, $pass, $db);

}

function nuevoEmpleado($nombre, $puesto, $correo, $pass) {

    $inserta1 = 'INSERT INTO empleado (nombre, idPuesto, correo, password)
                  SELECT ?, idPuesto, ?, ? FROM puesto
                  WHERE puesto = ?';

    if($stmt = $this->conexion->prepare($inserta1)) {

        $stmt->bind_param('ssss', $nombre, $correo, $pass, $puesto);
        $stmt->execute();
        $stmt->close();

    }

}

This file is called "main.php" and here I create an instance:

include('Empleado.class.php');

$empleado = new Empleado('localhost', 'root', 'mysql', 'prueba');

$empleado->listaPuestos();

if(isset($_POST['enviar'])) {

  $empleado->nuevoEmpleado($_POST['nombre'], $_POST['puesto'],, $_POST['correo'], $_POST['pass']);

}

And here's my form:

<form action="main.php" method="post">

    <input type="text" placeholder="Nombre" name="nombre"/>
    <label>Puesto</label>
    <select name="puesto" id="jobs">


    </select>
    <input type="email" placeholder="aaaa@aaa.aaa" name="correo"/>
    <input type="password" placeholder="contraseña" name="pass"/>
    <input type="submit" name="enviar"/>

</form>

The select is populated by an ajax.

Thanks in advance.