Recently we discovered that our sitemaps-- the list of pages on the site-- for Yahoo and Bing were not updating on their own. Google handles this task automatically, so we had blissfully assumed it was the same case with everyone else. Unfortunately, it does not seem to be. You should manually ping the other major search engines each time your sitemap changes.
To help save you the time, here are all the addresses you need to hit:
Google Sitemap Ping Address:
http://www.google.com/webmasters/tools/ping?sitemap=[your sitemap url]
Yahoo! Sitemap Ping Address
http://search.yahooapis.com/SiteExplorerService/V1/ping?sitemap=[your sitemap url]
Ask.com Sitemap Ping Address
http://submissions.ask.com/ping?sitemap=[your sitemap url]
Microsoft Bing Sitemap Ping Address
http://www.bing.com/webmaster/ping.aspx?siteMap=[your sitemap url]
You can also include your sitemap (or sitemap of sitemaps) in your robots.txt file.
Just add the following directive to robots.txt:
Hope this helps! Happy sitemap indexing! For more information, check out the sitemap protocol site.