The majority of lethality in flies expressing HmgcrNIG.10367 under the control of Scer\GAL4Hmgcr.B is found in newly molted 2nd instar larval and newly moulted 3rd instar larvae. Many larvae dying at the 1st to 2nd instar molt display a classical 'ultraspiracle' phenotype, where apolysed 2nd instar posterior spiracles and mouthparts are juxtaposed near the prior 1st instar posterior spiracles and mouthparts. At each larval-larval molt, some other larvae progressed slightly beyond the unecdysed "ultraspiracle" phenotype, and attained an incomplete ecdysis before dying. Some larvae can only split the apolysed 2nd instar cuticle along the middle of the body, and not remove the remainder of the cuticle from either the mouthparts or the posterior end. In other (the majority of) cases the mouthparts are freed, but the old cuticle remains caught only on the posterior end and is dragged along as the dying larva attempt to move.
Less than 5% of flies expressing HmgcrNIG.10367 under the control of Scer\GAL4Hmgcr.B survive to pupariation. Some of these larvae become developmentally arrested at the pupariation stage with variation in phenotype. Most that are arrested stop development after sclerotization of the puparium but prior to eversion to the white pupa stage. A minor proportion are observed to cease feeding, become sessile, evert their anterior spiracles, but then fail to sclerotize a puparium.
Approximately 14% of flies expressing HmgcrNIG.10367 under the control of Scer\GAL4Hmgcr.B show the normal splaying of papillae on both everted spiracles, as compared to 94.7% of controls.
HmgcrNIG.10367 expressing larvae (under the control of Scer\GAL4Hmgcr.B) display behavioural changes where they show considerable strain and tension in the body (giving the impression that they larvae are trying to ecdyse). These larvae frequently die on the side of the glass vial, sometimes with the cast 2nd instar exoskeleton nearby on the side of the glass vial.
HmgcrNIG.10367 expressing larvae (under the control of Scer\GAL4Hmgcr.B) that have been fed only JH III or only methyl farnesoate, or both together die prior to becoming newly molted third instar larvae. However, treatment with farnesol, a precursor to the synthesis of all three methyl farnesoids normally secreted by the ring glands, exerts a rescue effect. nearly all farnesol-treated larvae are rescued to fully ecdyse and release the second instar cuticle. Additionally, these larvae exhibit the wild-type behaviour of conducting ecdysis under the food surface.
HmgcrNIG.10367 expressing larvae (under the control of Scer\GAL4Hmgcr.B) exhibit a fully penetrant phenotype of melanization of the tracheal system, especially the two main dorsal tracheal trunks. Once the 2nd to 3rd instar larval molt has been reached, the melanization spread anteriorly up each tracheal trunk over the next several hours. During this anterior spread, the pattern in many larvae would pass through a phase in which the melanization first seems localised to periodically distributed foci, often paralleling each other on each tracheal trunk. The melanization would then spread to the intervening areas of the tracheal trunks, making a pair of continuous stripes anteriorly up the body of the larva. The vast majority of these larvae become moribund within several hours of the 2nd to 3rd instar molt. However, a very small percentage attain pupariation and an even smaller proportion reaches pupation.