Erro ComboBox Cannot find bean under name

// erro
javax.servlet.jsp.JspException: Cannot find bean under name listaMarcas

// meu codigo html
<html:form action="Action?method=inicio">
	Selecione uma Marca do Carro
	<html:select property="idMarca" styleId="idMarca">
		<html:option value="" styleId="idMarca">
			Marca
		</html:option>
		<html:options collection="listaMarcas" name="MarcaModelo" property="nomeMarca" labelName="nomeMarca" />
	</html:select>
</html:form>

//meu struts config
<struts-config>
	<form-beans>
		<form-bean name="MarcaModelo" type="br.MarcaModelo"></form-bean>
	</form-beans>
	
	<action-mappings>
		<action path="/Action" type="br.Action" parameter="method" name="MarcaModelo" input="/index.jsp" scope="session">
			<forward name="retorno" path="/index.jsp"/>
		</action>
	</action-mappings>
</struts-config>

// minha action
	public ActionForward inicio(ActionMapping mapping, ActionForm form,
			HttpServletRequest request, HttpServletResponse response)throws Exception {

		MarcaModelo marcaModelo = (MarcaModelo) form;
		MarcaDao marcaDao = new MarcaDao();
		List<MarcaModelo> listaMarcas = marcaDao.RecuperarMarcas();
		request.setAttribute("listaMarcas", listaMarcas);

		return mapping.findForward("retorno");
	}

//meu form
private String idModelo;
private String nomeModelo;
private String idMarca;
private String nomeMarca;
private List<MarcaModelo> listaMarca;
private List<MarcaModelo> listaModelo;

// get e set

// meu metodo no dao
public List<MarcaModelo> RecuperarMarcas() {
		String sql = "SELECT * FROM tb_marca";
		try {
			PreparedStatement ps = conexao.prepareStatement(sql);
			ResultSet rs = ps.executeQuery();
			List<MarcaModelo> listaMarcas = new ArrayList<MarcaModelo>();
			
			while (rs.next()){
				
				MarcaModelo marca = new MarcaModelo();
				marca.setIdMarca(rs.getString("id"));
				marca.setNomeMarca(rs.getString("nome"));
				
				listaMarcas.add(marca);
			}
			
			rs.close();
			System.out.println("Sucesso no metodo Listar Marcas");
			return listaMarcas;
		} catch (Exception e) {
			System.out.println("erro no metodo listar marca");
			e.printStackTrace();
		}
		return null;
	}