SPListItemCollection webParts = webPartGallery.GetItems(query);
if (webParts == null || webParts.Count == 0)
{
throw new ArgumentOutOfRangeException("webPartName", "Webpart not found in gallery");
}

SPListItem item = webParts[0];

string error;
XmlTextReader reader = new XmlTextReader(item.File.OpenBinaryStream());
WebPart webPart = manager.ImportWebPart(reader, out error);

if (string.IsNullOrEmpty(error))
{
manager.AddWebPart(webPart, "ZoneId", zoneIndex);
}