Calling orchestras ``Western'' is really a misnomer since it is the norm these days, but I am sticking with the name as a type of contrast to that of the traditional Chinese orchestra. The key property of a ``western'' orchestra is the homogeneity of sound within each section, and how each section manages to blend with the others while performing parts of a symphony. This, coupled with modern music theory, is one of the reasons why many places (countries or otherwise) will almost always have a ``western'' orchestra, in addition to any other ethnic orchestra that they might have.
The purpose of a dizi within the context of the ``western'' orchestra is largely confined to that of two possibilities: a solo instrument that uses the philharmonic orchestra as a means of providing accompaniment, or as a ``tone-colour'' instrument to convey a certain oriental aesthetic to a piece.
dizi as Solo in ``Western'' Orchestras
The conduct of the dizi in this circumstance is very similar to that of playing in a traditional Chinese orchestra, but this time with greater emphasis on intonation than ever before. Classically trained musicians of the western tradition are drilled very deeply on intonation, and as a result, tend to be more sensitive to intonation issues than non-classically trained musicians. While the dizi being a solo instrument implies that it has primal dominance over all the other instruments, it is still important to be playing in tune to ensure that the orchestra can uphold their role of proper harmony and/or counterpoint.
In this series of documents, we have pointed out that the tuning for the dizi is standardised at A4=442Hz. This may not be true for the ``western'' orchestras---their tuning may range from A4=435Hz to A4=450Hz, with A4=440Hz being the international standard.
It is often in the player's interest to verify tuning standards of various ``western'' orchestras that they are performing with to ensure that intonation is well within control. It is also under such circumstances that the existence of the tuning slide/tenon, be it single or doubly-inserted tenons proves to be a lifesaver.
Despite the existence of a tuning slide/tenon, be aware that the slide/tenon can only flatten the fundamental frequency of the dizi, and that the maximum amount of lengthening without throwing the array of tone holes completely out of alignment is roughly short of the length of the largest tone hole. When the lengthening is substantial (more than 4mm for example), there may be a need to use the embouchure to ``lip'' the individual notes to the right pitch.
Some players resort to adjusting individual tone holes on the dizi by either scraping or patching, but those are too radical for my taste. If the tuning is sufficiently different that requires such drastic measures, the player is better served with a custom made dizi that is tuned to that particular tuning standard.
dizi as a Tone-Colour Instrument
As noted earlier, the second possible role for the dizi to play in a ``western'' orchestra is that of ``tone-colour'' or 色彩乐器 (secai yueqi). As a ``tone-colour'' instrument, intonation is of course still important, but what is more important than that is the ability to apply techniques that can bring out that folk aesthetic that some composers are looking for.
Since the dizi is not a standard instrument for the ``western'' orchestra, there is a tendency to avoid using it for the equally important role of harmony development. The dizi is ideal for cases where the sound from the woodwind sections needs to be brightened significantly.
Since the dizi in this circumstance is supposed to be for a specialised role, it is often unsurprising to find long periods of rest within the piece.