Ok, so the Expendable rule reads:
Expendable: The Hive Mind thinks no more of expending lesser creatures in battle than most commanders consider expending ammunition.

Expendable units do not generate Blast markers when they are removed as casualties. This includes special effects which create Blast Markers when the unit is targeted. Unless otherwise noted, expendable units DO count as casualties for the purposes of assault resolution (EA1.12.7). All Brood creatures are considered expendable.

(my emphasis)

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Vitai lampada
Sir Hemry Newbolt