I thank you all for your answers, and they have certainly been helpful, but it seems my question is being interpreted more narrowly than I meant it, and looking back at what I posted it seems clear why, and my apologies.
While everything so far posted does answer my question, I was using the title theotokos out of habit as a term of address, I'm actually wondering about significant writings about St. Mary herself by the Church Fathers.
To get more to the point, I'm wondering how early we have definitive evidence of her veneration. This is not, for the record, an area I am struggling with, however I do know some who do and I lack the knowledge to present a definitive evidence of pre-Ephesus veneration of Mary, other than the fact that the veneration seems taken for granted at that council and therefore certainly predates it.
edit: I find it remarkable that "Beneath your protection" is that early though. I had assumed it was a much later composition.
St. Irenaeus c. 180 Against Heresies (Book III, Chapter 22)
1. Those, therefore, who allege that He took nothing from the Virgin do greatly err, [since,] in order that they may cast away the inheritance of the flesh, they also reject the analogy [between Him and Adam]. For if the one [who sprang] from the earth had indeed formation and substance from both the hand and workmanship of God, but the other not from the hand and workmanship of God, then He who was made after the image and likeness of the former did not, in that case, preserve the analogy of man, and He must seem an inconsistent piece of work, not having wherewith He may show His wisdom. But this is to say, that He also appeared putatively as man when He was not man, and that He was made man while taking nothing from man. For if He did not receive the substance of flesh from a human being, He neither was made man nor the Son of man; and if He was not made what we were, He did no great thing in what He suffered and endured. But every one will allow that we are [composed of] a body taken from the earth, and a soul receiving spirit from God. This, therefore, the Word of God was made, recapitulating in Himself His own handiwork; and on this account does He confess Himself the Son of man, and blesses the meek, because they shall inherit the earth. Matthew 5:5 The Apostle Paul, moreover, in the Epistle to the Galatians, declares plainly, God sent His Son, made of a woman. Galatians 4:4 And again, in that to the Romans, he says, Concerning His Son, who was made of the seed of David according to the flesh, who was predestinated as the Son of God with power, according to the spirit of holiness, by the resurrection from the dead, Jesus Christ our Lord. Romans 1:3-4 http://www.newadvent.org/fathers/0103322.htm
2. Superfluous, too, in that case is His descent into Mary; for why did He come down into her if He were to take nothing of her? Still further, if He had taken nothing of Mary, He would never have availed Himself of those kinds of food which are derived from the earth, by which that body which has been taken from the earth is nourished; nor would He have hungered, fasting those forty days, like Moses and Elias, unless His body was craving after its own proper nourishment; nor, again, would John His disciple have said, when writing of Him, But Jesus, being wearied with the journey, was sitting [to rest]; John 4:6 nor would David have proclaimed of Him beforehand, They have added to the grief of my wounds; nor would He have wept over Lazarus, nor have sweated great drops of blood; nor have declared, My soul is exceeding sorrowful; Matthew 26:38 nor, when His side was pierced, would there have come forth blood and water. For all these are tokens of the flesh which had been derived from the earth, which He had recapitulated in Himself, bearing salvation to His own handiwork.
3. Wherefore Luke points out that the pedigree which traces the generation of our Lord back to Adam contains seventy-two generations, connecting the end with the beginning, and implying that it is He who has summed up in Himself all nations dispersed from Adam downwards, and all languages and generations of men, together with Adam himself. Hence also was Adam himself termed by Paul the figure of Him that was to come, Romans 5:14 because the Word, the Maker of all things, had formed beforehand for Himself the future dispensation of the human race, connected with the Son of God; God having predestined that the first man should be of an animal nature, with this view, that he might be saved by the spiritual One. For inasmuch as He had a pre-existence as a saving Being, it was necessary that what might be saved should also be called into existence, in order that the Being who saves should not exist in vain.
4. In accordance with this design, Mary the Virgin is found obedient, saying, Behold the handmaid of the Lord; be it unto me according to your word. Luke 1:38 But Eve was disobedient; for she did not obey when as yet she was a virgin. And even as she, having indeed a husband, Adam, but being nevertheless as yet a virgin (for in Paradise they were both naked, and were not ashamed, Genesis 2:25 inasmuch as they, having been created a short time previously, had no understanding of the procreation of children: for it was necessary that they should first come to adult age, and then multiply from that time onward), having become disobedient, was made the cause of death, both to herself and to the entire human race; so also did Mary, having a man betrothed [to her], and being nevertheless a virgin, by yielding obedience, become the cause of salvation, both to herself and the whole human race. And on this account does the law term a woman betrothed to a man, the wife of him who had betrothed her, although she was as yet a virgin; thus indicating the back-reference from Mary to Eve, because what is joined together could not otherwise be put asunder than by inversion of the process by which these bonds of union had arisen; so that the former ties be cancelled by the latter, that the latter may set the former again at liberty. And it has, in fact, happened that the first compact looses from the second tie, but that the second tie takes the position of the first which has been cancelled. For this reason did the Lord declare that the first should in truth be last, and the last first. Matthew 19:30, Matthew 20:16 And the prophet, too, indicates the same, saying, instead of fathers, children have been born unto you. For the Lord, having been born the First-begotten of the dead, Revelation 1:5 and receiving into His bosom the ancient fathers, has regenerated them into the life of God, He having been made Himself the beginning of those that live, as Adam became the beginning of those who die. 1 Corinthians 15:20-22 Wherefore also Luke, commencing the genealogy with the Lord, carried it back to Adam, indicating that it was He who regenerated them into the Gospel of life, and not they Him. And thus also it was that the knot of Eve's disobedience was loosed by the obedience of Mary. For what the virgin Eve had bound fast through unbelief, this did the virgin Mary set free through faith.