Three into nine won't go.

Or, to put it another way, when you have a trio of international scrum-halves on your books then you are bound to have a problem keeping them all content. Finding a way to accommodate Chris Cusiter, Niko Matawalu and Henry Pyrgos is the sort of headache that many coaches would be happy to suffer, but Gregor Townsend acknowledges that it can be difficult at times.

Cusiter, who missed almost all of last season with a shoulder injury, has been given the starting berth for Glasgow Warriors' RaboDirect PRO12 match with Munster at Scotstoun tonight, with Matawalu offering cover from the bench. That formula reverses the selection for last Sunday's Heineken Cup meeting with Exeter Chiefs - Cusiter was not actually used on that occasion - and head coach Townsend explained that managing so much talent is one of the challenges of his job.

"We have great competition in a number of positions, one of them being scrum-half," said Townsend. "In the last three games we've had three different nines, and it's great for me as a coach that we have that quality. It's part of coaching. They all want to play, as I would if I was a player. They all understand that competition is here and they are up against very good players. My aim - and hopefully theirs - is to make sure that brings out the best from them. It should be positive that players know they need to play well. They all have different strengths, but they are all good players with very good basic skills. It has to be a positive for the team."

Townsend refused to rise to the bait of a question that suggested he might be taking a leaf out of Sir Alex Ferguson's book by indulging in mindgames with his players, but he conceded that elements of motivational psychology come into the coaching mix.

"The goal is to get them physically right, but also mentally right," he explained. "Whether keeping them on their toes is the phrase [is questionable]. It's just about making sure they know they have to play well to keep their places in the team. We have a lot of competition, but we back them whether they are in the team or not. Sometimes it works and sometimes it doesn't."

Townsend must certainly hope that leaving Cusiter out of his squad to play Toulon a fortnight ago, followed by his decision not to bring him off the bench last weekend, is one of those things that does work when the 31-year-old, who also takes over as captain from the rested Al Kellock, is one of those things that ends up working rather well.

"Experience, competitiveness, skill,' was how the coach summed up the player who was, briefly, his half-back partner when both played for the Border Reivers almost a decade ago, but Cusiter's wounded pride may be just as important a factor against the side lying second behind the unbeaten Warriors in the table.

For his part, Cusiter did not deny that the selection roller coaster can be an uncomfortable ride at times. "Gregor is the boss, the head coach and he has the right to make these calls.," said the veteran of 62 Scotland appearances. "I can only control how I play and that is what I plan to do.

"I feel I have played really well this year. That is why it was frustrating to miss these games. Most guys are the same. If you are at this level you are ultra competitive and you have to be a bit selfish. I want to play.

"I respect the other guys and their ability but we are all different. I would always back myself to do a good job. It is not in our hands. It is in Gregor's hands. We stake our case whenever we get an opportunity. If you don't play well it could be another three weeks or longer before you play again."

In truth, there are few other surprises in Townsend's line-up. If keeping players honest is one principle worth following, then rewarding top-notch performances is another. Hence, the selection en masse of an unchanged back row of Rob Harley, Tyrone Holmes and Josh Strauss, whose efforts, collective and individual, against Exeter were outstanding.

Elsewhere, there is a considerable boost for the side in the return, at inside centre, of Sean Lamont, who had also seemed rejuvenated through the early weeks of the season until he suffered a calf injury. Duncan Weir takes over from Ruaridh Jackson at fly-half, reforming the partnership that looked so effective against Scarlets in the Warriors' last PRO12 outing, three weeks ago.

At the other end of the M8, Edinburgh will seek to build on the promise they have shown in their two Heineken Cup matches - a win against Munster and a loss to Perpignan - as they take on Treviso at Murrayfield. The Italian side were tipped by many to make a real challenge this season, but two wins from five games has not exactly marked them out as PRO12 title contenders. Still, it is one more victory than Edinburgh, still bottom of the table, have managed to date.

The capital side's preparations to face Perpignan last weekend were disrupted when Scotland internationals Matt Scott and Dave Denton withdrew on the morning of the match. However, the pair are back in harness, at inside centre and No.8 respectively, and coach Alan Solomons believes his side is starting to find its feet. "I said right at the beginning that our pre-season would take place over this initial period of nine competitive games. That's now drawing to a close, so I'm pleased with the progress. If we deliver a good performance we will get the result, but we have to deliver a really good performance against very good opposition to get that."