The first note of fear is found in his eighth _Catalepton_:

Villula, quae Sironis eras, et pauper agelle,
Verum illi domino tu quoque divitiae,
Me tibi et hos una mecum, quos semper amavi,
Si quid de patria tristius audiero,
Commendo imprimisque patrem: tu nunc eris illi
Mantua quod fuerat quodque Cremona prius.

It is usually assumed from this passage that Siro had recently died,
probably, therefore, some time in 42 B.C., and that, in accordance with a
custom frequently followed by Greek philosophers at Rome, he had left his
property to his favorite pupil. The garden school, therefore, seems to
have come to an end, though possibly Philodemus may have continued it
for the few remaining years of his life. Siro's villa apparently proved
attractive to Vergil, for he made Naples his permanent home, despite the
gift of a house on the Esquiline from Maecenas.

This, however, is not Vergil's last mention of Siro, if we may believe
Servius, who thinks that "Silenum" in the sixth _Eclogue_ stands for
"Sironem," its metrical equivalent. If, as seems wholly likely, Servius
is right, the sixth _Eclogue_ is a fervid tribute to a teacher who
deserves not to be forgotten in the story of Vergil's education. The poem
has been so strangely misinterpreted in recent years that it is time to
follow out Servius' suggestion and see whether it does not lead to some
conclusions.[5]

[Footnote 5: Skutsch roused a storm of discussion over it by insisting
that it was a catalogue of poems written by Gallus (_Aus Vergils
Frühzeit_.) Cartault, _Étude sur les Bucoliques de Virgile_ (p. 285),