Scala: argument type mismatch when invoke list parameters

I want to invoke function with list parameters, this is the code:

class A {
  def cat(s1: String, s2: String) = s1 + " " + s2
}
val a = new A
val mylist = Array("hello","guys")
val argtypes = mylist.map(_.getClass)
val method = a.getClass.getMethod("cat",argtypes: _*)
method.invoke(a,argtypes: _*)

but I get errors:

java.lang.IllegalArgumentException: argument type mismatch at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:606)

How can i do it?