Expression of lark^{dsRNA.Scer\UAS.cSb} driven by Scer\GAL4^P2.4.Pdf in a lark¹/+ background results in a significant shortening of circadian period.

lark¹ heterozygotes eclose early compared to control flies.

No defects in locomotor rhythm are observed when flies expressing lark^{dsRNA.Scer\UAS.cSb} under the control of Scer\GAL4^elav-C155 are raised at 25[o]C. However, when the flies are reared at 29[o]C, 21% of flies are arrhythmic and 16% are weakly arrhythmic. Heterozygous lark¹/+ enhances the phenotype further.

No defects in locomotor rhythmicity are observed when flies expressing lark^{dsRNA.Scer\UAS.cSb} under the control of Scer\GAL4^nrv2.PS are raised at 25[o]C. When the flies are reared at 29[o]C, 20% of flies are arrhythmic and 35% are weakly arrhythmic. Heterozygous lark¹/+ enhances the phenotype further; 42% of these flies are arrhythmic.

Only 21% of flies expressing two copies of lark^{dsRNA.Scer\UAS.cSb} under the control of Scer\GAL4^tim.Scer\UAS exhibit robust locomotor rhythms at 29[o]C. This rises to 57% when only one copy of the transgene is expressed. Heterozygous lark¹/+ enhances the phenotype further; 51% of these flies are completely arrhythmic and a further 29% are weakly arrhythmic.

Only 12% of flies expressing two copies of lark^{dsRNA.Scer\UAS.cSb} under the control of Scer\GAL4^P2.4.Pdf (with Dcr-2^Scer\UAS.cDa) in a heterozygous lark¹ background display robust locomotor rhythms. 37% of flies are arrhythmic.

48% of flies expressing lark^{dsRNA.Scer\UAS.cSb} under the control of Scer\GAL4^dimm-929 at 29[o]C exhibit robust locomotor rhythms. The proportion of arrhythmic flies increases when knockdown occurs in a lark¹/+ mutant background.

40% of flies expressing lark^{dsRNA.Scer\UAS.cSb} under the control of Scer\GAL4^Mai179 at 29[o]C exhibit robust locomotor rhythms. The proportion of arrhythmic flies increases when knockdown occurs in a lark¹/+ mutant background.

Only 52% of flies expressing lark^{dsRNA.Scer\UAS.cSb} under the control of Scer\GAL4^dimm-929 (restricted to non-pdf expressing cell types using Scer\GAL80^Pdf.PS) in a lark¹/+ mutant background at 29[o]C exhibit strong locomotor rhythm defects.

Strong locomotor defects are seen in 56% of flies expressing lark^{dsRNA.Scer\UAS.cSb} under the control of Scer\GAL4^Mai179 (restricted to non-pdf expressing cell types using Scer\GAL80^Pdf.PS) in a lark¹/+ mutant background and raised at 29[o]C.

lark¹ animals rescued by lark^{ZF.T:Ivir\HA1} have scutellar bristle defects (such as a missing or malformed posterior scutellar bristle and ectopic bristles). The penetrance of the bristle phenotype is 66-99%. The flies also have a "held out" wing phenotype with 100% penetrance. lark¹ animals rescued by lark^{RRM2.RNP2.T:Ivir\HA1} have scutellar bristle defects (50-100% penetrance) and a "held out" wing phenotype (48-100% penetrance). lark¹ animals rescued by lark^{cMa.T:Ivir\HA1} or lark^{RRM1.RNP2.T:Ivir\HA1} have normal flight behaviour. lark¹ animals rescued by lark^{RRM2+RTZF.T:Ivir\HA1} have scutellar bristle defects (97% penetrance) and an abnormal wing phenotype (94% penetrance). lark¹ homozygotes carrying lark^{cMa.T:Ivir\HA1}, lark^{RRM1.RNP2.T:Ivir\HA1}, lark^{RRM2.RNP2.T:Ivir\HA1} or lark^{ZF.T:Ivir\HA1} show normal eclosion rhythms in 12 hour light:12 hour darkness conditions and normal free-running eclosion rhythms. lark¹ homozygotes carrying lark^{RRM1+RTZF.T:Ivir\HA1} or lark^{RRM2+RTZF.T:Ivir\HA1} have normal free-running eclosion rhythms.

Eggs laid by mothers with homozygous lark¹ germline clones have normal morphology, but are extremely fragile, irrespective of whether they are fertilised or not. All embryos arrest during embryonic development, many during syncitial development. Defects in cellularisation and/or tissue differentiation are also seen.

P-element has a dominant effect on the timing of eclosion, early eclosion phenotype while entrained to a temperature cycle. Lethality occurs during stage 12 of embryogenesis, the developing nervous system is severely disorganised.