How i call method from plugin in response to event in a host application in c#?

I have created a simple application with plugin system using reflection, it is working very well. I want to handle the event in the host application using the method, which is provided in the plugin. how can i do this. my application code are as follow

Plugin Manager

namespace PluginManager
{
    public interface PluginImplementor
    {
        string PluginName();
        void MenuAdder(ToolStripItem m);
    }
}  

Host Application

namespace MYPLUGINAPP
{
    public partial class Form1 : Form
    {
        PluginImplementor PM;
        ToolStripItem ts;
        string[] DllAdd = new string[1000];
        PluginsInfo pi = new PluginsInfo();
        bool formplugin = false;
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            LoadPlugins();
        }

        private void addPluginToolStripMenuItem_Click(object sender, EventArgs e)
        {
            if (openFileDialog1.ShowDialog() == DialogResult.OK && openFileDialog1.FileName.Length > 0)
            {
                string filename = openFileDialog1.SafeFileName;
                string targetAdd = @"../../Plugins";
                string target = System.IO.Path.Combine(targetAdd, filename);
                System.IO.File.Copy(openFileDialog1.FileName, target, true);
                LoadPlugins();
                pi.listBox1.Items.Add(PM.PluginName());
            }
        }

        public void LoadPlugins()
        {
            foreach (var files in Directory.GetFiles(@"../../Plugins", "*dll"))
            {
                var assembly = Assembly.LoadFrom(@"../../Plugins" + files);
                foreach (var type in assembly.GetTypes())
                {
                    if (type.GetInterfaces().Contains(typeof(PluginImplementor)))
                    {
                        PM = Activator.CreateInstance(type) as PluginImplementor;
                        string name = PM.PluginName();
                        ts = menuStrip1.Items.Add(name);
                        PM.MenuAdder(ts);
                    }
                }
            }
        }

        private void showInstalledPluginsToolStripMenuItem_Click(object sender, EventArgs e)
        {
            pi.ShowDialog();
        }
    }
}  

Plugin

namespace Library_Plugin
{
    public class Starter : PluginImplementor
    {
        public string PluginName()
        {
            return "Hello";
        }

        public void MenuAdder(System.Windows.Forms.ToolStripItem ts)
        {
            ts.Click += ts_Click;
        }

        void ts_Click(object sender, EventArgs e)
        {
            System.Windows.Forms.MessageBox.Show("I am plugin");
        }

    }
}

Please provide any better way through i can solve this problem, if i am doing it wrong.

Thanks in Advance