SECURITIES EXCHANGE COMMISSION
                              Washington, DC 20549

                                  SCHEDULE 13G

                    Under the Securities Exchange Act of 1934
                                (Amendment No. )

                        WESCO INTERNATIONAL INCORPORATED
                                (Name of Issuer)

                                  Common Stock
                         (Title of Class of Securities)

                                    95082P105
                                 (CUSIP Number)


                                December 31, 2009
              Date of Event Which Requires Filing of this Statement


                 Check the appropriate box to designate the rule
                    pursuant to which this Schedule is filed

                                [X] Rule 13d-1(b)
                                [ ] Rule 13d-1(c)
                                [ ] Rule 13d-1(d)


 

1) Name of Reporting Person: Pioneer Global Asset Management S.p.A. (PGAM)


2)   Check the Appropriate Box      (a)
     of A Member of  Group
     (See Instructions)              (b)

3)   SEC Use Only

4)   Citizenship of Place of
     Organization                             Italy

         Number of                                   (5)Sole Voting
         Shares                                      Power          0
         Beneficially Owned
         by Each Reporting
         Person With                                 (6)Shared Voting
                                                      Power           2,704,458
                                                      [See Item 4 below.]

                                                     (7)Sole Disposi-
                                                      tive Power      0


                                                     (8)Shared Disposi-
                                                     tive Power       2,704,458
                                                     [See Item 4 below.]

9)   Aggregate Amount Beneficially     2,704,458
     Owned by Each                   [See Item 4 below.]
     Reporting Person

10)   Check if the aggregate Amount in Row (9) Exclude Certain Shares (See
      Instructions)

11)   Percent of Class Represented
      By Amount in Row 9.                     6.0%

12)   Type of Reporting
      Person (See Instructions)               FI





1) Name of Reporting Person: Pioneer Investment Management, Inc. (PIM)

2)   Check the Appropriate Box     (a)
     of A Member of  Group
     (See Instructions)            (b)

3)    SEC Use Only

4)    Citizenship of Place of
      Organization                            Delaware

         Number of                                     (5)Sole Voting
         Shares                                                 Power     0
         Beneficially Owned
         by Each Reporting
         Person With                                   (6)Shared Voting
                                                       Power          2,576,491
                                                       [See Item 4 below.]

                                                       (7)Sole Disposi-
                                                        tive Power        0


                                                      (8)Shared Disposi-
                                                      tive Power      2,576,491
                                                      [See Item 4 below.]

9)   Aggregate Amount Beneficially    2,576,491
     Owned by Each                  [See Item 4 below.]
     Reporting Person

10)  Check if the aggregate Amount in Row (9) Exclude Certain Shares (See
     Instructions)

11)  Percent of Class Represented
     By Amount in Row 9.                     5.7%

12)   Type of Reporting
      Person (See Instructions)               IA



Item 1(a)         Name of Issuer.

                            WESCO INTERNATIONAL INCORPORATED


Item 1(b)         Address of Issuer's Principal Executive Offices:

                  Commerce Court
                  4 Station Square
                  Suite 700
                  Pittsburgh, PA 15219
                  United States

Item 2(a)         Name of Person Filing:

                  PGAM and PIM

Item 2(b)  Address of Principal Business Office:

           The principal business office for PGAM is:
           Galleria San Carlo 6
           Milan, Italy

           The principal business office for PIM is:
           60 State Street
           Boston, MA 02109

Item 2(c)  Citizenship:

           PGAM is organized under the laws of Italy.

           PIM is a corporation organized under the laws of the
           State of Delaware.

Item 2(d)         Title of Class of Securities:

                  Common Stock

Item 2(e)         Cusip Number:

                  95082P105

Item 3   The person filing this statement pursuant to Rule 13d-1(b)
         or 13d-2(b) is:

             PGAM is a parent holding company or control
             person in accordance with Section 240.13d-1(b)(1)(ii)(J).

             PIM is an investment adviser in accordance with Section
             240.13d-1(b)(1)(ii)(E).


Item 4.  Ownership.

(a) Amount Beneficially Owned:**

        PGAM: 2,704,458
        PIM:  2,576,491

(b) Percent of Class:

        PGAM: 6.0%
        PIM:  5.7%


(c) Number of shares as to which such person has

         (i) sole power to vote or to direct the vote: 0

         (ii) shared power to vote or to direct vote:**

        PGAM: 2,704,458
        PIM:  2,576,491

         (iii) sole power to dispose or to direct disposition of: 0

         (iv) shared power to dispose or to direct disposition:**

        PGAM: 2,704,458
        PIM:  2,576,491

**Shares reported on this Schedule 13G (the Shares) are owned by (i) collective
investment vehicles (Funds) advised by PIM and (ii) Funds advised by other
advisors that are direct or indirect wholly-owned subsidiaries of PGAM
(Additional PGAM Subsidiaries).  In their roles as investment manager or
adviser to the Funds, PIM and the Additional PGAM Subsidiaries possess
investment and/or voting control over the Shares.

