\tikzstyle{every edge}=[-,>=stealth',shorten >=1pt,auto,thin,draw]
% Upper level
\tikzstyle{every state}=[draw=none,text=white,scale=0.55, font=\scriptsize, transform shape]
% premier cluster
\tikzstyle{every node}=[fill=green!50!blue!20!white]
\node[state] (N1) at (0.05,3) {\includegraphics[width=.2\textwidth]{pollen.png}};
\node[state, right = of N1] (N2)  {\includegraphics[width=.2\textwidth]{pollen.png}}; % at (.75,3)
\node[state, right = of N2] (N3) {\includegraphics[width=.2\textwidth]{pollen.png}}; % at (1.5,3) 
%           \node[state] (N5) at (3,3) {\includegraphics[width=.1\textwidth]{pollen.png}};
%           \node[state] (N6) at (3.75,3) {\includegraphics[width=.1\textwidth]{pollen.png}};

\tikzstyle{every node}=[shape=rectangle,fill=red!50!blue!20!white]
%         \node[state, fill = white] (P) at (-1.5, 0) {\includegraphics[width=.08\textwidth]{bee.png}};
\node[state, tokens=0] (P1) at (-1, 0) {\includegraphics[width=.2\textwidth]{bee.png}};
\node[state, tokens=0, right = of P1] (P2) {\includegraphics[width=.2\textwidth]{bee.png}}; %  at (-.25, 0)
\node[state, tokens=0, right = of P2] (P3) {\includegraphics[width=.2\textwidth]{bee.png}}; %at (.5, 0) 
\node[state, tokens=0, right = of P3] (P4) {\includegraphics[width=.2\textwidth]{bee.png}}; % at (1.25, 0) 

\tikzstyle{every edge}=[>=stealth,shorten >=1pt,auto,thin,draw]
\path (P1) edge  (N1);
\path (P2) edge  (N1);
\path (P3) edge  (N1);
\path (P4) edge  (N2);
\path (P4) edge  (N1);
\path (P1) edge  (N3);
