There are a number of threats which are causing a decline in the population of Tansy beetles along the River Ouse.

The non-native Himalayan balsam (Impatiens glandulifera) is rapidly expanding along river banks and out-competing the resident tansy plants.
Proliferation of riverside trees such as willow, cast dense shade which tansy plants will not tolerate.
Changes in agricultural practices such as an increase in stock numbers lead to the loss of the tansy clumps through overgrazing. Likewise use of herbicides and insecticides can affect tansy clumps.
Eggs and larvae of the Tansy beetle are vulnerable to summer flooding. The adult beetle is less severely affected, as they use the air trapped under their wing cases to float. This may enable beetles to colonise new tansy plant clumps when they are washed downstream.
Research has shown that Tansy beetles do not fly regularly. They have been reported flying once in the Netherlands. Furthermore they will only walk approximately 200 metres. Under these circumstances, losses in tansy plant clumps could lead to greater losses amongst exploring Tansy beetles.

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