diff --git a/django/db/backends/mysql/base.py b/django/db/backends/mysql/base.py
index 7a59ecd612..d7bb129744 100644
--- a/django/db/backends/mysql/base.py
+++ b/django/db/backends/mysql/base.py
@@ -6,18 +6,14 @@ MySQLdb is supported for Python 2 only: http://sourceforge.net/projects/mysql-py
 """
 from __future__ import unicode_literals
 
-import datetime
 import re
 import sys
-import warnings
 
-from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured
 from django.db import utils
 from django.db.backends import utils as backend_utils
 from django.db.backends.base.base import BaseDatabaseWrapper
-from django.utils import six, timezone
-from django.utils.deprecation import RemovedInDjango20Warning
+from django.utils import six
 from django.utils.encoding import force_str
 from django.utils.functional import cached_property
 from django.utils.safestring import SafeBytes, SafeText
@@ -31,7 +27,7 @@ except ImportError as e:
     )
 
 from MySQLdb.constants import CLIENT, FIELD_TYPE                # isort:skip
-from MySQLdb.converters import Thing2Literal, conversions       # isort:skip
+from MySQLdb.converters import conversions                      # isort:skip
 
 # Some of these import MySQLdb, so import them after checking if it's installed.
 from .client import DatabaseClient                          # isort:skip
@@ -51,20 +47,6 @@ if (version < (1, 2, 1) or (
     raise ImproperlyConfigured("MySQLdb-1.2.1p2 or newer is required; you have %s" % Database.__version__)
 
 
-def adapt_datetime_warn_on_aware_datetime(value, conv):
-    # Remove this function and rely on the default adapter in Django 2.0.
-    if settings.USE_TZ and timezone.is_aware(value):
-        warnings.warn(
-            "The MySQL database adapter received an aware datetime (%s), "
-            "probably from cursor.execute(). Update your code to pass a "
-            "naive datetime in the database connection's time zone (UTC by "
-            "default).", RemovedInDjango20Warning)
-        # This doesn't account for the database connection's timezone,
-        # which isn't known. (That's why this adapter is deprecated.)
-        value = value.astimezone(timezone.utc).replace(tzinfo=None)
-    return Thing2Literal(value.strftime("%Y-%m-%d %H:%M:%S.%f"), conv)
-
-
 # MySQLdb-1.2.1 returns TIME columns as timedelta -- they are more like
 # timedelta in terms of actual behavior as they are signed and include days --
 # and Django expects time, so we still need to override that. We also need to
@@ -75,7 +57,6 @@ django_conversions.update({
     FIELD_TYPE.TIME: backend_utils.typecast_time,
     FIELD_TYPE.DECIMAL: backend_utils.typecast_decimal,
     FIELD_TYPE.NEWDECIMAL: backend_utils.typecast_decimal,
-    datetime.datetime: adapt_datetime_warn_on_aware_datetime,
 })
 
 # This should match the numerical portion of the version numbers (we can treat
diff --git a/django/db/backends/oracle/base.py b/django/db/backends/oracle/base.py
index 8e23b95fed..c40a515f33 100644
--- a/django/db/backends/oracle/base.py
+++ b/django/db/backends/oracle/base.py
@@ -10,14 +10,12 @@ import decimal
 import os
 import platform
 import sys
-import warnings
 
 from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured
 from django.db import utils
 from django.db.backends.base.base import BaseDatabaseWrapper
-from django.utils import six, timezone
-from django.utils.deprecation import RemovedInDjango20Warning
+from django.utils import six
 from django.utils.encoding import force_bytes, force_text
 from django.utils.functional import cached_property
 
@@ -326,13 +324,6 @@ class OracleParam(object):
         # without being converted by DateTimeField.get_db_prep_value.
         if settings.USE_TZ and (isinstance(param, datetime.datetime) and
                                 not isinstance(param, Oracle_datetime)):
-            if timezone.is_aware(param):
-                warnings.warn(
-                    "The Oracle database adapter received an aware datetime (%s), "
-                    "probably from cursor.execute(). Update your code to pass a "
-                    "naive datetime in the database connection's time zone (UTC by "
-                    "default).", RemovedInDjango20Warning)
-                param = param.astimezone(timezone.utc).replace(tzinfo=None)
             param = Oracle_datetime.from_datetime(param)
 
         string_size = 0
diff --git a/django/db/backends/sqlite3/base.py b/django/db/backends/sqlite3/base.py
index 89ee9682f2..0c26882a57 100644
--- a/django/db/backends/sqlite3/base.py
+++ b/django/db/backends/sqlite3/base.py
@@ -6,14 +6,12 @@ standard library.
 """
 from __future__ import unicode_literals
 
-import datetime
 import decimal
 import re
 import warnings
 
 import pytz
 
-from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured
 from django.db import utils
 from django.db.backends import utils as backend_utils
@@ -22,7 +20,6 @@ from django.utils import six, timezone
 from django.utils.dateparse import (
     parse_date, parse_datetime, parse_duration, parse_time,
 )
-from django.utils.deprecation import RemovedInDjango20Warning
 from django.utils.encoding import force_text
 from django.utils.safestring import SafeBytes
 
@@ -43,20 +40,6 @@ from .operations import DatabaseOperations                  # isort:skip
 from .schema import DatabaseSchemaEditor                    # isort:skip
 
 
-def adapt_datetime_warn_on_aware_datetime(value):
-    # Remove this function and rely on the default adapter in Django 2.0.
-    if settings.USE_TZ and timezone.is_aware(value):
-        warnings.warn(
-            "The SQLite database adapter received an aware datetime (%s), "
-            "probably from cursor.execute(). Update your code to pass a "
-            "naive datetime in the database connection's time zone (UTC by "
-            "default).", RemovedInDjango20Warning)
-        # This doesn't account for the database connection's timezone,
-        # which isn't known. (That's why this adapter is deprecated.)
-        value = value.astimezone(timezone.utc).replace(tzinfo=None)
-    return value.isoformat(str(" "))
-
-
 def decoder(conv_func):
     """ The Python sqlite3 interface returns always byte strings.
         This function converts the received value to a regular string before
@@ -73,7 +56,6 @@ Database.register_converter(str("timestamp"), decoder(parse_datetime))
 Database.register_converter(str("TIMESTAMP"), decoder(parse_datetime))
 Database.register_converter(str("decimal"), decoder(backend_utils.typecast_decimal))
 
-Database.register_adapter(datetime.datetime, adapt_datetime_warn_on_aware_datetime)
 Database.register_adapter(decimal.Decimal, backend_utils.rev_typecast_decimal)
 if six.PY2:
     Database.register_adapter(str, lambda s: s.decode('utf-8'))
diff --git a/docs/releases/2.0.txt b/docs/releases/2.0.txt
index 9c1d80f081..0982218b92 100644
--- a/docs/releases/2.0.txt
+++ b/docs/releases/2.0.txt
@@ -254,3 +254,8 @@ these features.
   required.
 
 * ``django.db.models.fields.add_lazy_relation()`` is removed.
+
+* When time zone support is enabled, database backends that don't support time
+  zones no longer convert aware datetimes to naive values in UTC anymore when
+  such values are passed as parameters to SQL queries executed outside of the
+  ORM, e.g. with ``cursor.execute()``.