After the Italian lineout fell apart Del Fava misses out altogether as Manoa Vosowai comes on to the bench for his first appearance in the tournament.
Italy conceded eight tries at Twickenham as they were hammered 59-13 and Mallett was unwilling to risk Orquera against the big running Jamie Roberts on Saturday.
"Three of the tries we conceded came directly from missed tackles by Orquera," said the South African Mallett.
"We had to look at the fly-half role because Wales are going to send people like Roberts down the ten channel.
"Wales are going to try to play a fast game to try to replicate the game England played so it's really important we get our defence right.
"The lineout issues come from a variety of reasons. We tried to put Sergio Parisse in the backline instead of calling the lineout but it didn't work because we couldn't secure our own ball.
"Things did change a little when Santiago Dellape and Fabio Ongaro came on for the last half hour because Santiago started making the lineout calls.
"Unfortunately Fabio is injured but Carlo Festuccia has been playing well for Racing Metro and has a lot of experience so I have no worries about him being on the bench.
"And it's a big advantage having a genuine loose forward in Vosowai on the bench rather than a lock out of position."
15 - Luke McLean (Treviso)
14 - Andrea Masi (Racing Metro)
13 - Gonzalo Canale (Clermont Auvergne)
12 - Alberto Sgarbi (Treviso)
11 - Mirco Bergamasco (Racing Metro)
10 - Kris Burton (Treviso)
9 - Fabio Semenzato (Treviso)
1 - Salvatore Perugini (Aironi)
2 - Leonardo Ghiraldini (Treviso)
3 - Martin Castrogiovanni (Leicester Tigers)
4 - Santiago Dellape (Racing Metro)
5 - Quintin Geldenhuys (Aironi)
6 - Robert Barbieri (Treviso)
7 - Alessandro Zanni (Treviso)
8 - Sergio Parisse (Stade Francais) (captain)
16 - Carlo Festuccia (Racing Metro)
17 - Andrea Lo Cicero (Racing Metro)
18 - Valerio Bernabo (Treviso)
19 - Manoa Vosowai (Treviso)
20 - Pablo Canavosio (Aironi)
21 - Luciano Orquera (Brive)
22 - Tommaso Benvenuti (Treviso)