Clean up module usage. There's no need to use InstanceMethods -- normal Ruby modules and includes will work fine here.

lib/activerecord-import/active_record/adapters/mysql2_adapter.rb

@@ -2,5 +2,5 @@ require "active_record/connection_adapters/mysql2_adapter"
 require "activerecord-import/adapters/mysql_adapter"
 
 class ActiveRecord::ConnectionAdapters::Mysql2Adapter
-  include ActiveRecord::Import::MysqlAdapter::InstanceMethods
+  include ActiveRecord::Import::MysqlAdapter
 end

lib/activerecord-import/active_record/adapters/mysql_adapter.rb

@@ -2,5 +2,5 @@ require "active_record/connection_adapters/mysql_adapter"
 require "activerecord-import/adapters/mysql_adapter"
 
 class ActiveRecord::ConnectionAdapters::MysqlAdapter
-  include ActiveRecord::Import::MysqlAdapter::InstanceMethods
+  include ActiveRecord::Import::MysqlAdapter
 end

lib/activerecord-import/active_record/adapters/postgresql_adapter.rb

@@ -2,6 +2,6 @@ require "active_record/connection_adapters/postgresql_adapter"
 require "activerecord-import/adapters/postgresql_adapter"
 
 class ActiveRecord::ConnectionAdapters::PostgreSQLAdapter
-  include ActiveRecord::Import::PostgreSQLAdapter::InstanceMethods
+  include ActiveRecord::Import::PostgreSQLAdapter
 end
 

lib/activerecord-import/active_record/adapters/sqlite3_adapter.rb

@@ -2,6 +2,6 @@ require "active_record/connection_adapters/sqlite3_adapter"
 require "activerecord-import/adapters/sqlite3_adapter"
 
 class ActiveRecord::ConnectionAdapters::Sqlite3Adapter
-  include ActiveRecord::Import::Sqlite3Adapter::InstanceMethods
+  include ActiveRecord::Import::Sqlite3Adapter
 end
 

lib/activerecord-import/adapters/mysql_adapter.rb

@@ -1,11 +1,6 @@
 module ActiveRecord::Import::MysqlAdapter
-  module InstanceMethods
-    def self.included(klass)
-      klass.instance_eval do
   include ActiveRecord::Import::ImportSupport  
   include ActiveRecord::Import::OnDuplicateKeyUpdateSupport
-      end
-    end
 
   # Returns the maximum number of bytes that the server will allow
   # in a single packet
@@ -56,4 +51,3 @@ module ActiveRecord::Import::MysqlAdapter
     exception.is_a?(ActiveRecord::StatementInvalid) && exception.to_s.include?('Duplicate entry')
   end
 end
-end

lib/activerecord-import/adapters/postgresql_adapter.rb

@@ -1,13 +1,7 @@
 module ActiveRecord::Import::PostgreSQLAdapter
-  module InstanceMethods
-    def self.included(klass)
-      klass.instance_eval do
   include ActiveRecord::Import::ImportSupport
-      end
-    end
 
   def next_value_for_sequence(sequence_name)
     %{nextval('#{sequence_name}')}
   end
 end
-end

lib/activerecord-import/adapters/sqlite3_adapter.rb

@@ -1,7 +1,5 @@
 module ActiveRecord::Import::Sqlite3Adapter
-  module InstanceMethods
   def next_value_for_sequence(sequence_name)
     %{nextval('#{sequence_name}')}
   end
 end
-end