oracle : Bind Variable "a1" is NOT DECLARED for insert

My ruby on rails code is generating the following oracle INSERT query: set define off;

INSERT INTO "MEMBER_ROLES" ("CREATED_AT", "ID", "NAME", "ORG_ID", "UPDATED_AT") VALUES (:a1, :a2, :a3, :a4, :a5)  [["created_at", Tue, 10 Mar 2015 17:32:27 UTC +00:00], ["id", 6], ["name", "test1"], ["org_id", "2"], ["updated_at", Tue, 10 Mar 2015 17:32:27 UTC +00:00]] 

I don't see any error in the console, but when I log into SQL developer I don't see the record being inserted.

Now If i try to manually run the above query in SQL developer i get the following error:

Bind Variable "a1" is NOT DECLARED

0 rows inserted.

This is how the table was created:

CREATE TABLE member_roles 
(
  id  NUMBER primary key,
  name VARCHAR2(200) not NULL,
  org_id VARCHAR2(200) not NULL,
  created_at DATE default sysdate not null,
  updated_at DATE default sysdate not null
)


CREATE SEQUENCE MEMBER_ROLES_SEQ;

set define off;
CREATE OR REPLACE TRIGGER member_roles_bir 
BEFORE INSERT ON MEMBER_ROLES 
FOR EACH ROW

BEGIN
  SELECT MEMBER_ROLES_SEQ.NEXTVAL
  INTO   :new.id
  FROM   dual;
END;

Has anyone else encountered similar issues?