Beamer bullets inside parbox

Question

I don´t know why bullets does not appear inside parbox when I use itemize. Can someone help me?

\documentclass{beamer}
 \usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
 \usepackage[spanish]{babel}

\usepackage{tikz}
\usetikzlibrary{arrows,chains,shapes,decorations.markings}
\usepackage{graphicx}
\usepackage{enumitem}



\usetheme{Copenhagen} 
\usecolortheme{lily} 
\useoutertheme{tree}
\useinnertheme{circles} 

\begin{document}

 \begin{frame}
 \begin{figure} [!htbp]
 \centering
 \resizebox{1\textwidth}{!}{
 \begin{tikzpicture}
 [node distance=1.3em,
  %Define style for boxes
  punktchain/.style={ font=\footnotesize, rectangle,  rounded corners,       draw=black,   very thick,  inner sep=.3em,   minimum height=14em,   text  centered,  on chain},
  line/.style={draw, thick, <-},
  every join/.style={->, very thick,shorten >=1pt},
   start chain=going right]

 \node[punktchain, join, text width=.2\textwidth,] [label={[align =center,text width=.2\textwidth] Descripción del Problema Real}](intro) { Ubicación de puntos de recolección y distancias entre ellos};

 \node[punktchain,  join, text depth = 7em,  text width=.25\textwidth] [label={[align =center,text width=.22\textwidth]Representación Matemática}] (probf) {};

 \node[draw, text width=.23\textwidth, text centered, minimum height=5.5em ] at ([yshift=-.5em]probf.center)[label={[align =center,text width=.17\textwidth] {\footnotesize  Casos ATSP y ACVRP}}] {\parbox{\textwidth}{
  \begin{itemize}[leftmargin=*]
  \itemsep0em
  \vspace*{-.8\baselineskip}
  \item {\footnotesize Diseño de Grafo}
   \item {\footnotesize Formulación matemática del problema}\vspace*  {-.8\baselineskip}
\end{itemize}
}};
 \node[punktchain, join, text width=.43\textwidth] (opt)      [label=Optmización de rutas]{};

 \node[font=\footnotesize, draw, text width=.19\textwidth,minimum height=11.2em, text centered ] at ([xshift=-.11\textwidth, yshift=-.05\textheight]opt.center) [label={[align =center,text width=.17\textwidth] {\footnotesize Algoritmos ACO}}] (alg) {};

   \node[font=\footnotesize, draw, text width=.19\textwidth,minimum height=11.2em, text centered ] at ([xshift=.11\textwidth, yshift=-.05\textheight]opt.center) [label={[align =center,text width=.17\textwidth] {\footnotesize Optimización Local}}] (loc) {};

 \node[font=\footnotesize, draw, text width=.17\textwidth, minimum height=4.3em,text centered ] at ([yshift=1.8em]alg.center) [label={\footnotesize Caso ATSP}] (TSP){\parbox{\textwidth}{
\begin{itemize}[leftmargin=*]
\itemsep-.3em
\vspace*{-.5\baselineskip}
\item {\scriptsize AS}
\item  {\scriptsize EAS}
\item  {\scriptsize MMAS}
\item  {\scriptsize ACS}\vspace*{-.6\baselineskip}
\end{itemize}
}};

  \node[font=\footnotesize, draw, text width=.17\textwidth, minimum height=2.6em,text centered ] at ([yshift=-3.5em]alg.center) [label={\footnotesize Caso ACVRP}] (VRP){\parbox{\textwidth}{
\begin{itemize}[leftmargin=*]
 \itemsep-.3em
\vspace*{-.8\baselineskip}
\item {\scriptsize MMAS}
\item {\scriptsize ACS}\vspace*{-\baselineskip}
 \end{itemize}
}};
 \node[font=\footnotesize, draw, text width=.17\textwidth, minimum height=1.5em,text centered ] at ([yshift=.15\textheight]loc.center) [label= {\footnotesize Caso ATSP}] (locTSP){\parbox{\textwidth}{
\begin{itemize}[leftmargin=*]
\itemsep0em
\vspace*{-.3\baselineskip}
\item {\scriptsize \textit{3-opt}}
\vspace*{-.6\baselineskip}
\end{itemize}
}};


\node[font=\footnotesize, draw, text width=.17\textwidth, minimum height=3.2em,text centered ] at ([yshift=-3.7em]loc.center) [label={\footnotesize Caso ACVRP}] (locvrp) {\parbox{\textwidth}{
\begin{itemize}[leftmargin=*]
 \itemsep-1.3em
\vspace*{-.8\baselineskip}
\item {\scriptsize \textit{3-opt}}
\item {\scriptsize Relocalización}
\item {\scriptsize Intercambio}\vspace*{-\baselineskip}
 \end{itemize}
}};

 \node[punktchain, join, text width=.17\textwidth] (result)       [label=Resultados]{Rutas Optimizadas};

\node[draw=none, text width=.02\textwidth, minimum height=1em,text centered ] at ([yshift=-.7em]TSP.north)  (aux1) {};
\node[draw=none, text width=.115\textwidth, minimum height=1em,text centered ] at ([yshift=-.7em]locTSP.north)  (aux2) {};
\node[draw=none, text width=.1\textwidth, minimum height=1em,text centered ] at (VRP.center)  (aux3) {};
\node[draw=none, text width=.115\textwidth, minimum height=1em,text centered ] at ([yshift=.2em]locvrp.center)  (aux4) {};
 \draw [<->, very thick]  (aux1) edge (aux2);
 \draw [<->, very thick]  (aux3) edge (aux4);
\end{tikzpicture}}

\end{figure}

\end{frame}
\end{document}