Pdp1^P205 mutants show normal development during embryogenesis and morphologically-normal, motile larvae hatch. However, Pdp1^P205 larvae show a delayed development phenotype. Pdp1^P205 larvae show reduced growth but can survive for long periods as first, second or third instar larvae, with each instar lasting for far longer than in wild type (from many days to over a week). Pdp1^P205 larvae often survive for longer than 3 weeks and some live for 30 days. The ecdysis of Pdp1^P205 larvae is delayed; Pdp1^P205 larvae do not develop second instar mouth hooks until 96 hours AEL compared to 48 hours AEL for wild-type larvae. The addition of exogenous ecdysone does not rescue this phenotype.

Pdp1^P205 mutants are sensitive to their nutritional environment. Larvae raised on grape juice plates supplemented with yeast alone fail to pupate but a small number of Pdp1^P205 larvae are able to pupate and begin to eclose if raised on media supplemented with 25% sucrose in addition to yeast. However, such Pdp1^P205 adults need to be dissected from their pupal cases and die soon afterwards. Protein supplementation does not allow any Pdp1^P205 larvae to pupate.

Pdp1^P205 larvae respond to food normally and the gut and malpighian tubules appear to function normally. However, endoreplication of cells in the gut occurs at a much slower rate than in wild-type guts and the rate is proportionally slower with increasing age of the larvae. A decreased rate of endoreplication is also seen in the fat body and salivary glands of Pdp1^P205 larvae. The rate of mitosis is severely compromised in Pdp1^P205 larvae; the groups of mitotic cells that make up mitotic islands, also known as imaginal nests, in wild-type third instar larvae are virtually absent in Pdp1^P205 larvae and mitotic activity is lower in the brain than in wild-type larvae. Therefore, Pdp1^P205 larvae are growth arrested because of defects in mitosis and endoreplication, rather than because of total starvation.

The effect of the Pdp1^P205 allele is non-autonomous as mutant clones survive and proliferate in all third larval imaginal tissues. These clones are the same size as wild-type clones and replicate at similar levels to wild-type clones.

Mutant homozygotes are developmentally delayed, and are often normal size third instar larvae 14-21 days after egg laying, in contrast to heterozygotes which are adults by this time. Some homozygotes pupate, but only a very small proportion eclose, and these adults die within a day. heterozygous adults are rhythmic for locomotor activity, though they show an average period lengthening of about half an hour.