How can I use a select alias into a derived table (which is inside CASE When clause)?

Question

I intend to use a value from my main select into a derived table (which is inside a WHERE THEN clause SQL). This is my query: P.S.: I need to change the value 207 to plague

SELECT DISTINCT(`inspectionpointregisters`.`plague_idplague`) AS `plague`,
(SELECT `plaguecropformulalist`.`formula_idformula`
FROM `zagros_content`.`plaguecropformulalist` AS `plaguecropformulalist`
WHERE `plaguecropformulalist`.`plague_idplague`=`plague`
AND `plaguecropformulalist`.`crop_idcrop`={0}
AND `plaguecropformulalist`.`active`=1) AS `formula_plg_crp`,
CASE WHEN (SELECT `formula_plg_crp`) = 5 THEN
    (SELECT MAX(`plaguestage`) FROM
        (SELECT DISTINCT `inspectionpointregisters`.`plaguestage_idplaguestage` AS `plaguestage`
        FROM `zagros_content`.`inspectionpointregisters` AS `inspectionpointregisters`
        WHERE `inspectionpointregisters`.`inspectionpoints_idinspectionpoints`
        IN
            (SELECT `inspectionpoints`.`idinspectionpoints`
            FROM `zagros_content`.`inspectionpoints` AS `inspectionpoints`
            WHERE `inspectionpoints`.`inspection_idinspection`=404)
        AND `inspectionpointregisters`.`plague_idplague`=207) AS `derived_table`)
ELSE
    (SELECT (0)) END AS `plg_index_1`
FROM
    `zagros_content`.`inspectionpointregisters` AS `inspectionpointregisters`
WHERE
    `inspectionpointregisters`.`inspectionpoints_idinspectionpoints`
IN
    (SELECT `inspectionpoints`.`idinspectionpoints`
    FROM `zagros_content`.`inspectionpoints` AS `inspectionpoints`
    WHERE `inspectionpoints`.`inspection_idinspection`=404)