You can use https, is this for token-secured service? QueryTask, like the other tasks have a Token property if you want to set this explicitly. Or you can also enable IdentityManager with SignInDialog or your own control that lets you set username/password for the secured service.
To use IdentityManager and SignInDialog, you can refer to the Security samples here: ArcGIS API for Silverlight - Interactive Samples | ArcGIS for Developers (should be similar to WPF).
Or if you have a token string, set QueryTask.Token property. If you have to go through a proxy, there's also ProxyUrl.
This doc might help : ArcGIS Runtime SDK for WPF
thank you for the speey reply
the odd thing is that a URL (http://services.arcgis.com/pmcEyn9tLWCoX7Dm/ArcGIS/rest/services/TimeZoneFeatures/FeatureServer/0) has either been changed or the security protocol has changed so I need to update the http with https yet when I change the URL in code and step through the code the URL does not reflect the new https but retains the http....frustrating.