I think this could be Alcaeorrhynchus grandis.
FIRST INSTAR = these are difficult to distinguish from the first instar nymphs of Euthyrhynchus floridanus (Linnaeus): both have a blue-black head and thorax and red abdomen. FAIL on red abdomen
SECOND INSTAR = has become more uniformly brownish with faint markings on the abdomen. FAIL on the brownish part with faint markings on abdomen.
THIRD INSTAR = has acquired red lateral keels on the pronotum and is generally bluish black with a brown abdomen. FAIL on the brownish abdomen.
FOURTH INSTAR = lager keels on pronotum, wing pads visible but not prominent, general color is bluish black. PASS on the general color.
FIFTH AND FINAL INSTAR = has distinct wing pads and very large red keels. FAIL on the distinct wing pads.

This has led me to the conclusion it is in its 4th instar.