PIM is a direct  subsidiary of PGAM. PGAM is a limited liability company and the
holding company  incorporating  all of the Pioneer  Investments asset management
business   (including  PIM,  and  the  Additional  PGAM  Subsidiaries)  and  may
therefore, be deemed to beneficially own the Shares.

PGAM, PIM, and the Additional PGAM Subsidiaries disclaim beneficial ownership of
the Shares except to the extent or their respective pecuniary interests therein,
if any.  The filing of this  Schedule 13G shall not be construed as an admission
that the Reporting Persons are the beneficial owners of the Shares for any other
purposes than Section 13(d) of the Securities Exchange Act of 1934.

In  accordance  with  Securities  and Exchange  Commission  Release  No.34-39538
(January 12, 1998) (the"Release"),  this filing reflects the securities that may
be deemed to be beneficially owned by the Reporting Persons,  each of which is a
directly or indirectly owned subsidiary of Unicredit S.p.A. ("Unicredit").  This
filing does not reflect securities,  if any,  beneficially owned by Unicredit or
any other  subsidiaries of Unicredit whose ownership is disaggregated  from that
of the Reporting Persons in accordance with the Release.

Item 5.  Ownership of Five Percent or Less of a Class.

If this statement is being filed to report the fact that as of the date Hereof
the reporting person has ceased to be the beneficial owner of more than five
percent of the class of securities, check here:

Item 6. Ownership of More than Five Percent on Behalf of Another Person.

Various  persons have the right to receive or the power to direct the receipt of
dividends  from,  or the  proceeds  from the sale of, the Common  Stock of WESCO
INTERNATIONAL INCORPORATED. The interest of one person, PIM, in the common stock
of WESCO INTERNATIONAL INCORPORATED, amounted to 2,576,491 shares or 5.7% of the
total outstanding Common Stock at December 31, 2009.

Item 7.  Identification and Classification of the Subsidiary Which Acquired
         the Security Being Reported On By the Parent Holding Company.

         See Item 4.

Item 8.  Identification and Classification of Members of the Group.

         Inapplicable.

Item 9.  Notice of Dissolution of the Group.

         Inapplicable.

Item 10. Certification.

     By signing  below I certify  that,  to the best of my knowledge and belief,
the  securities  referred to above were  acquired  and are held in the  ordinary
course of business  and were not acquired and are not held for the purpose of or
with the effect of  changing  or  influencing  the  control of the issuer of the
securities  and were not  acquired and are not held in  connection  with or as a
participant in any transaction having that purpose or effect.

    By  signing  below PGAM  certifies  that to the best of its  knowledge  and
belief, the foreign regulatory scheme applicable to it as a sub-holding  company
for the asset  management  division in the UniCredit  Banking Group,  the latter
being  regulated  by the  Bank of Italy  and the  Commissione  Nazionale  per le
Societa`e la Borsa  (CONSOB),  is  substantially  comparable  to the  regulatory
scheme applicable to the functionally equivalent U.S. institution(s).  PGAM also
undertakes to furnish to the Commission  staff,  upon request,  information that
would otherwise be disclosed in a Schedule 13D.

SIGNATURE

     After  reasonable  inquiry and to the best of my  knowledge  and belief,  I
certify that the information  set forth in this statement is true,  complete and
correct.


                  Date: February 16, 2010

                  Pioneer Global Asset Management S.p.A




                  By: /s/ Roger Yates
                  Name:   Roger Yates
                  Title:  CEO; Head of Asset Management Division


                  Pioneer Investment Management, Inc.




                  By: /s/ Teri W. Anderholm
                  Name:   Teri W. Anderholm
                  Title:  Chief Compliance Officer





                                     EXHIBIT

                             JOINT FILING AGREEMENT

In accordance with Rule 13d-1(k)(1) promulgated under the Securities Exchange
Act of 1934, the undersigned agree to the joint filing of a Statement on
Schedule 13G (including any and all amendments thereto) with respect to the
Common Stock of WESCO INTERNATIONAL INCORPORATED and further
agree to the filing of this agreement as an Exhibit thereto. Each party to
this Agreement expressly authorizes each other party to this Agreement to
file on its behalf any and all amendments to such Statement on Schedule 13G.

Date: February 16, 2010

Pioneer Global Asset Management S.p.A




By: /s/ Roger Yates
Name:   Roger Yates
Title:  CEO; Head of Asset Management Division



Pioneer Investment Management, Inc.




By: /s/ Teri W. Anderholm
Name:   Teri W. Anderholm
Title:  Chief Compliance Officer