Suppresses thoracic features almost as well as Ubx^Ia.hs (e.g. the disappearance of Keilin's organs in thoracic segments), but is not as effective at inducing abdominal features as Ubx^Ia.hs. Shift in position and axon projection pattern in the posterior compartments of the thoracic segments is not as pronounced as for Ubx^Ia.hs. PNS elements that disappear from A1 with high frequency in Ubx^MX17 appear with low frequency in the thoracic segments of Ubx^IVa.hs, and vice versa. Ubx^Ia.hs and Ubx^IVa.hs are equally effective at promoting changes in cuticular features such as denticle belts.

Heat induction greater than ten minutes results in transformation of parasegments 1 through 5 into five additional copies of parasegment 6 with parasegment 6 like denticle belts. Head involution is completely blocked, formation of head specific structures is suppressed. Formation of both the Keilin's organs and ventral pits is suppresses in all three thoracic parasegments. PNS of thoracic parasegments is not transformed into that of abdominal segments. Very short heat shocks 72 hours after egg laying produce viable adult flies with transformation of antennae into legs, rare transformations of eye into thoracic cuticle causing a rough eye phenotype and few transformations of haltere to wing material.