Delta endotoxins (δ-endotoxins) are a family of pore-forming toxins produced by Bacillus thuringiensis species of bacteria.

During spore formation the bacteria produce crystals of such proteins (hence the name Cry toxins) that are also known as parasporal bodies, next to the endospores; as a result some members are known as a parasporin.

Once activated, the endotoxin binds to the gut epithelium and causes cell lysis by the formation of cation-selective channels, which leads to death.

[7] There continues to be confirmation that AP-Ns do not by themselves affect resistance in some cases, possibly due to sequential binding by the toxin being required to produce its effect.

In this sequence each binding step is theoretically not indispensable, but if it occurs does contribute to the final pore formation result.

Plants with two kinds of delta endotoxins tend to make resistance happen slower, as the insects have to evolve to overcome both toxins at once.