Does a court have a sua sponte duty to instruct a defendant on a defense of mistaken belief?

A court has a sua sponte duty to instruct on a defense only if the defendant appeared to rely on the defense, or if substantial evidence supports the defense and it is not inconsistent with the defendant's theory of the case. (People v. Barton (1995) 12 Cal.4th 186, 195.) Here, defendant did not rely on a mistaken belief defense. Instead, defense counsel's closing argument attempted to persuade the jury that the evidence was insufficient to prove beyond a reasonable doubt that defendant was motivated by an unnatural or abnormal sexual interest in the child.