Homozygous lethality occurs mainly during the second larval instar stage (91%), with 6% of homozygotes dying at the second to third instar larval moult and 3% surviving to the third larval instar stage. Animals that die at the second larval instar stage have a distinct morphology; they have two pairs of mouth hooks, one pair with a morphology similar to those of second instar larvae and a second pair with a morphology similar to those of third instar larvae. They also have compound anterior spiracles that are a combination of those from second and third instar larvae. Feeding of second instar homozygous larvae with 20-hydroxyecdysone provides substantial rescue of the developmental defects.