sec8Δ1 mutants hatch at the normal time and initially appear normal in size and behaviour. However, these mutants fail to undergo their first molt and die as first instar larvae. NMJ morphology appears normal in L1 sec8Δ1 mutants. The frequency of spontaneous synaptic currents from these NMJs is normal but the amplitude is mildly but significantly reduced compared to wild type. Glutamate-gated current amplitude is also reduced in these mutants. The amplitude of delayed synaptic receptor closings is not significantly different in the mutants to wild type, indicating that the decrease in glutamate-gated current is due to a loss of functional postsynaptic receptors, rather than a change in receptor properties. The cluster size of both A- and B-type glutamate receptors is significantly reduced in sec8Δ1 first instar larvae. Synaptic microtubule density is significantly increased in sec8Δ1 larvae.